The role of angiotensin in the canine renal vascular response to barbiturate anesthesia

Herbal medicine (Oryeongsan) for fluid and sodium balance in renal cortex of spontaneously hypertensive rats

Background

Herbal medicine Oryeongsan (ORS), also known as Wulingsan in Chinesehas been used for the treatment of impaired body fluid balance. However, the mechanisms involved are not clearly defined. The purpose of the present study was to identify the actions of ORS on the renal excretory function and blood pressure (BP) and to define the mechanisms involved in association with renin-angiotensin system (RAS) and natriuretic peptide system (NPS) in spontaneously hypertensive rats (SHR), an animal model of human essential hypertension.

Methods

Changes in urine volume (UV), excretion of electrolytes including Na+ (urinary excretion of Na+ (UNaV)) were measured. RT-PCR was performed to trace the changes in expression of RAS, NPS and sodium (Na+)-hydrogen (H+) exchanger 3 (NHE3) in the renal cortex.

Results

In the SHR treated with vehicle (SHR-V) group, UV and UNaV were suppressed and the Na+ balance was maintained at the higher levels leading to an increase in BP compared to WKY-V group. These were accompanied by an increase in NHE3 expression with an accentuation of angiotensin I converting enzyme-angiotensin II type 1 (ACE-AT1) receptor and concurrent suppression of angiotensin II type 2 (AT2) receptor/ACE2-Mas receptor expression in the renal cortex. Chronic treatment with ORS increased UV and UNaV, and decreased the Na+ and water balance with a decrease in BP in the ORS-treated SHR-ORS group compared to SHR-V. These were accompanied by a decrease in NHE3 expression with a suppression of ACE-AT1 receptor and concurrent accentuation of AT2/ACE2-Mas receptor.

Conclusion

The present study shows that ORS reduced BP with a decrease in Na+ and water retention by a suppression of NHE3 expression via modulation of RAS and NPS in SHR. The present study provides pharmacological rationale for the treatment of hypertension with ORS in SHR.

Pathophysiology of unilateral ischemia-reperfusion injury: importance of renal counterbalance and implications for the AKI-CKD transition

Unilateral ischemia-reperfusion (UIR) injury leads to progressive renal atrophy and tubulointerstitial fibrosis (TIF) and is commonly used to investigate the pathogenesis of the acute kidney injury-chronic kidney disease transition. Although it is well known that contralateral nephrectomy (CNX), even 2 wk post-UIR injury, can improve recovery, the physiological mechanisms and tubular signaling pathways mediating such improved recovery remain poorly defined. Here, we examined the renal hemodynamic and tubular signaling pathways associated with UIR injury and its reversal by CNX. Male Sprague-Dawley rats underwent left UIR or sham UIR and 2 wk later CNX or sham CNX. Blood pressure, left renal blood flow (RBF), and total glomerular filtration rate were assessed in conscious rats for 3 days before and over 2 wk after CNX or sham CNX. In the presence of a contralateral uninjured kidney, left RBF was lower (P < 0.05) from 2 to 4 wk following UIR (3.6 ± 0.3 mL/min) versus sham UIR (9.6 ± 0.3 mL/min). Without CNX, extensive renal atrophy, TIF, and tubule dedifferentiation, but minimal pimonidazole and hypoxia-inducible factor-1α positivity in tubules, were present at 4 wk post-UIR injury. Conversely, CNX led (P < 0.05) to sustained increases in left RBF (6.2 ± 0.6 mL/min) that preceded the increases in glomerular filtration rate. The CNX-induced improvement in renal function was associated with renal hypertrophy, more redifferentiated tubules, less TIF, and robust pimonidazole and hypoxia-inducible factor-1α staining in UIR injured kidneys. Thus, contrary to expectations, indexes of hypoxia are not observed with the extensive TIF at 4 wk post-UIR injury in the absence of CNX but are rather associated with the improved recovery of renal function and structure following CNX.

Effect of extracellular volume expansion and surgical stress on splanchnic blood flow and cardiac output in anesthetized rats: role of nitric oxide

In a normal volume state, surgical stress decreases rather than increases nitric oxide (NO) production in the vascular system. In our studies, the effect of minor and major surgical stress and three different degrees of volume expansion on systemic and splanchnic circulatory parameters and on the NO dependence of the circulation have been investigated. When the degree of volume expansion was increased, cardiac output and organ blood flow increased without significant change in vascular resistances. Major surgical stress reduced the increase in cardiac output and organ blood flow elicited by the volume expansion. NO synthase (NOS) inhibition significantly increased blood pressure and total peripheral resistance (TPR) and decreased cardiac output in all groups of animals. As the degree of volume expansion was increased, the NO dependence of the circulation in the surgically less- and more-stressed animals was inversely influenced in some cases. With the three degrees of volume expansion (20, 40, and 60 ml/kg), the NOS inhibition increased the TPR from 30.7 R/kg +/- 1.90 to 73.6 R/kg +/- 5.00, from 20.7 R/kg +/- 1.43 to 66.7 R/kg +/- 3.88, and from 19.9 R/kg +/- 1.25 to 49.1 R/kg +/- 3.84 in the surgically less-stressed animals and from 38.6 R/kg +/- 2.14 to 59.8 R/kg +/- 5.62, from 31.9 R/kg +/- 2.70 to 81.7 R/kg +/- 9.89, and from 29.1 R/kg +/- 2.49 to 91.1 R/kg +/- 6.36 in the surgically more-stressed animals. Volume expansion increases the NO dependence of the vascular resistance in the surgically more-stressed animals but decreases it in the surgically less-stressed animals.

