ANGIOTENSIN II, NOREPINEPHRINE, AND RENAL TRANSPORT OF ELECTROLYTES AND WATER IN NORMAL MAN AND IN CIRRHOSIS WITH ASCITES

Atrial natriuretic peptide response to ionic and nonionic contrast left ventriculography

Atrial natriuretic peptide (ANP) levels were measured prior to and at 1 and 5 minutes postcontrast left ventriculography with an ionic contrast agent (diatrizoate), and a nonionic agent (iopamidol) and the results were compared. Since ionic contrast agents have been found to cause an increase in left ventricular end-diastolic pressure (LVEDP) and nonionic agents have been found to have less of an effect on LVEDP, we investigated the response of ANP levels, which have been found to increase secondary to increased LVEDP (atrial pressure), with both agents. A group of 38 patients who were scheduled for left heart catheterization for suspected coronary artery disease was included (19 in each group) and blood samples for ANP levels were drawn from the left ventricles. At the same time, heart rate, LVEDP, and left ventricular systolic pressure (LVSP) were also measured. It was found that the LVEDP increased significantly for both agents at 1 minute postventriculography, but no further change occurred at 5 min. Heart rate increased significantly in the diatrizoate group at 1 minute with a return of heart rate to preventriculography levels at 5 min, while the ANP level and LVSP remained unchanged at 1 minute postventriculography with both agents but increased significantly at 5 min in the diatrizoate group only. This difference in ANP response is not correlated with the LVEDP. The response of ANP may be related to heart rate and/or LVSP.

Hepatic circulation: potential for therapeutic intervention

In recent years, knowledge of the physiology and pharmacology of hepatic circulation has grown rapidly. Liver microcirculation has a unique design that allows very efficient exchange processes between plasma and liver cells, even when severe constraints are imposed upon the system, i.e. in stressful situations. Furthermore, it has been recognized recently that sinusoids and their associated cells can no longer be considered only as passive structures ensuring the dispersion of molecules in the liver, but represent a very sophisticated network that protects and regulates parenchymal cells through a variety of mediators. Finally, vascular abnormalities are a prominent feature of a number of liver pathological processes, including cirrhosis and liver cell necrosis whether induced by alcohol, ischemia, endotoxins, virus or chemicals. Although it is not clear whether vascular lesions can be the primary events that lead to hepatocyte injury, the main interest of these findings is that liver microcirculation could represent a potential target for drug action in these conditions.

Role of altered systemic hemodynamics in the blunted renal response to atrial natriuretic peptide in rats with cirrhosis and ascites

The natriuretic effect of pharmacological doses of atrial natriuretic peptide (ANP) is markedly reduced in cirrhosis with ascites. The current study, which includes two protocols, was carried out to investigate whether this phenomenon is related to the altered systemic hemodynamics present in cirrhosis. In protocol A, the administration of ANP (2.5 micrograms.kg-1 as a bolus followed by a constant infusion of 0.1 microgram.kg-1.min-1) to 10 rats with carbon tetrachloride-induced cirrhosis and ascites produced a significantly lower increase in diuresis (13.4 +/- 1.3 microliters/min) and natriuresis (2.3 +/- 0.3 mu Equiv/min) than in 10 control rats (56.3 +/- 1.4 microliters/min and 8.7 +/- 0.5 mu Equiv/min, respectively), indicating a renal resistance to the effect of ANP in this experimental model of cirrhosis. The reduction of arterial pressure induced by ANP was similar in both groups. However, since baseline mean arterial pressure was significantly lower in cirrhotic rats, the degree of hypotension during ANP infusion was also greater in this group of animals (82 +/- 3 vs. 109 +/- 2 mmHg). The aim of protocol B was to assess whether normalization of arterial pressure in cirrhotic rats increases the renal response to ANP. This protocol includes two groups of 10 rats with cirrhosis and ascites infused with a glucose solution containing norepinephrine (CT-NE rats) or angiotensin II (CT-AII rats) at doses to normalize arterial pressure and an additional control group of 10 cirrhotic rats with ascites receiving only glucose solution (CT rats). Angiotensin II, but not norepinephrine or glucose solution administration, was associated with a significant increase in urine volume and sodium excretion. During ANP infusion, CT rats showed a blunted diuretic and natriuretic response. In contrast, the ANP-induced increase in urine volume and sodium excretion observed in CT-NE (53.6 +/- 10.4 microliters/min and 9.3 +/- 2.2 mu Equiv/min) and CT-AII rats (98.3 +/- 11.6 microliters/min and 15.5 +/- 2.9 mu Equiv/m), was similar or even greater than that showed by the healthy rats of protocol A. The degree of hypotension during ANP administration was also similar (CT-NE, 104 +/- 2; CT-AII, 108 +/- 5 mmHg). These results suggest that the blunted response to pharmacological doses of ANP in cirrhosis with ascites is related to altered systemic hemodynamics of cirrhosis, which further deteriorates during the infusion of the peptide.

Portal hypertension ameliorates arterial hypertension in spontaneously hypertensive rats

Systemic hemodynamic effects of portal hypertension in arterial hypertension and their relationship to serum bile acid levels were investigated using spontaneously hypertensive rats 2 and 15 weeks after partial portal vein ligation (SHR-PVL) or sham operation (SHR-SH) and normotensive controls. Mean arterial pressure in SHR-PVL at 2 weeks was decreased to normal due to a decrease in peripheral resistance. Mean arterial pressure and peripheral resistance in SHR-PVL at 15 weeks did not differ from SHR-SH. Resolution of this arterial hypotensive effect and systemic hyperdynamic circulation was associated with decreased portal-systemic shunting. Bile acid levels were increased in both SHR-PVL groups. These results suggest that an endogenous circulating vasodilator(s) associated with portal hypertension ameliorates the systemic vasoconstriction in SHR. Bile acids, while not direct mediators of these hemodynamic events, may be prototypic of this vasodilator. This arterial hypertensive model may aid further investigation of the mechanisms contributing to the hyperdynamic state in portal hypertension.

