Effect of laparotomy on plasma renin activity in the rabbit

Renal effects of carprofen administered to healthy dogs anesthetized with propofol and isoflurane

OBJECTIVE

To evaluate renal effects of carprofen in healthy dogs following general anesthesia.

DESIGN

Randomized clinical trial.

ANIMALS

10 English hound dogs (6 females and 4 males).

PROCEDURE

Dogs were randomly assigned to control (n = 5) or carprofen (5) groups. Anesthesia was induced with propofol (6 to 8 mg/kg [2.7 to 3.6 mg/lb] of body weight, i.v.) and maintained with isoflurane (end-tidal concentration, 2.0%). Each dog underwent two 60-minute anesthetic episodes with 1 week between episodes, and mean arterial blood pressure was maintained between 60 and 90 mm Hg during each episode. Dogs in the carprofen group received carprofen (2.2 mg/kg [1 mg/lb], p.o.) at 9:00 AM and 6:00 PM the day before and at 7:00 AM the day of the second anesthetic episode. Glomerular filtration rates (GFR) were determined during each anesthetic episode by use of renal scintigraphy. Serum creatinine and BUN concentrations and the urine gamma-glutamyltransferase-to-creatinine concentration (urine GGT:creatinine) ratio were determined daily for 2 days before and 5 days after general anesthesia.

RESULTS

Significant differences were not detected in BUN and serum creatinine concentrations, urine GGT:creatinine ratio, and GFR either between or within treatment groups over time.

CONCLUSIONS AND CLINICAL RELEVANCE

Carprofen did not significantly alter renal function in healthy dogs anesthetized with propofol and isoflurane. These results suggest that carprofen may be safe to use for preemptive perioperative analgesia, provided that normal cardiorespiratory function is maintained.

Differential effect of a selective cyclooxygenase-2 inhibitor versus indomethacin on renal blood flow in conscious volume-depleted dogs

Renal effects of a selective cyclooxygenase-2 (COX-2) inhibitor [MF-Tricyclic; 3-(3,4-difluorophenyl)-4-(4-(methylsulfonyl)phenyl)-2-(5H)-furanone] were studied in control and volume-depleted conscious dogs. MF-Tricyclic was compared with the nonselective COX-1/COX-2 inhibitor indomethacin. Six instrumented male dogs were randomly selected to receive MF-Tricyclic or indomethacin at 10 mg/kg. Volume depletion was effected by a sodium-restricted diet (14 days) with administration of furosemide (7.5 mg/kg, i.v.) the day before the experiment. Indomethacin ablated systemic COX-1 activity (p < 0.05), whereas MF-Tricyclic did not affect this activity. Each compound achieved plasma concentrations in excess of their respective median inhibitory concentrations (IC50 values) against canine COX-2. In controls, neither compound affected mean arterial pressure (MAP), heart rate (HR), renal blood flow (RBF), fractional excretion (FE) Na+, or FE K+. In volume-depleted dogs, indomethacin reduced RBF (p < 0.05), whereas MF-Tricyclic did not affect this parameter. Indices of renal function in volume-depleted dogs were not affected. These data are consistent with the view that the effects of indomethacin on RBF are a consequence of inhibition of COX-1 activity. Furthermore, in these studies, short-term administration of a selective COX-2 inhibitor was without deleterious effects on renal function.

Comparison of a new renin inhibitor and enalaprilat in renal hypertensive dogs

The hypotensive efficacy of a potent new renin inhibitor (N alpha-isovaleryl-L-histidyl-L-prolyl-L-phenylalanyl-L-histidyl-ACHPA+ ++-L- phenylalanyl amide) containing (3S,4S)-4-amino-5-cyclohexyl-3-hydroxy pentanoic acid (ACHPA) was compared with the converting enzyme inhibitor (enalaprilat) (MK-422) in conscious one-kidney dogs before and after tightening a renal artery clamp. Dose-response curves to 0.003 to 0.1 mg/kg/min i.v. infusions of the ACHPA-containing renin inhibitory peptide or enalaprilat (0.003-0.1 mg/kg i.v. bolus) were obtained in one-kidney dogs before and 3 days and 14 days after renal artery constriction. The ACHPA-containing renin inhibitory peptide and enalaprilat maximally decreased blood pressure by 10 +/- 2 and 9 +/- 2 mm Hg before constriction and by 12 +/- 2 and 12 +/- 4 mm Hg in dogs treated 14 days after renal artery constriction, respectively. Glomerular filtration rate and effective renal plasma flow were unaltered or slightly improved. In sharp contrast, both compounds elicited significant, dose-related decreases in blood pressure (-26 +/- 4 and -20 +/- 4 mm Hg, respectively), glomerular filtration rate (-21 +/- 3 and -23 +/- 3 ml/min), and renal plasma flow (-45 +/- 14 and -48 +/- 13 ml/min) in dogs examined 3 days after renal artery constriction. These data demonstrate that ACHPA-containing renin inhibitory peptide and enalaprilat are equally effective antihypertensive agents in dogs with renin-dependent renovascular hypertension and lend credence to the contention that the renin-angiotensin system supports renal function in hypertensive states in which renin levels are elevated.