Hyperglycaemia-induced intrarenal RAS activation: the contribution of metabolic pathways

Hyperglycaemia-induced activation of the renin-angiotensin system (RAS) has been observed in normal and diabetic humans. Our main objective was to determine whether the mechanism involved a physical or metabolic effect of glucose. First, Sprague-Dawley rats of the CD strain were given sequential intravenous (i.v.) doses of 0.01, 0.1, 1.0, and 3.0 mg/kg candesartan 30 minutes apart, in the presence of a continuous i.v. infusion of dextrose 20% in water (D20W). The 0.1 mg/kg dose produced a maximal renal blood flow (RBF) response and was used thereafter. Another set of animals then received an infusion of either normal saline (NS), dextrose 5% in water (D5W) or dextrose 20% in water (D20W) for 2 hours, followed by candesartan 0.1 mg/kg i.v. Finally, the response to candesartan 0.1 mg/kg i.v. during D20W infusion was compared with that during infusion of 2-deoxyglucose (2DG), a glucose analogue that competitively inhibits the glycolytic enzyme, hexokinase. RBF (electromagnetic flowmeter), blood pressure (BP), blood glucose, and urine glucose were monitored. There was no significant RBF response to candesartan on either NS (6.01 to 0.48 to 6.20 to 0.49 ml/minute/g kidney; p=0.216) or D5W (7.63 to 1.20 to 7.58 to 1.39 ml/minute/g kidney; p=0.965), whereas there was a significant response to D20W (6.64 to 0.59 to 7.46 to 0.67 ml/minute/g kidney; p=0.002). The RBF response was significantly enhanced by D20W compared with 2DG (change in RBF: 0.82 to 0.22 vs. -0.04 to 0.26; p=0.05), despite similar BP, blood glucose, and urine glucose. Glucose acts, at least in part, through intracellular utilisation to induce RAS activation, as manifested by an enhanced renal vascular response to an angiotensin II antagonist.

[Changes in renal function induced by anesthesia]

The rate of urine formation and its composition are influenced by the different drugs used during surgery. Anaesthetics act on renal function, not only directly, but also by producing changes in cardiovascular function and in neuroendocrine activity. Many factors may be incriminated: lowered blood pressure and cardiac output, increased sympathetic outflow (renal nerve stimulation and increased plasma catecholamines), increased release of renin, angiotensin and vasopressin. The effects of anaesthetics on the kidney go beyond a simple change in basal haemodynamics and include, for some drugs, an alteration in the ability for the kidney to autoregulate its blood flow and glomerular filtration rate. Studies on toad bladders showed a decrease in transport of water, sodium and organic anions. But, in fact, renal effects of anaesthetics in man and animals depend on the species, the anaesthetic and the method used to study the effect. Most barbiturates and inhalational anaesthetics tend to decrease renal blood flow (RBF) and glomerular filtration rate (GFR). These trends are gradually reversed during recovery. The effects of ketamine and diazepam are not clearly defined. Morphine and fentanyl decrease urine flow and GFR, whilst RBF increases or decreases, depending on whether a direct or indirect measurement technique was used. Muscle relaxants have little effect on renal function. Spinal and epidural anaesthesia only slightly decrease GFR and RBF in proportion to the decrease in mean arterial pressure. Obviously, the preexisting intravascular volume and the quantity of intravenous fluids given strongly influence the renal response to spinal and epidural anaesthesia. Some studies have shown that urine flow rate, creatinine clearance, urinary sodium excretion and RBF are reduced during mechanical ventilation with positive end-expiratory pressure. Surgery itself influences renal function by inducing alterations in prerenal haemodynamics. Operative stress leads to an increase in circulating catecholamines and angiotensin. Significant fluid shifts, excessive blood loss and redistribution of a third space may lead to a prerenal oliguric state, increasing secretion of vasopressin. Acute renal failure (ARF) is a frequently lethal complication of critical surgical illness, due to a variety of factors which interfere with glomerular filtration and tubular reabsorption, such as renal hypoperfusion or nephrotoxic insults. In fact, the initiating aggression ultimately culminates in the development of one or more of the maintenance factors (decreased tubular function, tubular obstruction, decreased GFR and RBF) that reduce urine flow and osmolar excretion. Good management during the perioperative period tends to minimize the risk of developing ARF.

