Journal of Human (1998) 12, 511–516  1998 Stockton Press. All rights reserved 0950-9240/98 $12.00 http://www.stockton-press.co.uk/jhh ORIGINAL ARTICLE , but not , improves -dependent in hypertensive patients

J Millga˚rd, A Ha¨gg, M Sarabi and L Lind Department of Internal Medicine, University Hospital of Uppsala, Sweden

The present study aimed to investigate the influence of decline in pressure (BP) 1 h after administration -the -converting enzyme (ACE)-inhibitor cap- (؊11 to 10 mm Hg/؊8 to 7 mm Hg), captopril signifi topril and the Ca-antagonist nifedipine on endothelium- cantly potentiated the vasodilator response to MCh dependent vasodilation (EDV) in the forearm of hyper- (؉32 ؎ 13%, MCh 4 ␮g/min, P Ͻ 0.01) but not SNP, while tensive patients. Twenty-three middle-aged untreated nifedipine did not significantly alter the response to hypertensive patients underwent evaluation of EDV and either MCh or SNP. The improvement in vasodilator endothelium-independent vasodilation (EIDV) in the response to MCh induced by captopril was closely .(P Ͻ 0.01 ,0.72 ؍ forearm, by means of local intra-arterial infusions of related to the reduction in BP (r methacholine (MCh, evaluating EDV) and sodium- Third, in the pilot study, 3 months of captopril treat- nitroprusside (SNP, evaluating EIDV), before and 1 h ment induced a significant potentiation of the vaso- ,after intake of either captopril (25 mg) or nifedipine dilator response to MCh (؉34 ؎ 17%, MCh 4 ␮g/min (10 mg) in a randomised, double-blind fashion. A P Ͻ 0.05) in parallel with a significant BP reduction matched normotensive control group was investigated (؊22 ؎ 24/13 ؎ 13 mm Hg, P Ͻ 0.05), while the response at baseline conditions only. Five of the hypertensives to SNP was unchanged. were also evaluated after 3 months of treatment with In conclusion, the present study confirmed that captopril 25 mg twice daily in an open pilot study. is associated with a defect in First, the vasodilation induced by methacholine EDV. Furthermore, an improvement in EDV was seen in (MCh), but not SNP, was significantly attenuated in the hypertensive patients shortly after administration of hypertensive patients compared to the normotensive captopril, but not nifedipine. In addition, a significant controls (P Ͻ 0.001 at MCh 4 ␮g/min). beneficial effect on EDV was seen in a small pilot study Second, although the two induced a similar during long-term treatment with captopril.

Keywords: hypertension; ; endothelium; vasodilation; ACE-inhibitors; -antagonists