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.

Renin-angiotensin system in dogs following chronic bile-duct ligation. Relation to vascular reactivity

The pressor response to angiotensin II, blood volume, angiotensin II in arterial blood, renin substrate, renin concentration, renin activity and aldosterone in venous blood, liver function tests, kidney function tests, glucose, sodium, potassium, plasma osmolality and complete blood count were examined before and 1, 2, 3 and 5 weeks after ligation of bile ducts in nine conscious trained dogs. The pressor response to angiotensin II was markedly suppressed after bile-duct ligation, especially at 1-3 weeks postoperation. A maximal decrease in plasma renin substrate, and maximal increases in plasma renin concentration, plasma renin activity and aldosterone were noted at 1 week postoperatively. Plasma angiotensin II levels were elevated at 1 and 5 weeks postoperatively but were near normal 2 weeks postoperatively despite suppression of the angiotensin II pressor response. Endogenous levels did not correlate with suppression of the pressor response to exogenous angiotensin II.

Studies of marked and persistent sodium retention in previously fasted and sodium-deprived obese subjects

To further delineate the effects of fasting and sodium deprivation on the handling of sodium when sodium intake is resumed, balance studies were performed on seven obese female subjects. All subjects underwent a period of total fasting, which continued for 27 to 29 days prior to resumption of sodium intake. Natriuresis in the first week of fasting and continued sodium chloride deprivation resulted in cumulative deficits of 383 +/- 47 mEq (SEM) and 371 +/- 41 mEq of sodium and chloride, respectively. Chloride space decreased from 21.2 +/- 2.7 L to 18.7 +/- 2.5 L, and aldosterone secretory rates (ASR) increased from 43 +/- 13 micrograms/24 h to 597 +/- 138 micrograms/24 h. Following resumption of sodium intake and simultaneous refeeding on low calorie diets in studies on four subjects (group I), cumulative sodium balances during the first seven days ranged from +586 mEq to +1,109 mEq; sodium retained/previously existing sodium deficit = 2.4, 3.2, 2.0, and 1.6 in the four subjects, respectively. Continued sodium retention resulted in cumulative sodium balances ranging from +670 mEq to +1,249 mEq at the end of 19 to 22 days in studies on three subjects whose cumulative sodium balance was +1,249 mEq, sodium retained/sodium deficit = 3.6. During the first five days of sodium intake and refeeding ASR decreased to 74 +/- 26 micrograms/24 h. Sodium chloride administration without refeeding in studies on three subjects (group II) also resulted in retention of more than enough sodium to replenish previously existing sodium deficits.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of captopril on renal function in patients with cirrhosis and ascites

Blockade of angiotensin-converting enzyme has been variously reported to increase or to decrease sodium excretion in patients with cirrhosis and ascites. We administered captopril (50-150 mg) to 11 patients with cirrhosis and ascites to determine the effects on blood pressure, renal blood flow and sodium excretion. Plasma renin activity increased and mean blood pressure fell (by 14 mm Hg). Para-aminohippurate clearances increased from 321 +/- 53 to 559 +/- 83 ml/min (P less than 0.005), but inulin clearances were minimally altered (73 +/- 8 to 76 +/- 7 ml/min), suggesting preferential dilation of glomerular efferent arterioles. Despite unchanged glomerular delivery of sodium, urinary sodium excretion fell in all subjects (from 2.70 +/- 1.00 to 0.48 +/- 0.21 mEq/h), urinary volume was reduced (377 +/- 55 to 182 +/- 42 ml/h, P less than 0.005), and the natriuretic effect of furosemide was blunted. The antinatriuretic effect of captopril may be mediated by reduced angiotensin II-mediated sodium excretion, by decreased prostaglandin production, and/or by indirect effects of reduced blood pressure. Captopril impairs rather than promotes sodium excretion.

Renal hyperemia in portal hypertension is not mediated by gastrointestinal peptides

The objectives of this study were to characterize the time course of development of the renal hyperemia induced by chronic portal vein stenosis (PVS) in the rat, and to assess the possibility that vasoactive blood-borne gastrointestinal peptides mediate the renal hyperemia in established portal hypertension. Blood flow to the kidneys was measured with radioactive microspheres over a ten day time course. On day 2, no difference in renal blood flow (RBF) was observed in PVS rats as compared with controls. However, by day 4, RBF significantly increased by 35% in PVS vs. control animals. On day 6, the renal hyperemia in PVS rats reached a maximal value that was 42% higher than controls. A steady state hyperemia (approximately 40%) was maintained thereafter. Radioimmunoassay of plasma from control and established portal hypertensive rats (10 days samples) revealed that vasoactive intestinal polypeptide, substance P, cholecystokinin, gastrin, neurotensin, pancreatic polypeptide, beta-endorphin and peptide histidine-isoleucine amide are not elevated in arterial plasma of portal hypertensive rats. These data suggest that the renal hyperemia induced by chronic portal vein stenosis is apparent within 4 days of the onset of a hypertensive state and attains a steady state by day 8. Furthermore, at least eight blood-borne gastrointestinal peptides are not directly involved in the renal hyperemia associated with chronic portal hypertension.

