Timed Inhibition of the Renin-Angiotensin System Suppresses the Rise in Blood Pressure Upon Awakening in Spontaneously

AJH 1999;12:1109–1118

Hypertensive Rats Downloaded from https://academic.oup.com/ajh/article/12/11/1109/242530 by guest on 27 September 2021 Jan Oosting, Harrie A. Struijker-Boudier, and Ben J. Janssen

In this study we investigated whether timed antihypertensive response were markedly administration of drugs that inhibit the renin- different. The increase in blood pressure at angiotensin system can be used to blunt the rise in awakening could be blunted much more blood pressure that occurs during the transition effectively by the LD than DL treatment regimen. from the resting to the active period of the day. For Furthermore, as indicated by the trough:peak this purpose we compared in spontaneously ratios, blood pressure profiles were flatter with the hypertensive rats (SHR) the antihypertensive LD than with the DL regimen. Thus, in SHR, 24-h efficacy of the angiotensin converting enzyme rhythms of blood pressure can be modulated by (ACE) inhibitors captopril (doses: 3, 10, and 30 mg/ timed administration of ACE inhibitors and kg/6 h) and enalaprilat (0.3 mg/kg/6 h), and the losartan, such that the early morning rise in blood AT1-receptor antagonist losartan (10 mg/kg/6 h) at pressure is suppressed. Am J Hypertens 1999; two different treatment regimens. The 12:1109–1118 © 1999 American Journal of antihypertensive drugs were given as a continuous Hypertension, Ltd. 6-h infusion either during the transition from the dark to light period (DL) or that from the light to dark period (LD) for 5 consecutive days. For all KEY WORDS: ACE inhibitors, AT1-receptor agents, the average 24-h reduction of blood antagonists, captopril, chronopharmacology, pressure was comparable for the LD or DL circadian rhythms, enalaprilat, losartan, treatment regimen. However, the dynamics of the pharmacodynamics.

orbid events related to hypertension, question as to whether protection against such events such as myocardial infarction, angina can be enhanced by targeting the antihypertensive pectoris, and nonembolic strokes, occur therapy toward this early morning period, which is more often in the early morning hours characterized by a sharp rise in blood pressure and thanM at other times of the day.1,2 This has raised the heart rate.3,4 Recently, one special delivery system has been designed to control the onset and to extend the release of the calcium antagonist verapamil to achieve maximal concentrations during the early morning Received August 10, 1998. Accepted March 22, 1999. 5 From the Department of Pharmacology, Cardiovascular Research surge in blood pressure. For angiotensin converting Institute Maastricht (CARIM), Universiteit Maastricht, Maastricht, enzyme (ACE) inhibitors or AT1-receptor antagonists, The Netherlands. such special formulations do not exist. Obviously, this This work was supported by a research grant of the Dutch Heart Foundation (NHS 90.258) and the ALZA Corporation, Palo Alto, may be explained by the fact that most of these re- California. cently developed drugs have a long pharmacological Address correspondence and reprint requests to Dr. Ben J.A. half life and are applicable as a once-a-day preparation Janssen, Department of Pharmacology, CARIM, Universiteit Maas- tricht, PO Box 616, Maastricht 6200 MD, The Netherlands; e-mail: aimed at controlling blood pressure over the whole [email protected]. 24-h period.