The cardiopulmonary and renal hemodynamic effects of norepinephrine in canine pulmonary embolism

Autologous blood clot was injected into six dogs to produce a graduated decrease in cardiac output (CO). The effects of an infusion of norepinephrine, titrated to specific end points, were recorded before embolization and at two levels of pulmonary hypertension. Simultaneous measurements of systemic and renal hemodynamics were made. Sequential blood clot injection increased (p less than .01) pulmonary vascular resistance (PVR) from 1.3 to 13 to 33 mm Hg.L-1.min and reduced CO 45 percent and 75 percent (p less than .01). Norepinephrine increased both stroke volume and CO (p less than .01) in each condition and did not increase PVR. Since the biventricular filling pressures remained constant or fell slightly with norepinephrine, the increase in CO is best explained by an improvement in pump performance. There was no deterioration in renal blood flow or creatinine clearance with norepinephrine. The data suggested that in this model of right ventricular dysfunction, norepinephrine consistently improved myocardial performance without provoking further vasoconstriction in either the pulmonary or renal circulations.

Renal failure complicating obstructive jaundice

Postoperative acute renal failure in patients with obstructive jaundice remains a clinically significant complication. Acute renal failure occurs in approximately 9 percent of patients requiring surgery for relief of obstructive jaundice, and contributes to eventual mortality in 76 percent of those who develop it. The overall mortality rate for patients undergoing surgery for obstructive jaundice is 16 percent. Despite advances in perioperative care, these figures have changed very little over the past 25 years. This article describes the clinical association between jaundice and renal failure and reviews the studies that have contributed to the delineation of the possible underlying pathophysiologic mechanisms, as well as possible preventive measures which have been developed as a result of these investigations. With increased awareness of the potential risk of developing postoperative acute renal failure, the institution of prophylactic measures may result in an improvement in the mortality rate seen after surgery for obstructive jaundice.

Influence of the renin-angiotensin system on the autoregulation of renal blood flow and glomerular filtration rate in conscious dogs

Renal autoregulation of blood flow (RBF) and glomerular filtration rate (GFR) were examined in 10 conscious foxhounds under a normal sodium diet before and after a continuous intrarenal converting-enzyme inhibition (CEI) or during the application of the angiotensin II antagonist saralasin. In order to prevent alpha-adrenergic interference, phenoxybenzamine was infused into the renal artery. In contrast to studies performed in salt depleted dogs there was no impairment of RBF or GFR autoregulation after CEI or saralasin. Renal blood flow was autoregulated at a level of 3.81 +/- 0.18 ml min-1 g-1 in the control group, 3.98 +/- 0.16 ml min-1 g-1 after CEI and 3.97 +/- 0.41 ml min-1 g-1 after saralasin. The lowest point of autoregulation was very much the same between the individual groups (control: 65.0 +/- 1.4 mmHg; CEI: 66.5 +/- 4.6 mmHg; saralasin: 67.4 +/- 3.2 mm Hg). GFR acted in a similar manner (autoregulation level control: 0.50 +/- 0.03 ml min-1 g-1; CEI: 0.52 +/- 0.05 ml min-1 g-1; saralasin. 0.50 +/- 0.04 ml min-1 g-1). The lowest pressure of GFR autoregulation differed slightly more (control: 81.5 +/- 2.2 mmHg; CEI: 93.2 +/- 4.2 mmHg; saralasin: 85.9 +/- 2.1 mmHg). The results suggest that the renal autoregulation of GFR and RBF is independent of the renin-angiotensin system in conscious dogs during a normal sodium diet.

The effect of captopril on renal blood flow in renal artery stenosis assessed by positron tomography with rubidium-82

The sequence and magnitude of acute changes in renal blood flow following administration of captopril were determined in a canine model of acute unilateral renal artery stenosis using rubidium-82 and positron emission tomography. Data were recorded in each of nine dogs under three conditions: 1) during a baseline control interval, 2) during renal artery stenosis, and 3) during stenosis with intravenous injection of captopril (1.2 mg/kg). Mean arterial blood pressure was 108 +/- 12 mm Hg at control, increased significantly to 125 +/- 13 mm Hg (p less than 0.01) during stenosis, and decreased to 98 +/- 13 mm/Hg (p less than 0.01) after captopril infusion. Mean renal blood flow was calculated using a steady state single compartment model from the images produced by positron emission tomography. The estimated flow to the affected kidney was 3.37 +/- 1.48 ml/min/g at control, 0.86 +/- 0.62 ml/min/g during stenosis (p less than 0.01), and 0.64 +/- 0.57 ml/min/g after captopril administration (p = NS compared with precaptopril value). The estimated flow to the contralateral kidney was minimally reduced from a baseline of 3.84 +/- 0.95 to 3.24 +/- 1.13 ml/min/g (p = NS) during stenosis and increased after captopril infusion (4.08 +/- 0.94 ml/min/g; p = 0.01). These data suggest that repetitive imaging with positron emission tomography can be used to delineate acute changes in renal perfusion following captopril administration.

