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Renal Effects of Theophylline and Caffeine in Newborn Rabbits1

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Renal Effects of Theophylline and Caffeine in Newborn Rabbits1 003 1-399818712 106-06 15$02.00/0 PEDIATRIC RESEARCH Vol. 21, No. 6, 1987 Copyright O 1987 International Pediatric Research Foundation, Inc. Printed in U.S.A. Renal Effects of Theophylline and Caffeine in Newborn Rabbits1 JEAN-BERNARD GOUYON2 AND JEAN-PIERRE GUIGNARD Unite de Nephrologie [J-P.G.], Service de Pediatric, Centre Hospitalier Universitaire Vaudois, 101 1 Lausanne, Switzerland ABSTRACT. Renal hemodynamics and functions were mature infants (1-3). Thus a precise knowledge of their respective assessed in four groups of anaesthetized newborn rabbits adverse renal effects can be helpful for the therapeutic choice. In receiving a single intravenous dose of methylxanthines, i.e.: adult and experimental animals, methylxanthines act as diuretic aminophylline: 3 mg/kg (Al) or 6 mg/kg (A2); sodium and natriuretic agents (4), but conflicting results have been benzoate caffeine: 5 mg/kg (Cl) or 10 mg/kg (C2). Each obtained in several studies assessing the renal effects of theo- animal acted as its own control. The mean PAH extraction phylline in the preterm infant (5). Moreover the renal effects of ratio was not modified by the methylxanthines. Renal blood caffeine have not been extensively investigated in the neonatal flow and glomerular filtration rate were determined by period although some data suggest the absence of gross diuresis clearances of paraaminohippuric acid and inulin, respec- or electrolyte abnormalities (1, 6). Therefore we evaluated the tively. No changes in renal hemodynamics or renal func- acute renal effects of a single dose of theophylline ethylenedi- tions were observed in group Cl. In group C2, renal blood amine (aminophylline, 8 1% theophylline) or sodium benzoate flow and filtration fraction did not vary significantly but caffeine in New Zealand White newborn rabbits whose renal renal vascular resistance showed a delayed increase. Sys- maturation shows close similarities with that of premature infants temic infusion of the two aminophylline regimens induced (7). The methylxanthine doses were selected in the range of the a delayed increase in renal vascular resistance with a usual therapeutic doses used in human neonates (1). concomitant fall in renal blood flow and an increase of filtration fraction in group A2. Glomerular filtration rate was either reduced (3 mg/kg aminophylline) or increased MATERIALS AND METHODS (6 mg/kg aminophylline and 10 mg/kg caffeine). Moreover, Studies were performed in 59 newborn New Zealand rabbits diuresis increased and tubular water reabsorption declined aged 5 to 10 days. Animals were born by spontaneous vaginal in groups Al, A2, and C2. High dose caffeine enhanced delivery and afterward housed with the maternal rabbit and sodium fractional excretion. The acute renal effects of breast-fed. Newborn rabbits were initially anaesthetized with methylxanthines appeared dose- and time-related in im- sodium pentobarbital, 25 mg/kg by intraperitoneal route. Small mature animals and caffeine proved safer than aminophyl- doses of Na pentobarbital were subsequently administered as line at doses used in human neonates. (Pediatr Res 21: necessary. A tracheal cannulation allowed mechanical ventila- 615-618,1987) tion with a mixture of air and oxygen (Rodent ventilator, model 683, Haward, Millis, MA). A stretched PE 10 polyethylene Abbreviations tubing was inserted into the right femoral artery for arterial blood sampling and monitoring of systemic blood pressure. V, urine flow rate A second catheter was similarly placed into the right femoral GFR, glomerular filtration rate vein for solute infusion and drug administration. Surgical pro- MBP, mean blood pressure cedures and vascular cannulations were performed under stereo- RBF, renal blood flow scopic magnifying glass (Zeiss, Oberkochen, Germany). RVR, renal vascular resistance The bladder was catheterized for urine collection in preweighed FF, filtration fraction microtest tubes. During the surgical procedure and subsequent FENa, sodium fractional excretion experimental periods the body temperature of the newborn rab- PAH, para-aminohippuric acid bits was kept at 38-38"5 C using an infrared lamp and a warming Hct, hematocrit operating table. E PAH, renal PAH extraction ratio Throughout the experiment heart rate (Sanborn 780-3 video- U/P.inulin, urine to plasma inulin ratio scope, Hewlett Packard, 78332, Palo Alto, CA), blood pressure MX, methylxanthine (Grass Polygraph, model 7B, Quincy, MA), and esophageal PG, prostaglandin temperature (Digital thermometer, Poliak and Gramiger, EPFL, Lausanne, Switzerland) were continuously recorded. After com- pletion of the surgical procedure priming doses of inulin (100 mg/kg) and PAH (1.25 mg/kg) were administered and a sus- The xanthine derivatives theophylline and caffeine are widely tained infusion was given to maintain constant plasma inulin used and equally effective to control idiopathic apnea in pre- and PAH concentrations. The infusion rate was 1 m1/100 g/h using a constant infusion pump (Perfusor EDL 2, Braun, Mel- Received August 1, 1986; accepted January 22, 1987. sungen, Germany). The infusate contained per liter: 150 mmol Reprint requests Prof. J.