The aim of this study was to test to which extent the Data Acquisition After surgery, Ն3 days of recovery early morning increase in blood pressure can be mod- were allowed to restore 24-h rhythmicity of hemody- ulated by timed administration of drugs that inhibit namics.7 The measurements were done in the home the renin-angiotensin system (RAS). For this purpose cage of the animal. The arterial pressure signal was we compared, in spontaneously hypertensive rats sampled continuously at 512 Hz. Beat-to-beat values (SHR), the antihypertensive efficacy of captopril, ena- of mean arterial pressure (MAP) and heart rate (HR) laprilat, and losartan when given during the transition were calculated on-line. For each rat, data were aver- from the dark to light (DL) period or that from the aged per minute. Mean half hour values were stored light to dark (LD) period. All drugs were given as a on disk for analysis. slow 6-h intravenous infusion starting 3 h before the Protocols Each experiment lasted 1 full week, during transition from LD or DL for 5 consecutive days. The which hemodynamics were continuously measured. Downloaded from https://academic.oup.com/ajh/article/12/11/1109/242530 by guest on 27 September 2021 slow intravenous infusion was given to minimize One group of SHR was treated on 5 consecutive days acute counter-regulatory effects associated with bolus during the transition from the light to the dark period injections, as well as to obtain comparable bioavail- (LD regimen). The other group of SHR received the ability at both periods of the day. Captopril was used infusions during the transition from the dark to the as a reference drug. Enalaprilat was chosen to test light period (DL regimen). In previous studies in whether central nervous effects of ACE inhibition SHR,7,8 we found that the early morning rise in blood could be involved. Enalaprilat does not cross the pressure started approximately 3 h before the begin- 6 blood brain barrier as readily as captopril. Losartan ning of the dark period. To blunt this rise, the drug was chosen to discriminate between effects of ACE infusions were started 3 h (at 3 pm) before the lights inhibition and AT1-receptor blockade. went off (at 6 pm) and were maintained for 6 h. During METHODS the DL regimen, the infusion period was phase-shifted by 12 h. After a 5-day treatment period, hemodynamic Animals Male adult SHR rats (age 14 to 16 weeks) measurements were continued for 2 days to record the weighing 280 to 300 g were used. The rats were ob- effects of withdrawal of the agent. In each animal, a tained from the breeding colonies of the central Ani- time control experiment was performed consisting of a mal Facilities of the Universiteit Maastricht. Experi- 5-day repeated infusion of 0.9 % NaCl at a rate of 2.4 ments were performed according to the institutional mL/6 h. The volume of the infused fluid (2.4 mL/day) guidelines, and were approved by the institutional is not likely to influence hemodynamics, given the fact animal ethics committee. After surgery, the animals that adult rats drink approximately 30 mL of water were housed individually in cages, and were allowed daily. The order of such a 7-day experiment with an normal rat chow and drinking water ad libitum. The antihypertensive agent or with saline was randomized animals were kept in a climatized room with constant in each rat. Using these protocols, the time-dependent temperature (22°C) and humidity (70%) on a 12 h effects of the following agents were compared: capto- light/12 h dark rhythm with lights on at 6 am. From pril at doses of 3, 10, and 30 mg/kg/6 h, enalaprilat at birth on, rats were accustomed to human activity dur- a dose of 0.3 mg/kg/6 h, and losartan at a dose of 10 mg/kg/6 h. If possible, multiple experiments were ing the lights-on period by playing radio music during conducted in one rat. We did not examine plasma this time. hormone levels or drug concentrations concomitantly Surgery All rats were instrumented with an arterial with the hemodynamic measurements. The quantity catheter for measuring blood pressure and a venous of blood needed for such assays did not allow re- catheter for administration of drugs as described in peated blood sampling without interfering with the detail previously.7,8 The catheters were extended to blood pressure measurements. the outside of the cage. The arterial catheter was con- Data Analysis Recordings were made for 7 full days. nected via a hydraulic swivel (model 375/20, Instech For each day of treatment averages of MAP and HR Labs, Plymouth Meeting, PA) to a low-volume dis- were calculated every 30 min. The following measures placement pressure transducer (Microswitch, model were calculated to quantify the drug effects. The effi- 156PC 156WL, Honeywell, Inc, Amsterdam, the Neth- cacy of the drug was determined as the absolute dif- erlands) and kept patent by a continuous infusion of ference of MAP and HR in each 30-min period, with heparinized saline solution (30 U/mL) at a rate of 2.4 the values obtained during the saline infusion in the mL/day. The venous catheter was filled with heparin- same rat. Hence, the average 24-h effect was calculated ized saline (5 U/mL) and plugged. This setup allowed as the mean of 48 of such 30-min values. The early us to measure blood pressure continuously and to morning change in MAP and HR was defined as the administer drugs without disturbing the rats, for pe- absolute differences obtained between the first three riods generally lasting 5 weeks. 30-min periods in the dark period (T1800–1930) and the AJH–NOVEMBER 1999–VOL. 12, NO. 11, PART 1 CHRONOPHARMACOLOGY OF RAS INHIBITORS 1111

TABLE 1. BASELINE HEMODYNAMIC VALUES

DL Regimen LD Regimen

Dose MAP HR MAP HR (mg/kg/6 h) n (mm Hg) (min؊1) n (mm Hg) (min؊1)

Captopril 3 9 149 Ϯ 4 314 Ϯ 9 8 149 Ϯ 1 338 Ϯ 7 Captopril 10 8 150 Ϯ 2 312 Ϯ 7 10 151 Ϯ 4 318 Ϯ 7 Captopril 30 9 151 Ϯ 4 313 Ϯ 8 8 145 Ϯ 3 318 Ϯ 7 Enalaprilat 0.3 8 142 Ϯ 5 341 Ϯ 7 8 144 Ϯ 3 319 Ϯ 7* Losartan 10 8 141 Ϯ 4 344 Ϯ 5 8 141 Ϯ 3 317 Ϯ 6*

Values are 24-h averages over the ﬁrst control day. Values are expressed as means Ϯ SEM. MAP, mean arterial pressure; HR, heart rate; RPP, rate Downloaded from https://academic.oup.com/ajh/article/12/11/1109/242530 by guest on 27 September 2021 pressure product. * P Ͻ .05 DL versus LD regimen. three 30-min periods before the LD infusion was pertensive response, the trough:peak ratio was calcu- started (T1330–1500). These times were based on tracings lated as the quotient of the average MAP value in the obtained in control conditions in which maximal val- 1 h before the infusion (trough) and the maximal ues at awakening were found around 7 pm. To obtain reduction in MAP in the 24-h period after the start of measures of the 24-h dynamic efﬁcacy of the antihy- the infusion (peak). As will be shown, the day-to-day