Autoregulation of renal blood flow, glomerular filtration rate and renin release in conscious dogs

The relationship between renal artery pressure (RAP), renal blood flow (RBF), glomerular filtration rate (GFR) and the renal venous-arterial plasma renin activity difference (PRAD) was studied in 22 chronically instrumented, conscious foxhounds with a daily sodium intake of 6.6 mmol/kg. RAP was reduced in steps and maintained constant for 5 min using an inflatable renal artery cuff and a pressure control system. Between 160 and 81 mm Hg we observed a concomitant autoregulation of GFR and RBF with a high precision. The "break off points" for GRF- and RBF-autoregulation were sharp and were significantly different from each other (GFR: 80.5 +/- 3.5 mm Hg; RBF: 65.6 +/- 1.3 mm Hg; P less than 0.01). In the subautoregulatory range GFR and RBF decreased in a linerar fashion and ceased at 40 and 19 mm Hg, respectively. Between 160 mm Hg and 95 mm Hg (threshold pressure for renin release) PRAD remained unchanged; below threshold pressure PRAD increased steeply (average slope: 0.34 ng AI.ml-1.h-1.mm Hg-1) indicating that resting renin release may be doubled by a fall of RAP by only 3 mm Hg. At the "break-off point" of RBF-autoregulation (66 mm Hg) renin release was 10-fold higher than the resting level. It is concluded that under physiological conditions (normal sodium diet) GFR and RBF are perfectly autoregulated over a wide pressure range. Renin release remains suppressed until RAP falls below a well defined threshold pressure slightly below the animal's resting systemic pressure. RBF is maintained at significantly lower pressures than GFR, indicating that autoregulation of RBF also involves postglomerular vessels.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence against the hypothesis that prostaglandins are the vasodepressor agents of pregnancy. Serial studies in chronically instrumented, conscious rats

Renal hemodynamics increase dramatically during pregnancy, and pressor responsiveness to exogenous administration of vasoconstrictors is attenuated. We investigated whether or not vasodilatory prostaglandins mediate these phenomena. Trained, chronically instrumented, conscious pregnant rats were used. Control values of glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were elevated at midgestation (P less than 0.01 and P = 0.05 from prepregnant means, respectively), and effective renal vascular resistance was decreased (P = 0.05). Indomethacin (4.5-6.5 mg/kg body weight [BW]) failed to decrease renal hemodynamics at this stage of pregnancy; in fact, it raised GFR somewhat further (P less than 0.05). Systemic pressor responsiveness to bolus administration of norepinephrine and angiotensin II (AII) was significantly attenuated by at least gestational day 20. Neither indomethacin (7 mg/kg BW) or meclofenamate (6 mg/kg BW) affected the refractory response. The renal vasculature was also relatively unresponsive to an intravenous infusion of AII (5 ng X kg-1 X min-1) during late gestation (day 19); in particular, the fall in ERPF in response to AII (16 +/- 3%) was markedly less than that observed in the prepregnant condition (34 +/- 3%; P less than 0.05). Indomethacin (6 mg/kg BW) failed to restore this blunted response, and further attenuation was evident, despite the presence of the inhibitor (gestational day 21). We conclude that vasodilatory prostaglandins do not appear to mediate the rise in renal hemodynamics, and the attenuation of the systemic and renal pressor responsiveness observed during pregnancy, insofar as these phenomena were unaffected by acute cyclooxygenase inhibition in unstressed, conscious rats.

Renal vascular responses to saralasin in conscious chemically denervated rabbits and patients with tetraplegia

To determine the relative contributions of direct angiotensin-II-like myotropism and sympathetic nerve stimulation to the partial agonist effect of saralasin, the renal vascular responses to i.v. saralasin (5, 10, 20 micrograms/kg/min) were assessed in normal conscious rabbits before and after sympatholytic treatment with guanethidine (24 mg/kg/day for 9 days) and in 6 chronic tetraplegic patients (0.5, 1, 5 micrograms/kg/min) before and after alpha-adrenoreceptor blockade with i.v. thymoxamine (1 mg/kg/h). In rabbits saralasin reduced effective renal plasma flow (ERPF) and glomerular filtration rate (GFR), and increased renal vascular resistance (RVR) without affecting mean arterial blood pressure (BP). Responses were similar in both groups, but recovery following saralasin was more prolonged after treatment with guanethidine. When 0.1 microgram/kg/min (one fiftieth of the smallest i.v. dose) was infused just proximal to the renal arteries in 4 conscious rabbits (chronically cannulated), renal perfusion fell and RVR increased. In tetraplegics saralasin produced a transient rise in BP and variable increase in RVR; neither response being altered by thymoxamine. These results suggest that saralasin-induced renal vasoconstriction is independent of central and peripheral sympathetic activation, and is probably due to an intrinsic angiotensin-II-like myotropic action.