Effect of total sympathetic blockade on plasma renin activity during surgery

The interaction of sympathetic blockade and decreased mean arterial pressure on plasma renin activity during surgery was studied in dogs. Plasma renin activity was measured during lumbar laminectomy before and after sympathetic blockade produced by subarachnoid spinal anaesthesia. Plasma renin activity was significantly increased during laminectomy. Twenty minutes after sympathetic blockade there were marked decreases in mean arterial pressure and plasma renin activity; but with mean arterial pressure continuing to decline, plasma renin activity showed moderate increases at 50 minutes after sympathetic blockade. It is concluded that increases in plasma renin activity seen during surgical operations can be attenuated by sympathetic blockade produced by subarachnoid or epidural spinal anaesthesia, although decreases in mean arterial pressure resulting from the sympathetic blockade continue to provide a stimulus for renin secretion.

Renin secretion in the chronically perfused pulseless calf. Evidence for failure of stimulation by decreased pulse pressure

To study the influence of arterial pulse pressure on renin release, a chronic pulseless calf preparation was developed using a centrifugal left ventricular bypass blood pump. After pump implantation and recovery, control measurements of renal vein and arterial plasma renin activity, arterial pressure, and renal artery flow were obtained. The centrifugal bypass pump rate then was increased to capture cardiac output completely, and nine conscious calves were perfused in a nonpulsatile manner (pulse pressure less than 5-10 mm Hg) for 48 hours. Nonpulsatile perfusion was well tolerated and serum sodium, potassium, creatinine, and blood urea nitrogen were unchanged during bypass. Mean arterial pressure remained relatively constant [114 +/- 3 (SE) mm Hg] during bypass, and was not significantly changed from control. Although renal blood flow decreased slightly from control (667 +/- 84 ml/min) during the nonpulsatile perfusion period (555 +/- 73 ml/min), renin secretion did not increase significantly from control (482 +/- 81 ng angiotensin I/ml per hr per min) during the bypass period (531 +/- 99). A diurnal cycle of renin secretin was observed during the pulseless perfusions. These data document the lack of any significant stimulatory influence of decreased pulse pressure on renin secretion in a chronic awake calf model.

Contribution of prostaglandins to the renal circulation in conscious, anesthetized, and laparotomized dogs

The effects of an inhibitor of prostaglandin (PG) synthetase, indomethacin, were studied on renal blood flow (RBF) and mean aortic blood pressure (MABP) and related to changes in concentrations of PGs in renal venous blood under widely different experimental conditions. Although levels of PGE-like material ("PGE") in renal venous blood of the chloralose-anesthetized-laparotomized dog were 8-fold greater than in conscious dogs, viz., 0.39 vs. 0.05 ng/ml of blood, respectively, RBF and MABP were similar for each group. Indomethacin in doses as high as 10 mg/kg, iv, affected neither RBF, MABP, nor PG levels either in the conscious dog or in the anesthetized dog. However, in the anesthetized-laparotomized dog, smaller doses of indomethacin (2 mg/kg, iv) decreased RBF by more than 40% and increased MABP by 15%. This was associated with a decline in concentration of renal venous PGs to those levels observed in conscious dogs. The principal renal PG varied according to the experimental conditions. The venous levels of "PGF" were greater than "PGE" in conscious dogs, whereas in acutely stressed dogs the renal venous concentrations of "PGE" were more than 2-fold those of "PGF". Plasma renin activity was highly correlated with "PGE" levels in renal venous blood, but not with "PGF" levels. Thus, in the acutely stressed dog, the renal circulation is supported by a major PG component, withdrawal of which results in a decline in RBF. In contrast, in the conscious dog at rest, renal PGs do not appear to contribute significantly to RBF. The significance of the small basal release of PGs into the renal venous effluent of the conscious dog, which is not affected by indomethacin, remains to be determined.