FIGURE 1. Patterns of mean arterial pressure (MAP) and heart rate (HR) during the 5 days of treatment (D1 to D5) with captopril 10 mg/kg/6 h either at the transition from dark to light period (DL regimen, left panel) or at the transition from the light to dark period (LD regimen, right panel. The effects upon withdrawal of captopril are also shown (R1 and R2). Values are group averages obtained during the infusions of saline (thin line) and during captopril (thick line). The number of animals in each group is given in Table 1. For reasons of clarity, the standard error of the mean (SEM) is not shown. The closed bars denote the lights-off period of the day. The 6-h infusions were given during the periods denoted by the open bars. 1112 OOSTING ET AL AJH–NOVEMBER 1999–VOL. 12, NO. 11, PART 1 Downloaded from https://academic.oup.com/ajh/article/12/11/1109/242530 by guest on 27 September 2021

FIGURE 2. Patterns of mean arterial pressure (MAP) and heart rate (HR) during the 5 days of treatment (D1 to D5) with losartan 10 mg/kg/6 h either at the transition from dark to light period (DL regimen, left panel) or at the transition from the light to dark period (LD regimen, right panel). The effects upon withdrawal of losartan are also shown (R1 and R2). Values are group averages obtained during the infusions of saline (thin line) and during losartan (thick line). The number of animals in each group is given in Table 1. For reasons of clarity the SEM is not shown. The closed bars denote the lights-off period of the day. The 6-h infusions were given during the periods denoted by the open bars.

variability of this measure was high. For this reason included in the analysis becase of the run-in effects of we calculated, as another estimate of how flat the 24-h the drugs. Only average values found at days 3, 4, and blood pressure profile was, the average MAP differ- 5 of treatment were included in the evaluation. Differ- ence between the 12-h light and 12-h dark period. ences between drugs were tested by ANOVA fol- lowed by a post hoc Scheffe´’s t test. Statistical signi- Drugs Captopril was purchased from Sigma Chem- ficance was accepted at P Ͻ .05. icals (Axel, The Netherlands). Enalaprilat and losartan were kindly donated by Merck Sharp and Dohme RESULTS (Haarlem, The Netherlands). All agents were dis- solved in saline and frozen in small aliquots before Baseline Hemodynamics Baseline hemodynamic use. values of MAP and HR are compared between groups of rats in Table 1. The baseline values were defined as Statistics Statistical evaluation was performed by the average 24-h values of MAP and HR during day 1 analysis of variance (ANOVA). Hemodynamic effects of intravenous saline infusion. Table 1 shows that occurring over time during the saline or drug infusion baseline values of MAP were not different between in each rat were defined as a within-factor effect. the groups of rats that received saline during the DL Differences between the effects caused by the LD and or the LD treatment regimen. Slight but significant DL treatment regimen, as well as differences between differences were found for HR between the groups agents, were compared as between-factor effects. Data treated with enalaprilat and losartan. This is most obtained during the first 2 days of treatment were not likely due to biological variation between the different AJH–NOVEMBER 1999–VOL. 12, NO. 11, PART 1 CHRONOPHARMACOLOGY OF RAS INHIBITORS 1113

TABLE 2. COMPARISON OF THE AVERAGE 24-h HEMODYNAMIC EFFECTS OBTAINED DURING THE TWO DIFFERENT TREATMENT REGIMENS

DL Regimen LD Regimen

Average 24-h Dose MAP HR MAP HR (Difference (mg/kg/6 h) n (mm Hg) (min؊1) n (mm Hg) (min؊1

Captopril 3 9 Ϫ8 Ϯ 411Ϯ 78Ϫ10 Ϯ 11Ϯ 5 Captopril 10 8 Ϫ15 Ϯ 324Ϯ 610Ϫ13 Ϯ 2 Ϫ1 Ϯ 9 Captopril 30 9 Ϫ15 Ϯ 214Ϯ 38Ϫ19 Ϯ 29Ϯ 5 Enalaprilat 0.3 8 Ϫ6 Ϯ 5 Ϫ5 Ϯ 12 8 Ϫ12 Ϯ 21Ϯ 5 Losartan 10 8 Ϫ13 Ϯ 411Ϯ 88Ϫ17 Ϯ 39Ϯ 5 Downloaded from https://academic.oup.com/ajh/article/12/11/1109/242530 by guest on 27 September 2021 Values are the average difference (over days 3–5) between values obtained during saline control and the indicated treatment. Values are expressed as means Ϯ SEM. * P Ͻ .05 LD versus DL treatment regimen. animals in each group. However, it does not hamper In all groups, the 5-day repeated infusion of 2.4 mL the analysis because paired observations (saline ver- saline solution in 6 h did not alter the 24-h pattern of sus drug effects) were obtained in each rat. blood and heart rate. As shown in Figure 1 and Figure 2, the 24-h proﬁles of MAP and HR remained unal- tered for the 7-day control period when saline was infused either during the LD or DL regimen. Stability of the hemodynamics during the week of saline infusions was assessed in all groups by ANOVA with time as a within-factor effect. The analysis revealed that in none of the groups MAP and HR were signiﬁcantly different between the days of the week.