Introduction tension,10 as well as promote vascular compli- cations,11 improving EDV in this patient group may By elaboration of several vasoactive factors such as be beneficial in several ways. (NO), -1 (ET-1), prosta- Previous investigations of the endothelial effects glandins and yet unidentified endothelium-derived of anti-hypertensive have produced hyperpolarising factor (EDHF), the vascular endo- disappointing results,8 even if there are some indi- thelium plays a crucial role in the regulation of cations of a positive effect of angiotensin-converting blood flow, peripheral resistance and thereby blood 4,12 1 enzyme (ACE)-inhibition. pressure (BP). The present study aimed to investigate if the ACE- Several investigators have found an impaired inhibitor captopril or the Ca-antagonist nifedipine endothelium-dependent vasodilation (EDV) in the could improve EDV in the forearm vascular bed in forearm circulation in patients with primary hyper- untreated hypertensive patients. The acute effects 2–9 tension, a defect that has been proposed to com- induced by a single dose of captopril or nifedipine prise a dysfunctional NO-system or an over-pro- were investigated in a randomised, double-blind duction of an endothelium derived contracting study, while the effects of long-term treatment with factor. Whether this is a pri- captopril was studied in a small, open pilot study. mary or secondary phenomenon of the hypertensive is so far not known. However, as a defect in endothelial function might be of pathogenetic Materials and methods importance in the development of primary hyper- Subjects The study population (Table 1) consisted of 23 Correspondence: Dr Lars Lind, Dept of Internal Medicine, Univer- patients (22 men and one woman) with essential sity Hospital of Uppsala, S-751 85 Uppsala, Sweden hypertension defined as diastolic BP (DBP) Ͼ95 Received 10 October 1997; revised and accepted 8 May 1998 mm Hg without treatment confirmed by BP re- Anti-hypertensive treatment and endothelial function J Millga˚rd et al 512 Table 1 Basic characteristics in the study sample undertaken in one of the arms while the contra- lateral arm served as a control. Evaluations of FBF Normotensive Hypertensive were made by calculations of the mean of five con- controls patients secutive recordings. The reproducibility of this test of EDV and endothelium-independent vasodilation n 25 23 (EIDV) was evaluated in 10 healthy young volun- ± ± Age (years) 54 11 55 11 teers in whom the investigation was performed Body mass index (kg/m2)26± 2.7 27 ± 3.0 before and after 2 h of intravenous saline infusion, Systolic BP (mm Hg) 124 ± 13 162 ± 23*** as well as repeated after 2–3 weeks. Baseline resting Diastolic BP (mm Hg) 81 ± 7.7 100 ± 8.1*** FBF showed a variation less than 10%, while FBF ± ± during vasodilation induced by either MCh or SNP Serum cholesterol (mmol/l) 5.3 0.8 5.5 0.9 showed a variation of less than 5%, in the short- Baseline forearm 19 ± 6.1 22 ± 8.6 term (2 h) as well as the long-term (2–3 weeks) per- (mm Hg/ml/min/100 ml ) spective. Forearm circumference (mm) 294 ± 14 294 ± 18 In the present study, the measurements of EDV and EIDV were undertaken at baseline conditions, ***Denotes P Ͻ 0.001 vs normotensive controls. ± 1 h after intake of either captopril or nifedipine Values are expressed as means standard deviation (s.d.). (n = 21). Evaluations of the vasodilation in normot- ensive subjects were only undertaken at baseline cordings at different locations. The presence of sec- conditions and no oral drugs were given in this ondary hypertension was excluded by laboratory group. BP measurements were made with a mercury tests and physical examination. Another two sub- sphygmomanometer in parallel with the FBF re- jects entered the trial, but were later excluded as sec- cordings. ondary hypertension was discovered. The study protocol was approved by the Hospital Ten of the patients were previously untreated and ethics committee and informed consent was the remaining 13 had been without anti-hyperten- obtained from all participants. sive treatment for at least 3 weeks at the time of the investigation. Anti-hypertensive drugs An age- and sex-matched normotensive (BP below Captopril (25 mg, n = 12) or nifedipine (10 mg, n = 9) 140/90 mm Hg) control population (n = 25, Table 1) was administered orally in a randomised, double- was randomly recruited from the general population blind manner for the evaluation of the acute effects in the city of Uppsala. All controls were without his- of these drugs. tory of cardiovascular disorders and were free from Furthermore, five patients received 25 mg of