Peripheral circulation in arterial hypertension

The underlying causes of hypertensive disease remain unclear. This article has attempted to highlight potential dysfunctions in arterial pressure regulation which could either initiate or sustain the hypertensive process. As has been suggested innumerable times hypertension must certainly be a multifactorial abnormality. The current state of knowledge about control of the peripheral circulation in high arterial pressure reinforces the view that interactions between neurogenic, myogenic, humoral, and structural factors are probably disrupted when hypertension appears.

Abolition of the renin-releasing action of frusemide by acute renal denervation in dogs

1. The effects of infusions of frusemide at low (0.05-0.1 mg.kg-1.min-1) and high (0.5-2.0 mg.kg-1.min-1) rates were studied on renin secretion and urinary outputs of sodium and potassium in anaesthetized dogs in which one kidney was removed and the remaining kidney was either innervated or denervated. 2. When the kidney was innervated, low rates of infusion of frusemide did not significantly affect renin secretion if urinary volume and sodium losses were replaced. Without replacement of urinary losses, renin secretion increased at sodium deficits of 0.7-0.9 mmol.kg-1 in the presence of elevated rates of sodium and potassium excretion. 3. High rates of infusion of frusemide caused an immediate increase in renin secretion from innervated kidneys which was not related to urinary losses. 4. Denervation of the kidney increased the urinary outputs of sodium and potassium while it decreased the rate of renin secretion to one-tenth of the resting value. 5. Denervation of the kidney abolished the renin-releasing action of frusemide at both low and high infusion rates even when the sodium deficit amounted to 4.3 mmol.kg-1. 6. Constriction of the aorta producing a fall of 10-30 mmHg in perfusion pressure raised the rate of renin secretion from denervated kidneys to control levels and partially restored the renin-releasing action of frusemide at high infusion rates. 7. The findings indicate that frusemide has a site of action apart from the macula densa in mediating renin release.

Factors influencing plasma renin and angiotensin II in the conscious pregnant ewe and its foetus

1. Plasma renin (measured in the presence of additional substrate) was significantly higher (10.7 +/- 1.1 S.E. of mean ng/ml.hr) in foetal lambs of 111-144 days gestation age (full term 147 days) than in their mothers (1.5 +/- 0.2 ng/ml.hr S.E. of mean, P < 0.001) but plasma angiotensin II concentrations were in the same range (ewe 47.3 +/- 6.6 S.E. of mean, foetus 47.4 +/- 14.1 S.E. of mean pg/ml.). The endogenous velocity of renin production by foetal plasma was also greater than that of maternal plasma.2. Foetal plasma [Na(+)] (137 +/- 0.8 S.E. of mean m-equiv/l.), was lower than that in the ewe (142 +/- 1.5 m-equiv/l. S.E. of mean, P < 0.01).3. Foetal plasma renin in lambs of less than 120 days gestation was lower (9.2 +/- 2.7 S.E. of mean ng/ml.hr) than that in lambs of over 130 days gestation (12.6 +/- 2.6 ng/ml.hr S.E. of mean, P < 0.01). Foetal plasma [K(+)] (3.8 +/- 0.1 S.E. of mean m-equiv/l.) was also lower in lambs of less than 120 days gestation than in those over 130 days (4.1 +/- 0.1 S.E. of mean m-equiv/l., P < 0.001).4. When small volumes of blood (</= 3% of blood volume) were withdrawn from foetal lambs, plasma renin increased. The% increase of plasma renin in hypoxaemic foetal lambs was significantly less (P < 0.05) than in control lambs. At the end of 60 min hypoxaemia, arterial pressure and plasma [K(+)] were significantly higher in hypoxaemic than in control foetal lambs.5. During foetal hypoxaemia, plasma angiotensin II concentration increased concurrently with plasma renin.6. Bilateral nephrectomy was performed in two foetal lambs. Plasma renin fell to very low levels and angiotensin II became undetectable.7. Adrenaline ( approximately .0.42 mug/min.kg I.V.) infused into the foetus did not alter foetal plasma renin. When adrenaline was infused into the ewe ( approximately 0.26 mug/min.kg) maternal plasma renin increased. Maternal infusion of adrenaline raised foetal plasma renin significantly more (P < 0.05) than foetal infusion.8. It is concluded that the foetal kidney is the major source of foetal renin in the last quarter of gestation and that renin release is stimulated by very small reductions of blood volume. Hypoxaemia does not augment renin release and cannot be responsible for high levels of renin and angiotensin associated with vaginal delivery.