Time-Related Effects of Treatment With Captopril The time-related effects during the 5-day treatment with captopril 10 mg/kg/6 h are summarized in Fig- ure 1. In both experiments the antihypertensive properties of captopril showed increasing efficacy over the ensuing days of treatment with only a small reduction in blood pressure occurring during the first infusion, and Ͼ30 mm Hg during the infusion of captopril at day 5. This effect was more pronounced when captopril was given during the LD than during the DL regimen. In the latter case, the full antihypertensive effect was obtained at day 3 of infusion. The average 24-h changes in MAP and HR were not different for the LD and DL regimen with the three doses of captopril (Table 2). However, the dynamics of the response to captopril was dependent on the time of administration. As shown in the Figure 1 and Figure 3, the LD regimen of captopril blunted the rise of blood pressure during the transition from the light to dark period. With the DL regimen, the initial decrease of FIGURE 3. Effects of treatment with captopril (10 mg/kg) on MAP during the first 3 h of infusion was low. How- mean arterial pressure (MAP) and heart rate (HR) over a full 24-h ever, at the onset of the sleeping period, MAP fell period. Infusions were given either at the transition from the light to markedly. The values for the early morning rise of dark period (LD regimen, open circles) or at the transition from the dark to light period (DL regimen, closed circles). Values are means MAP and HR are compared in detail in Table 3. As over days 3 to 5 of treatment. The values obtained during the saline shown in this table, the LD regimen of captopril re- infusions were averaged over the morning and evening groups duced MAP at awaking significantly more than in the (straight lines).The number of animals in each group is given in Table DL regimen. During the LD regimen HR was slightly 1. The closed bars denote the lights-off period of the day. (20 to 30 beats/min) increased. Statistical significance 1114 OOSTING ET AL AJH–NOVEMBER 1999–VOL. 12, NO. 11, PART 1

TABLE 3. EFFECTS OF TIMED TREATMENT ON EARLY MORNING HEMODYNAMIC CHANGES

DL Regimen LD Regimen

Average 24-h Dose MAP HR MAP HR Difference (mg/kg/6 h) n (mm Hg) (beats/min) n (mm Hg) (beats/min)

Saline 29 6.3 Ϯ 0.7 51 Ϯ 3 27 3.9 Ϯ 0.7 48 Ϯ 3 Captopril 3 3 9 8.1 Ϯ 2.1 40 Ϯ 10 8 Ϫ6.9 Ϯ 2.2* 71 Ϯ 3 Captopril 10 10 8 9.2 Ϯ 1.3 49 Ϯ 510Ϫ7.6 Ϯ 2.1* 74 Ϯ 4* Captopril 30 30 9 7.7 Ϯ 0.7 47 Ϯ 78Ϫ19.6 Ϯ 1.8* 79 Ϯ 5 Enalaprilat 0.3 8 7.8 Ϯ 1.6 49 Ϯ 58Ϫ8.2 Ϯ 1.8* 70 Ϯ 4 Losartan 10 8 7.6 Ϯ 0.9 43 Ϯ 2 8 0.4 Ϯ 3.5 40 Ϯ 9 Downloaded from https://academic.oup.com/ajh/article/12/11/1109/242530 by guest on 27 September 2021 The early morning changes were deﬁned as the absolute changes of mean arterial pressure (MAP) and heart rate (HR) before the rise in pressure at