cap- any medications. topril twice a day for 3–6 months in an open fashion in a pilot study. The follow-up measurements in Measurements of forearm blood flow (FBF) these five patients were performed at least 8 h after intake of the last dose. The patients included in the During the blood flow measurements, the subjects long-term study were similar in demographies and were supine in a quiet room maintained at a con- BP distribution as the hypertensive sample as a stant temperature (21–23°C). An arterial cannula whole. was inserted into the brachial of one arm for regional infusions of MCh (muscarinic agonist) and SNP (nitric oxide donor). Muscarinic agonists have Calculations previously been shown to induce EDV13 while NO Mean artery pressure (MAP) was calculated as one- donors act as direct relaxants, third of the pressure (systolic BP (SBP) minus inducing vasodilation independent of the endo- DBP) added to DBP. thelium. Forearm vascular resistance (FVR) was given by The vasodilative -infusions were given dur- MAP divided by FBF. In the present study vaso- ing 5 min for each dose with a 20 min wash-out per- dilation was evaluated by the reduction in FVR iod between the two drugs. The infused dosages achieved by MCh or SNP-infusion in relation to ␮ ␮ − were 2 and 4 g/min for MCh and 5 and 10 g/min baseline FVR, (FVRdrug FVRbaseline)/FVRbaseline. for SNP. These drugs were given in a random order at a rate of 1 ml/min. Statistical analysis Before and at the end of the different dosages of Treatment effects were evaluated by two-way the two drugs, FBF was measured in both forearms ANOVA in the short-term study and with the Wil- by venous occlusion plethysmography according to coxon signed rank sum test (two-tailed) in the long- the following. A mercury in-silastic strain gauge, term pilot study. Differences between groups were connected to a calibrated plethysmograph, was calculated by means of one-way ANOVA; P Ͻ 0.05 placed on the upper third of the forearm, which was regarded as significant. rested comfortably slightly above the level of the . Venous occlusion was achieved by a BP cuff applied proximal to the elbow and inflated to 40 Results mm Hg by a rapid cuff inflator; approximately four Baseline characteristics for the hypertensive sub- inflations per minute, each of about 7 sec duration jects and the normotensive controls are given in were performed. The vasodilative infusions were Table 1. Anti-hypertensive treatment and endothelial function J Millga˚rd et al 513 The hypertensive patients presented a signifi- Table 2 The hypertensive treatment groups, baseline character- cantly attenuated vasodilation induced by MCh- istics infusion compared to the normotensive control sub- Ͻ Patients Patients jects (P 0.001 for both doses), while the response receiving receiving to SNP was not significantly different between captopril nifedipine patients and controls (Figure 1). n 12 9 Captopril, short-term effects Age (years) 52 ± 10 57 ± 10 2 ± ± The baseline characteristics, as well as the vaso- Body mass index (kg/m )272.4 26 3.2 dilation induced by MCh- or SNP-infusion, were Systolic BP (mm Hg) 159 ± 16 164 ± 26 comparable in the two groups before the drugs were Diastolic BP (mm Hg) 101 ± 8.2 101 ± 9.5 given (Table 2). Serum cholesterol (mmol/l) 5.6 ± 1.1 5.3 ± 0.8 A significant reduction in MAP was observed in Baseline forearm vascular 22 ± 7.8 21 ± 10 the hypertensive patients 1 h after administration of resistance either captopril or nifedipine (from 157 ± 21/ (mm Hg/ml/min/100 ml 98 ± 12 to 146 ± 22/90 ± 13 mm Hg and from tissue) 158 ± 25/93 ± 12 to 147 ± 24/86 ± 14, respectively, Relative reduction in FVR 61 ± 14 61 ± 10 ± s.d., P Ͻ 0.01 for changes within both of the during MCh-infusion at groups, no significant difference between the drugs, 4 ␮g/min (%) Table 2). Although baseline FVR was unchanged 1 h Relative reduction in FVR 60 ± 17 64 ± 11 after administration of captopril, the decrease in during SNP-infusion at ␮ FVR induced by MCh (EDV) was significantly 10 g/min (%) potentiated in this treatment group (P Ͻ 0.01 for No significant differences between the two treatment groups con- both doses), while the FVR response to SNP (EIDV) cerning these baseline characteristics were found. MCh, methach- was not significantly changed (Figure 2a). The oline; SNP, sodium-nitroprusside. improvement in MCh-induced vasodilation after Values are expressed as means ± standard deviation (s.d.). captopril administration was significantly correlated to the decrease in MAP induced by the drug decrease in MAP induced by the drug (r =−0.10, (r = 0.72, P Ͻ 0.01, Figure 3). Figure 4).