Quantification of intermediate steps in the renin-angiotensin-vasoconstrictor feedback loop in the dog

The major intermediate steps in the renin-angiotensin-vasoconstrictor feedback loop have been experimentally determined. The quantitative relationships between renal perfusion pressure, renin secretion, arterial renin activity, and systemic arterial blood pressure were determined in dogs in which the cardiovascular control loops of the central nervous system were eliminated by spinal cord destruction and decapitation. Step-decreases in renal perfusion pressure to a single kidney were introduced and maintained constant to open the feedback loop of arterial pressure. Renin activity was measured by radioimmunoassay of angiotensin I. Each decrease of 15 mm Hg in renal perfusion pressure between pressures of 100 and 50 mm Hg elevated the net secretion of renin nearly 20 ng min -1 g -1 kidney an d the arterial renin activity nearly 7.0 ng ml -1 hour -1 . Renin secretion and arterial renin activity decreased at perfusion pressures below 50 mm Hg. A bioassay procedure for estimating the rate of angiotensin II formation at various increments of arterial renin activity showed that an increase in renin activity of 10 ng ml -1 hour -1 resulted in an increase in the net production of angiotensin II of 5.0 ng kg -1 min -1 . The results of these experiments are useful in predicting alterations in the system that follow a decrease in renal artery pressure, and they clarify interactions of the renin-angiotensin system with other homeostatic pressure-regulating systems.

Renin and acute circulatory renal failure in the rabbit

Plasma renin concentration (PRC) was measured in 25 rabbits before and 6, 24, or 72 hours after subcutaneous injection of glycerol. Renal failure and tubular necrosis developed in most animals and PRC rose sixfold to a maximum at 24 hours. Small insignificant changes of PRC were present at 6 and 72 hours. None of these changes was observed in a control group of nine animals killed 24 hours after an injection of saline. The amount of renin extractable from single superficial glomeruli and from renal cortical tissue was reduced after injection of glycerol. In a second study of 11 anesthetized rabbits, renal venous PRC increased on average from 151 to 1810 units/liter following a 4-hour period of renal artery occlusion. Arterial PRC did not change significantly during this time, but the kidneys showed histological changes of acute tubular necrosis. These experiments are compatible with the suggestion that renin is involved in the pathogenesis of acute circulatory renal failure.

Renin and acute renal failure: studies in man

Plasma renin concentration was increased, usually appreciably, in 22 out of 25 patients with acute renal failure, the average value being 226 units/litre (mean for normal subjects 8.2 units/1.). The highest renin values were found in the first 10 days of the disease; lower and sometimes normal values were found subsequently. Unequivocal acute tubular necrosis was present in only two of the eight cases examined post mortem.These findings are compatible with Goormaghtigh's proposal that an excess of renin and angiotensin may act within the kidney to produce acute renal failure.

The kidneys and arterial pressure in immature and adult rabbits

1. The effect of stepwise haemorrhage on arterial pressure in adult and immature (9-15 days old) rabbits lightly anaesthetized with sodium pentobarbitone is described.2. Bethanidine (1 or 3 mg/kg) lowered initial arterial pressure but did not impair the maintenance of arterial pressure in immature or adult rabbits during stepwise haemorrhage.3. Arterial pressure was only slightly lower in nephrectomized than in intact adult rabbits; in some immature rabbits nephrectomy caused a substantial fall of resting arterial pressure. This fall was largest in animals of low body weight and low haematocrit. Nephrectomy reduced the ability of both immature and adult rabbits to maintain arterial pressure during haemorrhage.4. Arterial pressure fell more precipitately on stepwise haemorrhage in adult rabbits in which the carotid sinus and depressor nerves had been cut than in intact rabbits. No such difference was seen in immature rabbits despite the fact that initial arterial pressure was higher in denervated animals at all ages.5. The responses to stepwise haemorrhage were compared in dummy operated and nephrectomized immature and adult rabbits with carotid sinus and depressor nerves cut to minimize changes of sympathetic tone. Under these conditions the presence or absence of kidneys made no significant difference in the response to stepwise bleeding in adult rabbits. In immature rabbits maintenance of arterial pressure was greatly impaired in the absence of the kidneys.6. The results suggest that a pressor mechanism of renal origin may be relatively more important in the maintenance of arterial pressure in the face of haemorrhage in immature than in adult rabbits.7. Resting arterial pressure in small and anaemic immature rabbits may partly depend on the presence of the kidneys. At birth arterial pressure is higher in rabbits of higher haematocrit but this relationship reverses in the second week of life when the haematocrit level is falling.