-P. Guignard, Uniti de niphrologie, Service de +diatrie, Centre Hospitalier Universitaire Vaudois, 10 11 Lausanne, Switzerland. sodium, 5 mmol potassium, 105 mmol chloride, 50 mmol bicar- Supported by Grant 3.808.0.86 ofthe Swiss National Science Foundation. J.B.G. bonate, 50 g mannitol, 3 g inulin, and 150 mg PAH. About 1 h was Supported-. in .part by. Grant 3.842.0.83 of the Swiss National Science Founda- was merit for animal meparation and 90 min for subsequent tion. equilhration. ~reviousi~we demonstrated that blood ' Presented in part at the Annual Meeting of the Swiss Society of Nephrology, Luzern 1985. heart rate, arterial pH, PO2, PC02, and renal functions remain Present address HBpital d'Enfants de Dijon, 21034 Dijon, Cedex, France. stable for Up to 3 h in this animal preparation (7, 8). 616 GOUYON AN1 D GUIGNARD The experimental protocol successively included a I-h control f 0.6 days; 117 f 7 g. C2: 6.4 + 0.3 days; 108 f 5 g). The mean period (I), the intravenous methylxanthine administration and PAH extraction ratio was similar in untreated (55 + 4%), theo- two I-h study periods (I1 and 111). Blood samples (0.4 ml) were phylline (46 + 7%), and caffeine (48 + 13%) treated rabbits. withdrawn at the midpoint of each urine collection period. Blood Thus RBF, RVR and FF were subsequently calculated assuming gas analysis, hematocrit and protein concentration measure- the same E PAH value (55%) for treated and untreated animals. ments were conducted immediately. The red blood cells were Arterial POz was purposely maintained above 100 mm Hg in reconstituted in human albumin and immediately returned to order to avoid any hypoxemia-induced change in renal hemo- the animal. Plasma and urine samples were kept at 4" C for dynamics (12). No physiological parameters varied significantly subsequent analysis. in groups A1 and A2 (Table 1). As a consequence of repeated A single dose of aminophylline or caffeine diluted in a 100 ~1 blood sampling Hct decreased from period I to period I1 in group saline vehicle was slowly (5 min) infused at the end of period I. C2 and from period I to period I11 in groups C1 and C2 (Table Aminophylline (Euphyllin R, BYK Gulden, Konstanz, Ger- 2). Mean blood pressure, PaC02, arterial pH, and protein levels many; I mg of aminophylline ethylinediamine contains 0.81 mg remained stable throughout the experiments in the caffeine- of theophylline) was administered as follows: 3 mg/kg (group treated animals. Al; n = 8) and 6 mg/kg (group A2; n = 9). Caffeine prepared The changes in absolute V, GFR, RBF, RVR, FF, FENa, and with sodium benzoate was administered as follows: 5 mg/kg U/P inulin ratio values are given in Tables 3 and 4. The following (group C 1; n = 8) and 10 mg/kg (group C2; n = 10). significant percent changes are noteworthy. Group A 1: a decrease Additional experiments were carried out to assess the renal in GFR (-45 + 9%) and RBF (-46 + 8%) associated with an PAH extraction ratio in 15 untreated newborn rabbits, five increase in RVR (+I23 k 45%) in period 111. Group A2: an aminophylline (6 mg/kg) and four caffeine (10 mg/kg) treated increase in GFR (+31 + 6%) in period 11; a decrease in RBF rabbits (1 h after methylxanthines administration). Following a (-37 + 8%) and an increase in RVR (+57 + 18%)in period 111. small laparotomy a fine needle was inserted into the left renal Group C2: an increase in,GFR (+29 + 11%) in period 11; an vein and venous blood was slowly extracted (approximately 0.04 increase in RVR (+36 + 15%) in period 111. ml/min) by a constant extraction pump (Perfusor EDL 2, Braun, Melsungen, Germany). At the end of the experiments the rabbits were killed with a lethal dose of pentobarbital. DISCUSSION The standard clearances (C) of inulin and PAH were calculated Systemic administration of MX to newborn rabbits induced from the formula: changes in GFR and renal hemodynamics in a manner related to the kind and dose of MX and to the time elapsed after MX administration. GFR and renal hemodynamics did not change in the low-dose caffeine group (5 mg/kg). An early increase of where U = urine concentration, P = plasma concentration, V = urine flow rate in ml per min per kg. GFR, RBF, RVR, FF, and GFR was observed after high-dose aminophylline or caffeine and FENa were calculated from the following equations: a delayed decrease after low-dose aminophylline. RVR remained unchanged in rabbits infused with 5 mg/kg caffeine but experi- GFR (ml/kg/min) = C inulin enced a delayed increase with the higher caffeine regimen (10 RBF (ml/kg/min) = C PAH/[E PAH x (1 - Hct)] mg/kg). No significant change in RBF or FF was observed at RVR (mm Hg/ml/kg/min) = blood pressure/RBF either dose of caffeine.
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