Role of renal prostaglandins and the effects of nonsteroidal anti-inflammatory drugs in patients with liver disease

Renal prostaglandins have several key functions in patients with severe liver disease and ascites. Increased activity of vasodilatory prostaglandins counters the underlying impairment in renal perfusion and the effects of vasoactive hormones. Prostaglandins also participate in renin secretion, renal diluting ability, sodium excretion, the action of diuretics, and, possibly, the development of the hepatorenal syndrome. Nonsteroidal anti-inflammatory drugs inhibit these compensatory actions of prostaglandins and cause a functional reduction in glomerular filtration rate and an impairment in sodium and fluid excretion. The severity of these nephrotoxic effects depends on the potency of the drug in inhibiting renal prostaglandins and on patient susceptibility. Patients with ascites and avid sodium retention, sodium-restricted diets, or concurrent diuretic use are most at risk. If nonsteroidal anti-inflammatory drugs must be administered to these patients, the type of drug should be carefully selected and renal function should be closely monitored.

Endocrine mechanisms in congestive cardiac failure. Renin, aldosterone and atrial natriuretic hormone

Overactivity of the renin-angiotensin-aldosterone system occurs in the syndrome of congestive cardiac failure. Aldosterone overactivity is crucially involved in maintaining the oedematous state as evidenced by its often complete correction by adrenalectomy, or by aldosterone antagonists, in both experimental and clinical heart failure. The hyperaldosteronism of heart failure can also be attacked by angiotensin-converting enzyme (ACE) inhibition, which not only blocks the angiotensin drive to aldosterone, but also unloads the heart by blocking renin-angiotensin-mediated vasoconstriction. Accordingly, ACE inhibition alone, if continued in full dosage, can often reduce or obviate the need for daily thiazide diuretic therapy. This specific, two-pronged therapy with fewer side effects emerges as a primary strategy for the treatment of congestive heart failure. To learn more about why and how the renin system becomes involved in heart failure, the renal functional abnormalities have been re-examined. The effects of sodium administration on central haemodynamics and on the activity of the renin system have als been studied. This research has led to a consideration of the role of atrial natriuretic hormone in this pathophysiological interplay. The study recharacterized renal haemodynamic patterns and indicated that in congestive heart failure there is a disproportionate diversion of blood away from the kidneys because of afferent vasoconstriction. However, the glomerular filtration rate is maintained by concurrent efferent arteriolar constriction, expressed by a rising filtration fraction. As heart failure advances, the filtration fraction can no longer rise. At this point, the glomerular filtration rate becomes flow-dependent and falls commensurately with the declining cardiac output. These intrarenal patterns may be mediated in part by increased intrarenal renin activity resulting from heart failure and diuretic therapy. A further study of the abnormal renin system activity operating in heart failure has shown it to be very sensitive to dietary salt intake. Thus, consuming modest amounts of salt (100 mEq/day) was sufficient to markedly suppress renin and aldosterone values. However, since peripheral resistance was not changed, another non-renin, sodium-related mechanism must take over to sustain increased arterial constriction. The fact that captopril challenge evoked no response before and a large response after sodium depletion supports this concept. preliminary data suggest that atrial natriuretic hormone may also be important in congestive heart failure by opposing renin system activity at 4 sites.(ABSTRACT TRUNCATED AT 400 WORDS)

The pathogenesis of renal sodium retention and ascites formation in Laennec's cirrhosis

This chapter critically reviews our current understanding of the pathogenesis, clinical syndrome, and therapy of the disturbances of renal sodium handling, renal perfusion, and glomerular filtration rate that occur in patients with Laennec's cirrhosis. Avid renal sodium reabsorption, a characteristic feature of cirrhosis, occurs independent of moderate changes in renal function and precedes the onset of ascites. The initiation of sodium retention may be a direct consequence of the hepatic disease process and may also result from defective intravascular filling. In the presence of ascites the most important sodium retaining signal is a defective intravascular volume. The principal effectors of renal sodium retention and vasoconstriction are stimulation of the renin-angiotensin-aldosterone axis and augmentation of renal sympathetic nerve activity. Deficient production of natriuretic hormone(s) and endogenous renal vasodilators, such as prostaglandins and kinins, also contributes to the sodium retention and renal hypoperfusion seen in cirrhosis. The hepatorenal syndrome is an extreme imbalance in these renal vasoconstrictor and vasodilator forces. In the therapy of ascites in Laennec's cirrhosis, abstention from alcohol, sodium restriction, and cautious diuresis are the principal therapeutic measures. A grave prognosis accompanies the diagnosis of the hepatorenal syndrome although recoveries have been reported.

Atrial natriuretic hormone, the renin-aldosterone axis, and blood pressure-electrolyte homeostasis

The renin-angiotensin-aldosterone axis exerts major control over sodium and potassium balance and arterial blood pressure. These three functions are continuously regulated by changes in angiotensin II and aldosterone levels in response to wide variations in dietary intake of sodium and potassium. In addition, changes in intrarenal physical factors cause changes in the supply of distal tubular sodium that, in turn, work to determine sodium and potassium excretion and to modulate the release of renal renin. However, certain aspects of sodium homeostasis cannot be fully explained either by the activity of the renin system or by intrarenal physical factors, and this has led investigators to search for other natriuretic hormonal mechanisms. Recently, it has become clear that atrial tissue contains a group of peptides, at least one of which is probably secreted as a regulatory hormone. In animals, these atrial peptides produce immediate, marked natriuresis associated with a rise in glomerular filtration rate (but no alteration of total renal flow) and a simultaneous decrease in arterial blood pressure. Atrial peptides also inhibit renal renin secretion and adrenal cortical secretion of aldosterone, and they oppose the vasoconstrictive action of angiotensin II. One of these atrial peptides may therefore be the long-sought natriuretic hormone, though in a different form and shape than was envisioned. The fact that atrial peptide works to oppose the renin system at four points suggests that this new hormone could have a major complementary role in long-term regulation of blood pressure and electrolyte homeostasis. In this construction the renin system primarily defends sodium balance and blood pressure, with the atrial hormone having an increasing counter-influence in situations involving high blood pressure or sodium surfeit. We can soon expect to learn more about this atrial hormone, including which peptide is the active circulating hormone, what induces or inhibits its release, and what part it plays in cardiovascular diseases.