Nifedipine, short-term effects Captopril, long-term effects One hour after intake of nifedipine, neither baseline Three to 6 months (19 ± 7 weeks) of treatment with FVR, nor the FVR responses to MCh or SNP were captopril induced a significant reduction in BP (SBP significantly altered compared to baseline measure- from 166 ± 36 to 144 ± 18 mm Hg, DBP from 99 ± 8 ments (Figure 2b). There was no significant relation to 86 ± 8 mm Hg, P Ͻ 0.05). Although baseline FVR between the relative change in MCh-induced vaso- was unchanged after long-term treatment, there was dilation after nifedipine administration and the a significant potentiation of the FVR response to MCh compared to the measurements performed before treatment was initiated (Figure 5, P Ͻ 0.05). The decrease in FVR induced by SNP was not sig- nificantly altered by the long-term treatment. No significant changes in FBF in the contralateral control arm were seen in any of the investigations, therefore no adjustment for changes in basal FBF was performed.

Discussion The present study provides further evidence for a defect in EDV in patients with essential hyperten- sion. Furthermore, a positive short-term effect of ACE-inhibition with captopril, but not nifedipine, on EDV in the forearm bed of hypertensive patients despite a similar reduction in BP by the two drugs was shown, in accordance with previous findings.4 Also a withstanding potentiation of EDV by long- Figure 1 The forearm vasodilation in hypertensive patients com- term treatment with captopril was found. Even if the pared to normotensive subjects. ***Denotes P Ͻ 0.0001 vs normo- latter result is based on a small, open pilot study tensive controls. The relative reduction in FVR in hypertensive and therefore the interpretation should be taken patients, n = 23 ({) and in normotensive age- and sex-matched with great caution, the potentiation of EDV was uni- controls, n = 25 (Ǣ). FVR, forearm vascular resistance. MCh, methacholine, a muscarinic agonist inducing endothelium- form throughout the patient group, with some of the dependent vasodilation. SNP, sodium-nitroprusside, a nitric- individuals demonstrating an impressive improve- oxide donor, inducing endothelium-independent vasodilation. ment (16–56%). Anti-hypertensive treatment and endothelial function J Millga˚rd et al 514

Figure 2 The forearm vasodilation before and 1 h after administration of (a) captopril and (b) nifedipine. **Denotes P Ͻ 0.01 vs before administration of captopril. The relative reduction in forearm vascular resistance (FVR) induced by I.A. local infusions of methacholine (MCh), a muscarinic agonist inducing endothelium-dependent vasodilation and sodium-nitroprusside (SNP), a nitric-oxide donor inducing endothelium-independent vasodilation, before ({) and 1 h after (Ǣ) administration of captopril (25 mg), n = 12.

Figure 3 The relation between the improvement in endothelium- Figure 4 The relation between the improvement in endothelium- dependent vasodilation and the reduction in BP 1 h after admin- dependent vasodilation and the reduction in BP 1 h after admin- istration of captopril. The correlation between the relative istration of nifedipine. The non-significant relation between the improvement of forearm endothelium-dependent vasodilation relative improvement of forearm endothelium-dependent vaso- and the reduction in mean artery pressure (MAP) 1 h after admin- dilation and the reduction in mean artery pressure (MAP) 1 h istration of captopril (25 mg). Endothelium-dependent vaso- after administration of nifedipine (10 mg). Endothelium-depen- dilation was induced by methacholine and evaluated as reduction dent vasodilation was induced by methacholine and evaluated as = Ͻ in forearm vascular resistance, r 0.72, P 0.01. reduction in forearm vascular resistance, r = 0.10.