T1330–1500 and at the peak increase found in control rats between T1800–1930. Values are the average difference (over days 3 to 5) between values obtained during saline control and the indicated treatment. Values are expressed as means Ϯ SEM. * P Ͻ .05 LD versus DL regimen. was only obtained for the 10 mg/kg dose. After ces- 6. Then, when the lights went on MAP fell again below sation of the last infusions of captopril, MAP returned control on day 6, although no drug was infused (see to near control values during the dark period on day Figure 1). This effect was absent on day 7, the second day of withdrawal. Time-Related Effects of Enalaprilat After treatment with enalaprilat, there was a progressive lowering of MAP over the days, reaching stability after 3 days of infusion (data not shown). The 24-h profiles obtained with this agent were very comparable to those ac- quired with captopril (Figure 4, Tables 4, 5). As indicated in Table 3, also, enalaprilat blunted more effectively the early morning blood pressure rise after the LD than after the DL regimen. The average 24-h reduction of MAP was approximately 6 mm Hg greater with the LD regimen than with the DL regimen. How- ever this effect did not reach statistical significance (Table 2). Time-Related Effects of Losartan The antihypertensive response to repeated infusions of this agent be- came stable at day 3 of the repeated infusions (Figure 2). During both treatment regimens, the average daily reduction in MAP was approximately 15 mm Hg (Ta- ble 2). However, despite the long term efficacy of this agent, during the DL regimen the blood pressure fell at the onset of the lights-on period and increased until the next infusion. In contrast, during the LD regimen the 24-h blood pressure patterns remained relatively flat (Figure 2 and Figure 5) and trough values of MAP remained low. Accordingly, the early morning rise was blunted, but to a lesser extent as found with the short-acting agents captopril and enalaprilat. Further- FIGURE 4. Effects of treatment with enalaprilat (0.3 mg/kg) on more, as a result of the long term efficacy of the LD mean arterial pressure (MAP) and heart rate (HR) over a full 24-h regimen, trough:peak ratios were greater and dark/ period. Infusions were given either at the transition from the light to light differences of MAP were smaller than during the dark period (LD regimen, open circles) or at the transition from the dark to light period (DL regimen, closed circles). Values are means DL regimen (Tables 4, 5). over days 3 to 5 of treatment. The values obtained during the saline DISCUSSION infusions were averaged over the morning and evening groups (straight lines).The number of animals in each group is given in Table The main finding of this study is that, with timed 1. The closed bars denote the lights-off period of the day. administration of RAS inhibitors, the blood pressure AJH–NOVEMBER 1999–VOL. 12, NO. 11, PART 1 CHRONOPHARMACOLOGY OF RAS INHIBITORS 1115

TABLE 4. DYNAMIC MEASURES OF ANTIHYPERTENSIVE EFFICACY: AVERAGE VALUES AND BETWEEN DAY VARIABILITY OF TROUGH:PEAK RATIOS DL Regimen LD Regimen Dose (mg/kg/6 h) n T/P (%) CV (%) n T/P (%) CV (%)

Captopril 3 9 27 Ϯ 13 131 Ϯ 62 8 29 Ϯ 11 87 Ϯ 17 Captopril 10 8 18 Ϯ 7 126 Ϯ 47 10 48 Ϯ 5* 76 Ϯ 21 Captopril 30 9 30 Ϯ 3 110 Ϯ 37 8 34 Ϯ 785Ϯ 26 Enalaprilat 0.3 8 20 Ϯ 13 89 Ϯ 19 8 24 Ϯ 11 264 Ϯ 97 Losartan 10 8 27 Ϯ 7 142 Ϯ 77 8 53 Ϯ 8* 62 Ϯ 18

The trough:peak ratio was calculated as the quotient of the average MAP value in the hour preceding the infusion (trough) and the maximal reduction Downloaded from https://academic.oup.com/ajh/article/12/11/1109/242530 by guest on 27 September 2021 in MAP in the 24-h period after the start of the infusion (peak). Values are averages calculated over days 3 to 5 of treatment. The coefﬁcient of variation indicates the average between day variability of this measure. Values are expressed as means Ϯ SEM. * P Ͻ .05 LD versus DL regimen.