Decreased pressor reactivity to angiotensin II in cirrhotic rats. Evidence for a post-receptor defect in angiotensin action

We used a model of cirrhosis in the rat, produced by inhalation of carbon tetrachloride for 6 weeks, to investigate the mechanism of resistance to the pressor effects of angiotensin II. The pressor response to angiotensin II was significantly lower in conscious cirrhotic animals than in controls. On the other hand, cirrhotic animals had normal pressor responses to norepinephrine, indicating that a generalized defect in vascular reactivity does not cause the decreased pressor response to angiotensin II. Enhanced baroreceptor activity was not the cause of the decreased pressor response to angiotensin II, since baroreflex control of heart rate after angiotensin II was similar in cirrhotics and controls. Pretreatment with either the converting enzyme inhibitor captopril to reduce circulating angiotensin II or the prostaglandin synthesis inhibitor meclofenamate failed to normalize the response to angiotensin II. Thus, neither prior occupancy of receptors with endogenous angiotensin II nor the production of vasodilatory prostaglandins was responsible for the decreased angiotensin II response. Studies of angiotensin II binding by mesenteric artery smooth muscle particles showed that, in cirrhotic animals, receptor affinity for angiotensin II, was significantly lower than in controls (kd: cirrhosis 1.11 +/- 0.09 nM, control 0.94 +/- 0.13 nM; P less than 0.02), whereas receptor number was significantly increased (cirrhosis 315 +/- 42 fmol/mg protein, control 277 +/- 43 fmol/mg protein, P less than 0.01). However, total binding of AII by vascular receptors from cirrhotics was no different than in controls, since the decrease in affinity negated the increase in receptor number.(ABSTRACT TRUNCATED AT 250 WORDS)

Interrelationship between cardiac output and vascular resistance as determinants of effective arterial blood volume in cirrhotic patients

The effect of head-out water immersion (HWI) in decompensated cirrhotic patients to correct sodium and water excretion has been found to be incomplete and variable. The explanation may be that the efficacy of HWI in correcting a decreased effective arterial blood volume (EABV) in decompensated cirrhotic patients is limited by an accompanying decrease in systemic vascular resistance (SVR) and thus a relative increase in arterial vascular holding capacity. The present studies were undertaken to examine this possibility by maintaining SVR (dynes X sec X cm-5) nearly constant during HWI with an exogenous infusion of norepinephrine (HWI + NE). In six decompensated cirrhotic patients, neither HWI nor NE infusion alone significantly increased sodium excretion (UNaV, 13 vs. 19 and 13 microEq/min, respectively), but each maneuver increased the excretion of a 20 ml/kg water load (28 to 60 and 61%, respectively, both P less than 0.05). The combination of HWI + NE, however, significantly increased UNaV to 70 microEq/min (P less than 0.05) and percentage of water excretion to 95 (P less than 0.001), values significantly greater than those achieved with either maneuver alone. These differences were not explained by any changes in inulin clearance. With HWI alone, cardiac index (CI) increased (4.2 to 5.3 liter/min/m2, P less than 0.01), but SVR decreased (872 to 613 dynes X sec X cm-5, P less than 0.001) and mean arterial pressure (MAP) remained constant (83 vs. 78 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

The renin system for long-term control over vasoconstriction and sodium-volume homeostasis in the spectrum of hypertension: three new frontiers in research

This morning I have presented something old and something new and I have tried to point out what I think are some promising areas of current research. In the past two decades we have made great strides in our understanding of hypertensive mechanisms. We now know that essential hypertension can no longer be viewed an a single entity. Its heterogeneity in renin patterns is matched by heterogeneity in response or lack of response of individual patients to different types of drugs, and by heterogeneity in risk and prognosis. Analysis of renin system patterns has proven to be very productive for enabling us to understand the participation of the vasoconstriction or volume factors that inevitability work to maintain all hypertensive states. This bipolar analysis of hypertensive phenomena in turn has led to better diagnosis and to more specific treatment of individual patients. In our present state of knowledge, we still need to understand why the renin system so often inappropriately participates in maintenance or causation of the hypertensive state and why it fails to turn itself off in medium or high renin patients. In the low renin patients we do not understand why renal sodium retention occurs nor how it produces sustained increases in peripheral resistance. Three of many potentially exciting areas for expanding our knowledge are the prorenin problem, the natriuretic hormone problem, and the recently discovered relationships between the divalent cations, calcium and magnesium, and the concurrent renin system patterns in the renin subgroups of essential hypertension. Perhaps one of these areas will serve as an appetizer for the participants here today, and in particular for the man we honor, Franz Gross.

Cardiovascular responsiveness to vasoactive agents in rats with obstructive jaundice

1. Pressor responses to tyramine, beta-phenylethylamine and angiotensin II were normal in urethane-anaesthetized rats 7 days after division of the common bile duct. The pressor response to noradrenaline was enhanced at the highest dose level used. 2. The hypotensive response to haemorrhage was exaggerated in bile duct divided rats. 3. The exaggerated haemorrhagic hypotension of bile duct divided rats is unlikely to be the result of impaired vascular response to noradrenaline or angiotensin II, or of accumulation of false neurotransmitters by sympathetic nerves.