Preservation of ischemic myocardium by a new converting enzyme inhibitor, enalaprilic acid, in acute myocardial infarction

Enalaprilic acid (MK-422), the biologically active diacid of the converting enzyme inhibitor enalapril, was studied in myocardial ischemia (MI). Acute left coronary artery ligation was produced in 62 male Sprague-Dawley rats, and infarct size was determined by left ventricular free wall (LVFW) creatine kinase (CK) activity. Administration of enalaprilic acid (2 mg/kg) 2 minutes and 24 hours after MI significantly blunted the reduction in LVFW CK activity at 48 hours after ligation, when compared to the MI rats given vehicle (6.4 +/- 0.5 vs 4.7 +/- 0.2 IU/mg protein, respectively; p less than 0.01). The percentage of LVFW spared was significantly (p less than 0.01) increased from 28 +/- 2% to 45 +/- 5% by MK-422. MK-422 also significantly blunted the loss of LVFW CK activity 48 hours after a coronary ligation (10 minutes) followed by reperfusion, when compared to vehicle (10.1 +/- 0.6 vs 8.3 +/- 0.6 IU/mg protein, respectively; p less than 0.05). This represents a significant increase in the percentage of LVFW spared, 65 +/- 5% vs 85 +/- 6% (p less than 0.05). These data indicate a significant protective action afforded by MK-422 in two different protocols of ischemic damage to the myocardium and suggest a role for the renin-angiotensin system in the extension of ischemic damage.

Renal hemodynamics during pregnancy in chronically catheterized, conscious rats

Two types of experiments were performed, cross-sectional and longitudinal. In the cross-sectional studies, rats were mated, later prepared surgically, and then 5 or more days after surgery, each examined twice during days 11 to 15 or days 18 to 20 of gestation. Nonpregnant rats matched for age and prepregnant weight served as controls. In the longitudinal studies, rats were catheterized and, starting 6 days later, examined twice; then the same rats were mated and each was studied on days 5, 8, 12, 16, and 20 of gestation, as well as on day 5 postpartum. In the cross-sectional studies, glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were elevated by approximately 26% and 20%, respectively, above nonpregnant controls at 11 to 15 days of gestation (GFR, 2739 +/- 94 vs. 2181 +/- 134 microliters . min-1, P less than 0.005; ERPF, 9367 +/- 295 vs. 7785 +/- 422 microliters . min-1, P less than 0.01). By 18 to 20 days of gestation, GFR and ERPF had returned to levels that were not significantly different from nonpregnant values. The longitudinal studies confirmed these findings in every respect and further revealed that GFR and ERPF were elevated above nonpregnant values as early as day 5 of gestation (P less than 0.005). Thereafter, they rose to peak values, at 12 and 16 days of gestation, of 3122 +/- 144 and 10,584 +/- 541 microliters . min-1, and then returned to nonpregnant levels by day 20 of gestation.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal hemodynamics in essential and renovascular hypertension. Influence of captopril

Among vascular beds, that of the kidney is especially responsive to angiotensin II, perhaps a reflection of the fact that the renin-angiotensin axis is normally a volume-control rather than a pressure-control system. The dose of angiotensin required to induce renal vasoconstriction in a normal subject receiving a typical, liberal sodium intake, for example, is about an order of magnitude lower than that required to induce a pressor response. Indeed, compelling arguments can be made for a local, intrarenal role as angiotensin's first action in phylogeny, with additional cardiovascular and endocrine responses arising later. In patients with essential hypertension, in whom renal vascular tone is commonly increased, converting enzyme inhibitors such as teprotide and captopril induce a potentiated acute renal vascular response: renal blood flow increases more than it does in normal subjects. The result is a consistent, early increase in sodium excretion and an occasional increase in glomerular filtration rate. Reduced aldosterone release consequent to the block of angiotensin II formation also contributes to the natriuresis and results in positive potassium balance. With long-term therapy, renal function tends to be very well maintained. In renal artery stenosis the situation is more complex: as perfusion pressure distal to the stenosis falls, typically afferent arteriolar dilatation exists and glomerular capillary pressure tends to be maintained by an increase in postglomerular resistance. To the extent that this increase is angiotensin-mediated, suppression of angiotensin formation with captopril can reduce glomerular capillary pressure and thus filtration rate. This is well tolerated in the patient with unilateral stenosis and a healthy contralateral kidney, but can provoke renal failure when the stenosis is bilateral or involves a solitary kidney. The available evidence suggests that the converting enzyme inhibitor's influence on the kidney primarily reflects reduced angiotensin II formation, although reduced kinin degradation or increased prostaglandin synthesis may also have an influence. Whatever the mechanism responsible for the renal response, there are compelling reasons for suspecting that the salutary action of captopril on the kidney makes a substantial contribution to its over-all efficacy in the treatment of hypertension.