rhythm of SHR can be modulated selectively to blunt pressure averaged approximately 8 mm Hg and was the early morning rise in blood pressure. Although the not different from values obtained during saline. This average reductions of blood pressure were compara- indicates that high plasma concentrations of these ble in these nocturnally active animals, the rise of agents are necessary at the transition from sleep to blood pressure at awakening was more effectively activity to suppress this rise in blood pressure. This reduced by administering the antihypertensive agents applies especially to the short acting agents but also 3 h before the onset of the dark period (LD regimen) for the long acting agent losartan. than 3 h before onset of the lights-on period (DL When RAS inhibitors were infused 3 h before the regimen). Additionally, the indices of the 24-h dy- lights-on period, the pressure fall was initially minor; namic variability of blood pressure were lower during however, as soon as the lights went on, blood pressure the LD than during the DL regimen. On withdrawal of dropped considerably. Because of this secondary fall the agents, blood pressure returned gradually to con- in pressure 24-h blood pressure profiles were, as indi- trol. Rebound hypertension was never observed. cated by the trough:peak ratios and 12 h day/12 h Why cardiovascular events cluster preferentially in night differences in MAP, more variable during the the early morning hours is not exactly known. A va- 1 DL than during the LD regimen. This aspect may be of riety of mechanisms have been implicated. In the clinical relevance, because target organ damage is re- present discussion we focus only on hemodynamic lated not only to the absolute level of blood pressure mechanisms. In humans9 as well as in SHR,10 resis- but also to its hour-to-hour variability.13,14 However, tance to blood flow is highest at the end of the sleeping the data on the trough:peak ratios obtained in this period. When activity is resumed, cardiac output in- study in SHR must be interpreted with caution, be- creases and peripheral resistance falls.10 During the cause the day-to-day variability of this index was high transition from activity to sleep, these hemodynamic and hardly reached clinically recommended val- changes are reversed. Based on these observations, we 15,16 hypothesize that, in case peripheral resistance fails to ues. decrease at awakening, the heart is opposed with an Increased responsiveness of blood pressure to RAS inhibition in the lights-on period has been noticed elevated afterload, which increases the risk for cardio- 8,17,18 vascular events. For this reason it may be beneficial to before. However, in these studies in SHR and in lower peripheral resistance before waking. This study renin-overexpressing transgenic (TGR[mRen-2]27) shows that this strategy is feasible in SHR by timed rats, single bolus injections were applied. The present administration of RAS inhibitors. The antihyperten- study design shows that run-in effects contribute sig- sive effect of these agents is, to a major extent, due to nificantly to the antihypertensive efficacy of RAS in- their vasodilating properties.11,12 As shown in Figures hibitors. The increasing efficacy over the course of 3, 4, and 5, blood pressure falls during the first3hof days may be explained by standard pharmacokinetic infusion during the LD treatment regimen. Then, mechanisms such as increasing tissue penetration and when the lights go off, there is a small rise in blood accumulation of these drug or their metabolites.19,20 pressure but the antihypertensive effect is maintained However, the fact that these run-in effects occurred in and the early morning rise of blood pressure is effec- a similar fashion with captopril as well with losartan tively blunted. In contrast, during the DL regimen of suggests that, irrespective of the variable pharmacoki- the RAS inhibitors, the early morning rise of blood netics, a common pharmacodynamic mechanism is 1116 OOSTING ET AL AJH–NOVEMBER 1999–VOL. 12, NO. 11, PART 1

system to these drugs. ACE inhibitors and losartan have natriuretic properties, and the loss of salt may have increased the extent to which blood pressure becomes dependent upon renin or angiotensin II (AII). This dependency is likely to be highest at the end of each dose interval and, consequently, the next dose of the antihypertensive agents leads to a greater fall in blood pressure. These observations support the view that the physiological production of renin and, hence, availability of AII determine the 24-h variation in the antihypertensive efficacy of the ACE inhibitors and losartan. The time varying activity of plasma and tis- Downloaded from https://academic.oup.com/ajh/article/12/11/1109/242530 by guest on 27 September 2021 sue ACE activity seems only of minor importance in both SHR21 and in humans.22,23 In rats,24,25 as well as in humans,26,27 plasma AII concentrations and renin activity are higher during the resting than during the active period. The fact that the diurnal variation of renal blood flow shows a trough value during this period28 corroborates the finding that kidney-derived renin is the rate-limiting factor in the production of AII.29 The physiological variation in the degree to which blood pressure depends on renin production may also explain why, upon withdrawal of the last LD infusion of captopril and losartan, a secondary fall in pressure was observed at day 6 during the progression of the resting period, while no drug was infused (Figures 1 and 2). Comparable observa- FIGURE 5. Effects of treatment with losartan (10 mg/kg) on tions have also been made in patients upon with- mean arterial pressure (MAP) and heart rate (HR) over a full 24-h drawal of an ACE inhibitor.30 period. Infusions were given either at the transition from the light to Time-dependent antihypertensive efficacy was ob- dark period (LD regimen, open circles) or at the transition from the served with the AT -receptor antagonist and the ACE dark to light period (DL regimen, closed circles). Values are means 1 over days 3 to 5 of treatment. The values obtained during the saline inhibitors. This indicates that the time varying effect of infusions were averaged over the morning and evening groups kinins on the vascular system are of minor importance. (straight lines).The number of animals in each group is given in Table This latter aspect is supported by a recent study in 1. The closed bars denote the lights-off period of the day. TGR in which time-dependent blood pressure reductions after enalaprilat and losartan were comparable.18 A specific effect of brain AII may be ruled out, too, involved. From the blood pressure patterns, one may because the effects of captopril were not different from deduce that the repeated infusion of the ACE inhibi- those of enalaprilat, an agent that does not readily tors and losartan has sensitized the cardiovascular cross the blood–brain barrier.6

TABLE 5. DYNAMIC MEASURES OF ANTIHYPERTENSIVE EFFICACY: AVERAGE DIFFERENCE BETWEEN 12-h DARK AND 12-h LIGHT PERIOD

DL Regimen LD Regimen

⌬MAP Dose Saline Treatment Saline Treatment Dark-light (mg/kg/6 h) n (mm Hg) (mm Hg) n (mm Hg) (mm Hg)