Pathogenesis of sodium and water retention in edematous disorders

Edema is a collection of fluid within the body's interstitial space which occurs when there is an alteration of the Starling forces which control transfer of fluid from the vascular compartment to surrounding tissue spaces. Generalized edema results when altered Starling forces affect all capillary beds, such as occurs in cardiac failure, cirrhosis, and nephrotic syndrome. Common to these conditions is the development of increased total body sodium and water content. The kidneys play an essential role in the retention of this sodium and water. In this article we shall discuss the signals the kidneys receive for sodium and water retention in these edematous disorders (afferent mechanisms). We shall also examine the means by which the kidney responds to these signals and retains sodium and water (efferent mechanisms). As shall become apparent these edematous states may share many of the same afferent and efferent mechanisms for sodium and water retention.

Angiotensin-induced sodium excretion patterns in cirrhosis: role of renal prostaglandins

Changes in renal hemodynamics and sodium excretion induced by an angiotensin II (AII) infusion were correlated with urinary prostaglandin E2 (PGE2) excretion in 15 patients with cirrhosis and ascites. All induced natriuretic responses in 47% and antinatriuretic responses in 53% of the patients. Natriuresis was accompanied by an increase; antinatriuresis by a decrease in PGE2 excretion. Although there was no change in GFR (CIn), renal blood flow (CPAH) decreased. Patients were clinically indistinguishable. Antinatriuretic responders tended, however, to have higher baseline PGE2 excretion rates, were more sensitive to effects of prostaglandin blockade, and were less sensitive to the pressor effect of AII. Following partial inhibition of renal prostaglandin synthesis by indomethacin, AII-induced natriuretic responses were accentuated. GFR, RBF, and urine flow rate markedly decreased in both groups. There was no difference in pressor sensitivity to AII following prostaglandin synthesis blockade. We conclude that in patients with hepatic cirrhosis, the sodium excretion pattern induced by an exogenous AII challenge may depend on the prior state of intrarenal prostaglandin activity. Our findings also support the hypothesis that renal hemodynamic parameters in patients with cirrhosis and ascites are crucially dependent on renal prostaglandins.

The renin system for understanding human hypertension: evidence for blood pressure control by a bipolar vasoconstriction-volume mechanism. Prorenin as a determinant of renin secretion

A body of evidence indicates that all hypertensive phenomena ranging from mild disorders to fulminant malignant hypertension can be profitably analyzed by assessing the relative contribution of two final determinants of the arterial blood pressure--the degree of arteriolar vasoconstriction and size of the volume filling the arterial tree. The latter function is largely determined by the state of sodium balance. Renin-sodium profiling and separate testing with specific pharmacologic probes are the basic tools for quantifying these factors in individual patients. This bidimensional analysis of blood pressure phenomena has considerable practical value for identifying and treating curable renovascular and adrenocortical forms. Beyond this, the analysis provides pathophysiologic information of practical value for characterizing and treating individual patients in the whole spectrum of human hypertensive diseases including essential hypertension. This new analytical scaffold also identifies key physiologic questions for future research. About 90 percent of the circulating renin occurs in an inactive form as a possible prorenin, which could be an important regulatory point for renin release. In response to stimuli prorenin rises and falls with active renin. Beta blockade may lower active renin by blocking the conversion process. At the physiological level the activation and/or release of renin appears to be primarily determined by sodium-volume changes perceived by a distal tubular mechanism.

Factors influencing vascular hyporesponsiveness to angiotensin II

Bartter's syndrome is characterized, in part, by hyporesponsiveness to the pressor effect of exogenous angiotensin II (AII). This has been attributed to volume contraction, hypokalemia, and/or increased prostaglandin (PG) levels. In order to investigate factors responsible for a diminished response to the pressor effect of AII, rats were made hypokalemic or volume contracted and hypokalemic (VCHK) by dietary restriction. AII sensitivity was examined by determining the dose of AII required to raise the mean arterial pressure 20 mm Hg. When compared with control rats. VCHK and hypokalemic rats were significantly less sensitive to AII. VCHK rats were significantly less sensitive to AII than hypokalemic rats. Both experimental groups were similarly hypokalemic, but plasma renin activity (PRA) of VCHK only was greater than control values. In VCHK rats, acute K+ restoration partially corrected AII hyporesponsiveness, although plasma K+ increased to normal. In VCHK rats, acute volume expansion with normal saline similarly achieved only partial correction of AII hyporesponsiveness although PRA values fell to the control range. Simultaneous K+ restoration and volume expansion to VCHK rats successfully restored AII sensitivity to the control range. Dietary sodium, chloride, and potassium restriction did not increase urinary excretion to PGE2. Indomethacin (5 mg/kg, iv) given acutely to VCHK rats did not significantly after baseline hyporesponsiveness to AII. Norepinephrine vascular sensitivity was not affected by either volume contraction or hypokalemia. These data demonstrate that volume contraction and hypokalemia individually depress exogenous AII sensitivity in the rat and do so by separate and additive mechanisms. Furthermore, these mechanisms appear to be independent of PG.