Effects of adrenoceptor agonists and antagonists on smooth muscle cells and neuromuscular transmission in the guinea-pig renal artery and vein

In the guinea-pig renal artery and vein, the membrane potential was -66.8 mV and -46.8 mV, the length constant 0.54 mm and 0.43 mm, and the time constant 240 ms and 98 ms, respectively. The maximum slope of the depolarization produced by a 10 fold increase [K]o was 46 mV in the renal artery and 39 mV in the renal vein. Noradrenaline (NA over 5 X 10(-7)M in the artery and over 10(-7)M in the vein) depolarized the membrane and slightly reduced the membrane resistance, assessed from relative changes in the amplitude of electrotonic potential. The action of NA was suppressed by prazosin in the artery but by yohimbine in the vein, i.e. the alpha 1-adrenoceptor is present in the extrajunctional muscle membrane in the renal artery while the alpha 2-adrenoceptor is present in the renal vein. Dopamine and isoprenaline did not modify the membrane properties. In the renal artery, repetitive perivascular nerve stimulation (0.1 ms, 50 Hz, 5 shocks) evoked excitatory junction potential (e.j.p.). Applications of guanethidine (10(-6) M) or tetrodotoxin (3 X 10(-7) M) abolished the generation of the e.j.p.. Low concentrations of phentolamine (5 X 10(-7) M), prazosin (10(-7) M) and yohimbine (5 X 10(-7) M) enhanced the e.j.p. amplitude, while high concentrations of phentolamine (10(-5) M) and prazosin (greater than 10(-5) M) reduced the amplitude of e.j.p.s. NA, dopamine and clonidine consistently suppressed the amplitude of e.j.ps, at any given concentration over 10(-7) M. Spontaneous generated miniature e.j.ps (m.e.j.ps) were recorded on rare occasions. Phentolamine and yohimbine both at 5 x 10(-7) M and prazosin 10(-7) M increased the appearance of m.e.j.ps. 5 In the renal vein, repetitive nerve stimulation failed to generate the e.j.p. Sympathetic innervation to this tissue seems to be sparse. 6 Specificity of innervation and adrenoceptors present on smooth muscle cells in both the renal artery and vein are discussed, and the presynaptic regulation ofNA release is compared with findings in other vascular tissues.

The effects of anesthesia and mode of delivery on the parameters of the renin-angiotensin system

Paired maternal venous (MV) before (P1) and after (P2) general anesthesia, cord venous (CV) and cord arterial (CA) blood was taken from two groups of primagravid women, one delivered vaginally and the other by elective lower segment Caesarian section (ELSCS). ACTH, Cortisol (CoSol) Aldosterone (Aldo) Plasma Renin Activity (PRA) Plasma Renin Concentration (PRC) Angiotensin II (AII) Solium (N alpha) and Potassium [K]+ were measured in both study groups. Of the various hormones studied, all but cortisol were raised in the P2 sample with only ACTH and AII achieving significant increase. A number of significant positive correlations was found between P1 and P2 samples as well as between the hormones themselves. Four of the vaginally delivered group received epidural analgesia and demonstrated significantly higher levels of ACTH and CoSol in the CV sample. A comparison of the studied variables between the two groups showed a significant decrease in the ELSCS group of ACTH and CoSol in the MV sample, of ACTH, CoSol, PRC in the CV sample, and of CoSol in the CA sample. Of all the parameters, studied, only [K]+ together with Aldo was found to be elevated in the CV sample of the ELSCS group but only [K]+ achieved significant increase.

Ketamine hypertension and the renin-angiotensin system

Renin and angiotensin II have been measured before and 10 minutes after anaesthesia, in 23 patients undergoing minor gynaecological surgery. Twelve were anaesthetised with ketamine 2 mg/kg i.v. and the remainder with thiopentone 5-10 mg/kg i.v. Arterial blood pressure was monitored automatically throughout. The arterial blood pressure rose significantly in the group given ketamine and plasma AII concentration fell. In the group given thiopentone there was no significant overall change in blood pressure but an increase in AII. Plasma renin concentration and activity showed significant increases following the administration of ketamine but were unchanged following thiopentone. Overall, there was a significant inverse relationship between the change in blood pressure and the change in AII. This is compatible with a negative feedback being exerted on the renin-angiotensin system by the raised blood pressure, which has itself been evoked by some quite different factor or factors. We conclude that the renin-angiotensin system is not concerned in the pressor response to ketamine.