Captopril 3 9 3.2 Ϯ 1.3 6.0 Ϯ 0.8† 8 5.0 Ϯ 0.8 3.3 Ϯ 0.7*† Captopril 10 8 4.9 Ϯ 0.7 10.3 Ϯ 1.0† 10 5.3 Ϯ 1.0 2.8 Ϯ 1.1* Captopril 30 9 4.5 Ϯ 0.5 9.9 Ϯ 0.8† 8 1.6 Ϯ 1.0 Ϫ3.1 Ϯ 0.6*† Enalaprilat 0.3 8 5.5 Ϯ 1.2 6.9 Ϯ 0.9 8 1.5 Ϯ 1.0 Ϫ0.5 Ϯ 1.5 Losartan 10 8 4.2 Ϯ 1.4 8.9 Ϯ 0.9† 8 3.1 Ϯ 1.1 1.6 Ϯ 1.5*†

Values are averages calculated over days 3 to 5 of treatment. Values are expressed as means Ϯ SEM. * P Ͻ .05 LD versus DL regime. †PϽ .05 treatment versus saline control. AJH–NOVEMBER 1999–VOL. 12, NO. 11, PART 1 CHRONOPHARMACOLOGY OF RAS INHIBITORS 1117

Therapeutic Implications In the current study, we 11. Smits JFM, Struyker-Boudier HAJ: Systemic and re- have shown that blood pressure patterns in hyperten- gional hemodynamics following acute inhibition of an- sive animals can be modulated with timed dosing of giotensin I converting enzyme in the conscious spontaneously hypertensive rat. Prog Pharmacol 1984;5:39– drugs that antagonize the renin-angiotensin system. 49. To our knowledge, four studies in patients have com- 12. Widdop RE, Gardiner SM, Kemp PA, Bennet T: Com- pared the efficacy of a morning versus evening regi- parison of the regional haemodynamic effects of the 23,31–33 men with ACE inhibitors. In all four studies it AT1-receptor antagonists, losartan and EXP 3174, in was shown that the timing of the administration of water-deprived Brattleboro rats. Br J Pharmacol 1993; drugs was important for the ensuing circadian blood 108:684–688. pressure pattern. However, the studies disagree to a 13. Voogel AJ, Van Der Meulen JHP, Van Montfrans GA: certain extent about the optimal time of administra- Effects of antihypertensive drugs on the circadian tion. Of course, which 24-h blood pressure pattern has blood pressure profile. J Cardiovasc Pharmacol 1996; Downloaded from https://academic.oup.com/ajh/article/12/11/1109/242530 by guest on 27 September 2021 28:463–469. an optimal protection for the morbid events related to hypertension has to be established in clinical trials. 14. Parati G, Pomidossi G, Albini F, Malaspina D, Mancia G: Relationship of 24-hour blood pressure mean and Our data in SHR suggest the development of ACE variability to severity of target-organ damage in hyper- preparations or AT1-receptor antagonists that have a tension. J Hypertens 1987;5:93–98. controlled onset and anticipate the circadian varia- 15. Lipicky RJ: Trough:peak ratio: the rationale behind the tions in components of the renin-angiotensin system. United States Food and Drug Administration recom- mendations. J Hypertens 1994;12(suppl 8):s17–s19. ACKNOWLEDGMENT 16. Meredith PA, Elliott HL: FDA guidelines on trough: We thank Caroline Eerdmans-Tyssen for expert technical peak ratios in the evaluation of antihypertensive assistance. agents. J Cardiovasc Pharmacol 1994;23(suppl 5):S26– REFERENCES S30. 17. Lemmer B, Witte K, Makabe T, Ganten D, Mattes A: 1. Muller JE, Tofler GH, Stone PH: Circadian variation Effects of enalaprilat on circadian profiles in blood and triggers of onset of acute cardiovascular disease. pressure and heart rate of spontaneously and trans- Circulation 1989;4:733–743. genic hypertensive rats. J Cardiovasc Pharmacol 1994; 2. Marler JR, Price TR, Clark GL, Muller JE, Robertson T, 23:311–314. Mohr JP, Hier DB, Wolf PA, Caplan LR, Foulkes MA: 18. Schnecko A, Witte K, Lemmer B: Effects of the angio- Morning increases in onset of ischemic stroke. Stroke tensin II receptor antagonist losartan on 24-hour blood 1989;20:473–476. pressure profiles of primary and secondary hyperten- 3. Gould BA, Raftery EB: Twenty-four-hour blood pres- sive rats. J Cardiovasc Pharmacol 1995;26:214–221. sure control: an intraarterial review. Chronobiol Int 19. Gohlke P, Unger T: Angiotensin-converting enzyme 1991;8:495–505. inhibitors, in Swales JD (ed): Textbook of Hypertension. 4. Materson BJ, Preston RA: Classic therapeutic trials in Blackwell Scientific Publications, Oxford, 1994, pp hypertension. Am J Hypertens 1991;4:449S–453S. 1115–1127. 5. Neutel JM, Alderman M, Anders RJ, Weber MA: Novel 20. Belz GG, Kirch W, Kleinbloesem CH: Angiotensin-con- delivery system for verapamil designed to achieve verting enzyme inhibitors. Relationship between phar- maximal blood pressure control during the early morn- macodynamics and pharmacokinetics. Clin Pharmaco- ing period. Am Heart J 1997;132:1202–1206. kinet 1988;15:295–318. 6. Golhke P, Urbach H, Scho¨lknes BA, Unger T: Inhibition 21. Stepien M, Witte K, Lemmer B: Chronobiologic evalu- of converting enzyme in the cerebrospinal fluid of rats ation of angiotensin-converting enzyme activity in se- after oral treatment with converting enzyme inhibitors. rum and lung tissue from normotensive and spontane- J Pharmacol Exp Ther 1989;249:609–616. ously hypertensive rats. Chronobiol Int 1993;10:331– 7. Janssen BJA, Tyssen CM, Struyker-Boudier HAJ: Mod- 337. ification of circadian blood pressure and heart rate variability by five different antihypertensive agents in 22. Weisser K, Schloos J, Lehmann K, Du¨ sing R, Vetter H, spontaneously hypertensive rats. J Cardiovasc Pharma- Mutschler E: Pharmacokinetics and converting enzyme col 1991;17:494–503. inhibition after morning and evening administration of oral enalapril to healthy subjects. Eur J Clin Pharmacol 8. Janssen BJA, Oosting J, Tyssen CM, Struyker-Boudier 1991;40:95–99. HAJ: Time-dependent efficacy of antihypertensive agents in spontaneously hypertensive rats. Chronobiol 23. Witte K, Weisser K, Neubeck M, Mutschler E, Lehmann Int 1993;10:420–434. K, Hopf R, Lemmer B: Cardiovascular effects, pharmacokinetics, and converting enzyme inhibition of enala- 9. Veerman DP, Imholz BPM, Wieling W, Wesseling KH, pril after morning versus evening administration. Clin Van Montfrans GA: Circadian profile of systemic he- Pharmacol Ther 1993;54:177–186. modynamics. Hypertension 1995;26:55–59. 10. Oosting J, Struijker-Boudier HAJ, Janssen BJA: Circa- 24. Hilfenhaus M: Circadian rhythm of the renin-angioten- dian and ultradian control of cardiac output in sponta- sin-aldosterone system in the rat. Arch Toxicol 1976;36: neous hypertension in rats. Am J Physiol 1997;273: 305–316. H66–H75. 25. DeForrest JM, Davis JO, Freeman RH, Stephgens GA, 1118 OOSTING ET AL AJH–NOVEMBER 1999–VOL. 12, NO. 11, PART 1