Effect of endogenous angiotensin on the efferent glomerular arteriole of rat kidney

The local, direct effect of endogenous angiotensin II (AII) in the isolated, perfused rat kidney was studied in an "open-circuit," single-pass preparation perfused at a constant pressure with an artificial solution containing 6.5% bovine albumin in Krebs-Ringer solution. After the addition of purified renin substrate (tetradecapeptide, 3 to 5 X 10(-8) M), renal plasma flow fell from 25.3 +/- 1.6 to 14.4 +/- 1.0 ml x min-1 (N = 6, P < 0.001) and GFR rose from 0.3 +/- 0.03 to 0.63 +/- 0.06 ml.min-1 (P < 0.001). Filtration fraction rose accordingly from 0.015 +/- 0.001 to 0.044 +/- 0.002 (P < 0.001). The effects of the renin substrate were promptly reversed by the addition of an angiotensin antagonist, Sar1-Al8-AII (3 X 10(-6) M). Measurements of distribution of perfusate flow between outer and inner cortex were made with radioactive microspheres. Outer cortical flow was 75.3 +/- 3.5% of the total cortical flow during the control periods and 73.7 +/- 2.3% during the maximal renin substrate effect. We conclude that endogenous AII is active locally, independent of systemic recirculation. Its major site of action in this preparation is on the efferent glomerular arteriole.

Renin-angiotensin-aldosterone system in cirrhosis

According to traditional concepts, ascites formation and portal hypertension in cirrhosis lead to a deficit in the 'effective' extracellular fluid (ECF) and blood volumes respectively. The renin-angiotensin-aldosterone (RAA) system is thus stimulated and the kidneys retain fluid as a homeostatic mechanism to restore the ECF and blood volumes. Recent studies, however, show that approximately two-thirds of patients with ascites do not have a stimulated RAA system and in those without clinical evidence of fluid retention the RAA system is actually suppressed. These findings are incompatible with the concepts of reduced effective ECF and blood volumes. Despite the fact that most patients retaining sodim and accumulating ascites have a normal plasma aldosterone concentration, other evidence strongly suggests a dominant role for aldosterone in the regulation of renal sodium excretion. There might therefore be an increased renal tubular sensitivity to aldosterone in cirrhosis. For the one-third of patients with ascites who do have a stimulated RAA system this may well be a response to reduced effective ECF and/or blood volumes in accord with traditional concepts.

Diuretic-induced renal impairment without volume depletion in cirrhosis: changes in the renin-angiotensin system and the effect of beta-adrenergic blockade

In 4 patients with cirrhosis and ascites, diuretic therapy resulted in an impairment of renal function that was associated with a rise in plasma renin activity (PRA). In 3, this occurred in the absence of volume depletion. When diuretics were discontinued, renal function returned to normal. beta-adrenergic blocking drugs were then given to suppress renin secretion and diuretics restarted. On this occasion, impairment of renal function did not occur. In 2 further patients, administration of beta-adrenergic blockers during a period of diuretic-induced renal impairment resulted in an improvement in renal function. Although these findings may indicate that diuretic-induced renal impairment in cirrhosis is at least partly due to activation of the renin-angiotensin system, in another group of patients a diuretic-induced rise in PRA was not associated with a deterioration in renal function.

Changes in plasma renin activity in cirrhosis: a reappraisal based on studies in 67 patients and "low-renin" cirrhosis

The generally held views that plasma renin activity (PRA) is increased in cirrhosis and that this is secondary to reductions in the "effective" blood or extracellular fluid (ECF) volumes, consequent on the effects of portal hypertension, were re-examined in the present study. Measurements of PRA in 67 patients representing different clinical stages of cirrhosis showed that the mean value in 15 patients without ascites was significantly reduced. In 21 of 35 with ascites, PRA was either reduced or within the normal range. A low plasma renin substrate concentration was not the cause for the low PRA. These findings are not in keeping with the concepts of reduced "effective" blood or ECF volumes at least for the majority of patients at these stages of cirrhosis under the conditions of the present study. The only group showing a significantly increased PRA had evidence of renal impairment. In these 17 patients the underlying reduction in renal perfusion may have been the stimulus to the kidney that led to an increase to renin secretion.

Renal hemodynamics and the renin--angiotensin system in cirrhosis: relationship to sodium retention

Renal hemodynamics and the renin-angiotensin-aldosterone system were investigated in 15 cirrhotic patients without renal failure on controlled sodium intake of 140-160 mEq/day and related to the degree of sodium retention as measured by urinary sodium excretion. Fourteen patients were free of clinical ascites when studied. The distribution of renal blood flow was measured by the noninvasive technique of computerized radioisotope renography. In 11 patients, outer cortical renal plasma flow, expressed as a percentage of total effective renal plasma flow, was directly proportional to sodium excretion (P less than or equal to 0.01). Three patients with severe sodium retention (UNa.V less than or equal to 10 mEq) had estimated outer cortical renal plasma flows of less than or equal to 274 ml/min/1.73 M2 as compared to eight cirrhotics with better (UNa.V greater than or equal to 50 mEq) sodium tolerance (mean = 438 ml/min/1.73 M2). A significant inverse correlation (P less than or equal to 0.01) existed between outer renal cortical blood flow and plasma renin activity. No significant relationship was observed between glomerular filtration rate, total effective renal plasma flow, plasma aldosterone concentration and sodium excretion. These results provide further evidence that a renal vascular abnormality exists in cirrhosis, and that diminished outer cortical renal perfusion is related to the elevated renin levels and sodium intolerance observed in cirrhotic patients.