Renal response to angiotensin-converting enzyme inhibition

Angiotensin-converting enzyme inhibitors, both teprotide and captopril, induce a potentiated renal vascular response in patients with essential hypertension, and with that a consistent increase in sodium excretion and occasionally an increase in glomerular filtration rate. In patients with advanced congestive heart failure resistant to other vasodilators, a similar triad occurs. It is not yet clear in which settings the renal response to angiotensin-converting enzyme inhibition reflects a reduction in angiotensin II formation--thus implicating the renin-angiotensin system in the pathogenesis--or an additional action, such as a potentiation of the local actions of bradykinin or enhanced prostaglandin formation. Under some circumstances, especially where a qualitatively and quantitatively similar response occurs to angiotensin antagonists and angiotensin-converting enzyme inhibitors or where an angiotensin antagonist prevents an additional response to a converting enzyme inhibitor, it is clear that the specific action of the converting enzyme inhibitor on angiotensin II formation is responsible. Unfortunately, for most responses in animal models and all responses in patients, such rigorous evidence is not yet available.

The actions of saralasin on the renal circulation of man and dog; evidence for a sympathetic neural component to vasoconstriction

The mechanism of renal vasoconstriction produced by saralasin and its dependence on the sympathetic nervous system was investigated in subjects with mild essential hypertension and in anaesthetized dogs. Fluid or saline was given to maximize agonist vasoconstrictor responses. The changes in renal haemodynamics produced by intravenously infused saralasin (dose 0.01-10 microgram kg-1 min-1) were assessed by clearance methods. In the patients, it induced a dose-related renal vasoconstriction which correlated with a rise in plasma noradrenaline levels. In dogs with innervated kidneys it also caused vasoconstriction. But in dogs with denervated kidneys it caused vasodilatation. Infusion at the highest dose directly into the renal artery of denervated kidneys induced only vasodilatation. We conclude that one component of the renal vasoconstriction that occurs with intravenous saralasin infusions is mediated by the renal nerves.

Renal function in conscious rats after indomethacin. Evidence for a tubular action of endogenous prostaglandins

1. Conscious rats, with implanted carotid arterial cannulae, received a saline infusion (5.8 ml./hr) via a tail vein for a 6 hr period. The urinary excretion of water, sodium, potassium, urea and the osmolal output were monitored, together with the systemic blood pressure. Glomerular filtration rate (inulin clearance) and effective renal plasma flow (p-aminohippurate clearance) were also measured. Four hours after the start of the infusion, indomethacin (10 mg/kg body weight) in buffered saline, or buffered saline alone, was administered via the tail vein. 2. Following indomethacin administration, urine flow, sodium output and osmolal output were markedly reduced (P less than 0.01). However, there were no measurable changes in the systemic blood pressure, glomerular filtration rate, or effective renal plasma flow. 3. It is concluded that the changes in urinary excretion observed after indomethacin are not dependent on changes in effective renal plasma flow or glomerular filtration, and it is suggested that indomethacin inhibits the synthesis of endogenous prostaglandins which directly influence renal tubular function.

The separate and combined influences of common carotid occlusion and nonhypotensive hemorrhage on kidney blood flow

The separate and combined effects of bilateral common carotid occlusion (C.C.O.) and hemorrhage on renal blood flow (R.B.F.) were studied in 11 unanesthetized dogs. C.C.O. increased arterial blood pressure (4.4 kPa; 33 mm Hg) and heart rate (10 beats/min) while R.B.F. remained unchanged. When kidney perfusion pressure was maintained at its resting level during C.C.O. (implanted pneumatic cuff) there was also no change in R.B.F. After cutting the aortic nerves in 2 dogs the increase in blood pressure and heart rate with C.C.O. was greater (10.6 kPa; 80 mm Hg and 72 beats/min); however, there was no change in R.B.F. A blood loss of 16% (13.6 ml/kg) reduced central venous pressure (0.3 kPa; 2 mm Hg), increased heart rate (8-14 beats/min) and decreased arterial mean pressure by a maximum of 0.7 kPa (5 mm Hg) (non-hypotensive hemorrhage, N.H.H.). R.B.F. showed a tendency to rise and 90 min after the onset of bleeding was slightly increased (12% of control). After N.H.H. carotid occlusion had no effect on R.B.F. when kidney perfusion pressure increased; when perfusion pressure was controlled during C.C.O. the maximum observed decrease of R.B.F. was 15 ml/min (5% of control). It is concluded that the control of R.B.F. during the baroreceptor reflex under normovolemia and after a blood loss of 16% in the conscious dog at rest does not involve sympathetic vasoconstrictor effects which result in a significant change in total blood flow.