Watkins BE: Circadian changes in plasma renin activity 30. Smith DHG, Neutel JM, Black HR, Schoenberger JA, and plasma aldosterone concentration in two-kidney Weber MA: Once-daily monotherapy with trandolapril hypertensive rats. Hypertension 1979;1:142–149. in the treatment of hypertension. J Hum Hypertens 1996;10:129–134. 26. Modlinger RS, Scharif-Zadeh K, Ertel NH, Gutkin M: The circadian rhythm of renin. J Clin Endocrinol Metab 31. Palatini P, Racioppa A, Raule G, Zaninotto M, Penzo M, 1976;43:1276–1282. Pessina AC: Effect of timing of administration on the plasma ACE inhibitory activity and the antihyperten- 27. Kool MJ, Wijnen JA, Derkx FH, Struijker-Boudier HA, sive effect of quinapril. Clin Pharmacol Ther 1992;52: Van-Bortel LM: Diurnal variation in prorenin in rela- 378–383. tion to other humoral factors and hemodynamics. Am J Hypertens 1994;7:723–730. 32. Morgan T, Anderson A, Jones E: The effect on 24 h blood pressure control of an angiotensin converting 28. Delp MD, Manning O, Bruckner JV, Armstrong RB: enzyme inhibitor (perindopril) administered in the

Distribution of cardiac output during diurnal changes morning or at night. J Hypertens 1997;15:205–211. Downloaded from https://academic.oup.com/ajh/article/12/11/1109/242530 by guest on 27 September 2021 of activity in rats. Am J Physiol 1991;261:H1487–H1493. 33. Palatini P, Mos L, Motolese M, Mormino P, Del Torre 29. Danser AH, van Kesteren CA, Bax WA, Derkx FH, M, Varotto L, Pavan E, Pessina AC: Effect of evening Saxena PR, Schalekamp MA: Prorenin, renin, angioten- versus morning benazepril on 24-hour blood pressure: sin-converting enzyme in normal and failing human a comparative study with continuous intraarterial hearts. Evidence for renin binding. Circulation 1997;96: monitoring. Int J Clin Pharmacol Ther Toxicol 1993;6: 220–226. 295–300.