The effect of altered sodium balance upon renal vascular reactivity to angiotensin II and norepinephrine in the dog. Mechanism of variation in angiotensin responses

The mechanism whereby the vasoconstrictor response to angiotensin II (AII) is influenced by sodium balance or disease is unclear. To explore this question, the renal vascular responses (RVR) to intrarenal injections of subpressor doses of AII and norepinephrine were studied in dogs with an electromagnetic flowmeter. Acute and chronic sodium depletion increased plasma renin activity (PRA) and blunted the RVR to AII, while acute sodium repletion and chronic sodium excess plus desoxycorticosterone acetate decreased PRA and enhanced the RVR to AII. The magnitude of the RVR to AII was inversely related to PRA. The RVR to norepinephrine was unaffected by sodium balance and was not related to PRA. Inhibition of the conversion of angiotensin I to AII by SQ 20,881 during sodium depletion lowered mean arterial blood pressure (MABP), increased renal blood flow (RBF), and enhanced the RVR to AII but not to norepinephrine. Administration of bradykinin to chronically sodium-depleted dogs also lowered the MABP and increased RBF but had no effect on the RVR to AII. SQ 20,881 had no effect on MABP, RBF, or the RVR to AII in the dogs with chronic sodium excess and desoxycorticosterone acetate. Administration of indomethacin to chronically sodium-depleted dogs lowered RBF but did not influence the RVR to AII. The results indicate that the RVR to AII is selectively influenced by sodium balance and that the magnitude of the response is inversely related to the availability of endogenous AII. The data did not suggest that the variations in the RVR to AII were because of direct effects of sodium on vascular contraction, changes in the number of vascular AII receptors, or the renal prostaglandins. The results are consistent with the hypothesis that the vasoconstrictor effect of AII in the renal vasculature is primarily dependent upon the degree to which the AII vascular receptors are occupied by endogenous hormone.

Angiotensin antagonists with increased specificity for the renal vasculature

This study was designed to ascertain whether renal vascular angiotensin receptors differ from other systemic angiotensin receptors and whether, on that basis, antagonists with greater specificity for the renal vasculature can be defined. Femoral and renal blood flow and their responses to angiotensin II (AII) and its heptapeptide analogue, 1-des Asp AII (AIII), were measured with an electromagnetic flowmeter in 26 dogs. For the kidney, the threshold doses of AII and AIII were identical (2.5+/-0.27 vs. 2.3+/-0.35 pmol/100 ml renal blood flow, with similar dose-response curves. In contrast, AII had a greater pressor effect (P less than 0.001) and produced more femoral vasoconstriction (P less than 0.001) than AIII. All four antagonists studied (1-Sar, 8-Ala AII [P113]; 8-Ala AII; 1-des Asp, 8-Ala AII; 1-des Asp, 8-Ile AII) induced parallel shifts in the renal blood flow response to AII and AIII. P113 induced greater blockade than 8-Ala AII (P less than 0.001) which, in turn, was more effective than 1-des Asp, 8-Ala AII (P less than 0.001). 1-des Asp, 8-Ile AII was as effective as P113. Each analogue induced an identical inhibition of the renal vascular response to AII and AIII. In addition, AII and AIII induced cross-tachyphylaxis. All lines of evidence suggested that AII and AIII act on a single receptor in the kidney, which differs at least functionally from other systemic vascular receptors. The possibility that heptapeptide analogues represent angiotensin antagonists with greater specificity for the renal vasculature was pursued in a model in which the renin-angiotensin system is activated. Acute, partial thoracic inferior vena caval occlusion was induced in an additional 16 dogs. P113 induced progressive, dose-related hypotension and a limited increase in renal blood flow in this model. The 1-des Asp, 8-Ile AII analogue, conversely, induced a consistent, larger, dose-related renal blood flow increase, with significantly less hypotension over a wide dose range. We conclude that the renal vascular receptor differs sufficiently from systemic angiotensin receptors that heptapeptide analogues of AII will be useful in exploring angiotensin's role in states characterized by disordered renal perfusion and function.

Effect of angiotensin on normal renal circulation determined by angiography and a dye dilution technique

Angiotensin in a dose of 0.5 to 1.0 microgran injected into the renal artery of healthy kidneys initially decreased renal blood flow and increased the appearance time and mean transit time of dye and contrast medium as examined by a dye dilution technique and angiography. The initial phase is followed by a reactive hyperemia. The increased vascular resistance is probably localized peripherally on the arterial side of the vascular tree. Optimum dose is 0.5 to 1.0 microgram angiotensin in diagnosis of renal tumours. Optimum interval between drug administration and angiography is 10 to 60 s.

Vascular angiotensin receptors and their role in blood pressure control

The renin angiotensin system has an important role in regulating arterial blood pressure in homeostasis and disease. A reciprocal relationship exists between sodium balance and the circulating levels of renin and angiotensin II. The vascular responsiveness to angiotensin II, the major vasconstrictor component of the renal pressor system, can be impaired by numerous factors including sodium depletion or a reduction in effective plasma volume. In situations in which the renin-angiotensin system is activated, a negative relationship between the angiotensin II pressor response and the circulating angiotensin II level is observed. This effect seems to involve a change of the angiotensin II receptor interaction in the vascular smooth muscle. The prevention of angiotensin II generation by the inhibition of converting enzyme causes an immediate increase in the pressor response to angiotensin; after bilateral nephrectomy, it takes much longer to develop. In addition, the depressor response to angiotensin antagnoists and converting enzyme inhibitor is preserved after bilateral nephrectomy for much longer periods than can be accounted for by the disappearance of circulating renin. These observations support the view that the decrease in vascular response to angiotensin II during sodium deprivation or when body fluid volumes are reduced is the result of prior occupancy of the receptor sites by endogenous hormone generated both in the plasma and locally within blood vessel walls. Therefore, a change in the number or affinity of receptors consequent to a change in sodium balance or as a modulating function of the renin-angiotensin system need not be postulated to explain changes in angiotensin vascular responsiveness.