Renal function and intrarenal hemodynamics in acutely hypoxic and hypercapnic rats

On the basis of microsphere distribution, inert gas washout, and standard clearance data, the effects of acute hypoxia and hypercapnia on the kidney were studied in anesthetized, mechanically ventilated rats. Moderate hypoxia (mean PO2, 48 mm Hg) did not significantly change diuresis, GFR, and tubular sodium rejection. Due to a decrease in renal vascular resistance (R) from 40.1 to 31.8 mm Hg ml-1 min, mean renal blood flow stayed constant in spite of a significant drop in mean arterial blood pressure. Hypoxic changes in R were not accompanied by significant changes in intrarenal distribution of blood flow (IDBF). In severe hypoxia (PO2 less than 45 mm Hg) with oliguria and marked arterial hypotension, R was the lowest of all groups (28.8 mm Hg ml-1 min). Hypercapnia did not significantly change the renal excretory parameters, although an increase in R (without change in IDBF), together with a decrease in MAP caused a marked drop in mean renal blood flow. From these studies we conclude: 1) in the anestheized rat, acute hypoxia caused significant changes in intrarenal hemodynamics without changes in excretory function, 2) hypoxic renal vasodilation persists even in severe hypotension with oliguria and anuria, 3) in acute hypoxia and hypercapnia, changes in renal blood flow and renal vascular resistance are not accompanied by significant changes in IDBF.

The effects of anesthesia on the excretion of an isotonic saline load in the rat

The ability to excrete a volume of isotonic saline equal to 10% of body weight infused over 60 min, was examined in awake rats and in rats anesthetized with 1 of the 2 agents most commonly used in renal clearance studies, Inactin or Nembutal. Rats anesthetized with Inactin excreted significantly less of the infused sodium during the period of infusion and in the 120-min post-infusion periods as compared to Nembutal-anesthetized rats or awake rats. Following saline infusion, there was a significantly greater decrease in serum protein concentration (25.5 +/- 4.7%) in rats anesthetized with Inactin, compared to that observed in the awake or Nembutal-treated rats. In a separate group of saline-infused awake rats, induction of anesthesia with Inactin resulted in a significant increase in hematocrit and a decrease in serum protein concentration. These studies suggest that Inactin anesthesia decreases the ability of the kidney to excrete a saline load and that, in studies of sodium excretion in the rat, especially if volume expansion is to be part of the experimental protocol, Nembutal rather than Inactin may be the anesthetic of choice.

Sodium nitroprusside-induced hypotension and renal blood flow

Hypotension produced by sodium nitroprusside during halothane anaesthesia in a series of experiments in dogs was accompanied by the maintenance of renal blood flow. Renal blood flow was maintained at levels of systemic pressure at which flow is customarily reduced in man and experimental animals. The significance of this observation is the possibility that sodium nitroprusside has a protective effect on the kidney, not only in states of deliberate hypotension, but in other low flow states where renal perfusion and function may be compromised.

Renal vascular response to interruption of the renin-angiotensin system in normal man

We assessed the role of the renin-angiotensin system in the response of the renal circulation to restriction of sodium intake in 38 normal patients. Both saralasin (10 to 30 ng/kg/min), an angiotensin antagonist, and SQ 20881 (30 to 300microgram/kg), a converting enzyme inhibitor, induced a dose-related increase in renal blood flow (xenon 133 washout) only when the resin-angiotension system was activated by restriction of sodium intake to 10 MEq/day. Increasing doses of saralasin (100 to 1,000 ng/kg/min) reduced renal blood flow, presumably due to the angiotensin-like action of this partial agonist. The renal vascular response to SQ 20881 paralleled the endocrine response: An identical threshold dose (30 microgram/kg) increased renal blood flow and reduced plasma angiotensin II concentration, which fell despite a progressive rise of plasma renin activity. Plasma bradykinin concentration did not change in response to SQ 20881, which also blocks kininase II. Both agents also induced a small but consistent and statistically significant reduction in arterial blood pressure, which will be important in assessing the pathogenetic significance of a blood pressure reduction in patients with hypertension. This study indicates that angiotensin mediates the renal vascular response to restriction of salt intake in normal man and provides an approach to assessing the role played by angiotensin in the pathogenesis of functional renal disease.

Renal blood flow autoregulation and renal venous prostaglandins in the pump-perfused canine kidney (in situ)

1. Renal autoregulation of blood flow was re-examined in the pump-perfused canine kidney and concentrations of prostaglandins E and F in the renal venous plasma were measured by radioimmunoassay. 2. At low perfusion pressures, below the range of autoregulation, prostaglandin E and F concentrations rose and calculated prostaglandin E secretion rate fell. 3. Meclofenamate (10 mg/kg i.v.) reduced renal blood flow and prostaglandin E and F secretion rates, but did not abolish autoregulation. 4. Renal prostaglandins do not appear to mediate autoregulation in the kidney but may affect the level at which flow is controlled.

Shock and the kidney: pathophysiology and pharmacological support

This article reviews current knowledge as to the physiological mechanisms that control renal vascular resistence. The contribution of both extrinsic and intrinsic neuro-humoral regulation of both blood flow and glomerular filtration rate are described. The changes that occur both to the renal blood flow and glomerular filtration rate in the pathophysiological situation of "pre-renal uraemia" as well as "acute tubular necrosis" are described. Within this setting pharmacological manoeuvres that may improve both renal blood flow and glomerular filtration rate are discussed. In addition, the indications for and general principles of haemo-and peritoneal dialysis are described.