Although Creager et al8 found no positive effect evident that an acute improvement of endothelial on EDV in the forearm circulation by treatment with function in the forearm of hypertensive patients is the ACE-inhibitors captopril and in a achieveable, as previously has been shown.4 It is recent randomised trial in hypertensive patients, the interesting to note that the defect EDV actually nor- longer duration of treatment in the present study (3– malised in the hypertensive patients, since 1 h after 6 months vs 7–8 weeks) might contribute to the posi- captopril administration no significant difference in tive result. In fact, there was a strong, although not EDV between these hypertensive patients and significant, tendency towards a positive relation normotensive subjects could be found. Furthermore, between the treatment duration and the improve- in the patients given captopril, the degree of acute ment in EDV in the present small long-term pilot BP reduction was related to the improvement in study (r = 0.77, not significant). Thus, the encour- EDV, suggesting a close association between the BP aging findings in this pilot study suggests that larger, level and endothelium vasodilator function. randomised trials with a sufficient duration of the However, an acute BP reduction does obviously treatment period are highly warranted to properly not guarantee an improvement in the endothelial evaluate the effects of anti-hypertensive drugs, function, since nifedipine induced a similar especially ACE-inhibitors, on endothelial function. reduction in BP without altering the response to Concerning the short-term effect of captopril, it is either MCh or SNP. This might be interpreted in one Anti-hypertensive treatment and endothelial function J Millga˚rd et al 515 circulating levels of ET-1 have also been lowered by therapy with the ACE-inhibitor captopril in hyper- tensive patients,17 suggesting that a part of the bene- ficial effect of ACE-inhibition on endothelial func- tion might be mediated through ET-1. In addition, concomitant infusion of and ET-1 locally in the forearm blunted the induced by ET-1 infusion only,18 implying that ACE-inhibi- tors also might moderate the effects of ET-1 and not only the formation of this potent vasoconstrictor. Furthermore, ACE-inhibitors are known to increase the levels of , as this vasodilator is degraded by the ACE. As bradykinin is a potent stimulator of NO formation,19 the increased avail- ibility of bradykinin during ACE inhibition would, by increased formation of NO, improve EDV. Fur- thermore, as angiotensin II has been proven to pro- mote production of radicals by stimulation Figure 5 The forearm vasodilation before and after 3–6 months of NADH/NADPH-dependent oxidases,20 ACE- Ͻ of treatment with captopril. *Denotes P 0.05 vs before treat- inhibition may also attenuate the formation of oxy- ment with captopril. The relative reduction in forearm vascular resistance (FVR) induced by I.A. local infusions of methacholine gen radicals and thereby prolong the half-life of NO. (MCh), a muscarinic agonist inducing endothelium-dependent In the present study there was a tendency that vasodilation and sodium-nitroprusside (SNP), a nitric-oxide hypertension also affected EIDV and that treatment donor inducing endothelium-independent vasodilation, before with captopril, both short-term and long-term, also ({) and after (Ǣ) 3–6 months of treatment with captopril, 25 mg twice daily, n = 5. improved EIDV. These tendencies were, however, not significant and it is therefore evident that although the effects of the hypertensive state and of two ways. First, the degree of BP reduction by captopril administration might also affect EIDV to a captopril is of no real importance, but rather an minor degree, the main effects are on EDV. effect of captopril on endothelial function being In conclusion, the present study confirmed that independently related to the BP level. Second, essential hypertension is associated with a defect in nifedipine might directly or indirectly affect EDV in EDV. Furthermore, a significant acute potentiation a way that counteracts any potential beneficial of EDV was seen in hypertensive patients after effects of the reduction in BP. As acute adminis- administration of captopril, but not nifedipine. In tration of nifedipine has been found to stimulate addition, the beneficial efect on EDV seen in a small sympathetic outflow, as evaluated by increased lev- pilot study of long-term treatment with captopril, els of circulating ,14 this effect may would serve as an incitement to perform random- counteract any possible benefit for the endothelium ised, blinded studies to evaluate the long-term induced by the BP reduction. effects of anti-hypertensive treatment on endo- The present study did not investigate possible thelial function. mechanisms mediating the endothelial effect of cap- topril. However, since vasodilation with muscarinic agonists have been shown to require an intact endo- Acknowledgements 13 thelium, and only the response to MCh was affec- This study was supported by grants from the Len- ted by captopril treatment, the mechanisms nanders Foundation and the Selanders Foun- mediating the vascular effect of this ACE-inhibitor dation, Sweden. are most likely endothelium-related. NO and ET-1 are two major endothelium-derived factors respon- sible for vasodilation and constriction,1 both of these References mediators have been suggested to mediate the effects 1 1Lu¨ scher TF, Noll G. The endothelium as a regulator of ACE-inhibition on EDV. of vascular tone and growth. In: Lu¨ sher TF (ed). The A positive local endothelial effect by the ACE- endothelium in . 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