Effect of blockade of angiotensin II on blood pressure, renin and aldosterone in cirrhosis

1-Sar-8-ala angiotensin II (saralasin) was infused intravenously in graded doses of from 0.1 to 10 mug/kg/min to five patients with cirrhosis and ascites after three days of restricted sodium intake. In each patient blockade of AII by saralasin produced a marked fall in blood pressure, a rise in plasma renin activity (PRA) and plasma renin concentration (PRC) and, in four of the five, a fall in plasma aldosterone (PA). The rise in PRA and PRC correlated poorly with changes in blood pressure. The effects of saralasin rapidly reversed after cessation of the infusion. Plasma volume was normal or high in each case. Three patients were mildly hypotensive in the control state, and all five were resistant to the pressor effect of infused AII. After three days of salt loading, the above effects of saralasin were diminished but not abolished. In four normal subjects, after salt depletion, saralasin infusion induced qualitatively similar but much smaller changes in blood pressure, PRA and PRC. In two cirrhotic patients without ascites, after salt depletion, saralasin infusion caused a rise in blood pressure with no significant changes in PRA, PRC or PA. These results provide evidence that in patients with cirrhosis and ascites circulating AII is active in support of blood pressure, in direct suppression of renal renin release, and in stimulation of aldosterone release.

Agonist and antagonist effects of Sar1-ala8--angiotensin II in salt-loaded and salt-depleted normal man

1 Three normal subjects were infused with Sar1-ala8-angiotensin II (Saralasin, P113) whilst on a high sodium (200 mEq + normal diet) and a low sodium (10 mEq diet) intake. 2 On the high sodium intake when angiotensin II and plasma renin activity (PRA) were suppressed, P113 infusion (5-10 mug kg-1 min-1) caused a slight rise in BP and a marked drop in urine flow and sodium excretion, with a fall in glomerular filtration rate, and effective renal plasma flow. 3 On the low sodium intake, when angiotensin II and PRA were increased, P113 infusion (5-10 mugkg-1 min-1) caused no change in blood pressure, urine flow or sodium excretion. However, when P113 was infused at an incremental rate starting at 0.25 mug kg-1 min-1 there was a fall in standing BP, which was maximal at an infusion rate of 1 mug kg-1 min-1, and this fall in standing BP was largely abolished as the rate of infusion was increased to 10 mug kg-1 min -1. 4 These results show firstly that angiotension II is involved in maintaning standing blood pressure during dietary sodium depletion in normal man and secondly that P113 does have agonist as well as antagonist activity in normal man, the effect depending on the level of angiotension II and sodium intake. When looking for angiotensin II mediated hypertension it may ne important to use an incremental rate of infusion of P113 as the agonist activity of larger doses may mask its hypotensive action.

Hepatorenal syndrome: a disease mediated by the intrarenal action of renin

The functional renal failure accompanying advanced liver disease is characterized by azotemia, a urine of very low sodium concentration and systemic hypotension with decreased renal perfusion and high renal vascular resistance. Patients with this disorder have a markedly reduced ability to excrete free water and develop hyponatremia, ascites and edema. It is postulated that this renal dysfunction is due to hepatic failure to make renin substrate. Renin released from the kidney is thus unable to exert its pressor effect. The resultant hypotension and renal hypoperfusion continue to stimulate excessive synthesis and release of renin. It is postulated that the overdriven renal renin system increases renovascular resistance at the level of the glomerular arterioles. This causes decreased renal blood flow and decreased glomerular filtration rate leading to salt and water retention and azotemia. Since no renin substrate is available for human infusion, this hypothesis could be tested either by infusion of angiotensin II to restore systemic blood pressure and renal perfusion or by beta adrenergic blockade with propranolol to attempt to decrease the intrarenal effects of renin, restore glomerular blood flow and filtration and thus return of renal function.

The effect of angiotensin, noradrenaline and vasopressin on blood flow distribution in the rat kidney

1. The effect of val(5)-angiotensin II amide, noradrenaline and vasopressin, on kidney volume and intrarenal distribution of carbon particles and thioflavine S was examined in the rat.2. Angiotensin produced a dose-dependent shrinkage of the kidney coinciding with the rise in systemic blood pressure. Noradrenaline and vasopressin, however, produced reduction in kidney volume only in much higher doses than were necessary to produce a pressor effect.3. An intravenous infusion of angiotensin sufficient to produce a diuretic response resulted in a striking increase in glomerular content of injected carbon particles, and a marked reduction in filling of the capillary plexuses of the subcortex and outer medulla. The reduction in outer medullary filling was also observed using the thioflavine S technique.4. Noradrenaline infused in amounts sufficient to produce diuresis, aortic constriction above the kidney and vasopressin injection produced no measurable change in carbon particle distribution.5. The reduction in capillary blood flow produced by angiotensin may result in impaired tubular reabsorptive capacity by reducing peritubular removal of reabsorbate, or by reducing oxygen availability. Thus the vasoconstrictor effects of angiotensin may explain its diuretic action.

Renal tubular flow dynamics during angiotensin diuresis in the rat

1. Tubular size and lissamine green transit times were measured in rat kidneys undergoing a diuretic response to angiotensin II (0.5 mug/kg per min), and compared with the changes observed during diuresis induced by osmotic diuretics, noradrenaline and chlorothiazide.2. Angiotensin always caused a marked prolongation in proximal and distal tubular transit times; individual distal convolutions were coloured for prolonged periods, and lissamine green appeared in high concentration in distal tubules.3. Marked changes were observed in superficial tubular calibre during a stable diuretic response to angiotensin. Where distal tubular diameter was normal for the rate of urine flow, proximal tubular volume was generally reduced. In a number of experiments, however, distal tubules were markedly dilated, and in these cases proximal tubular volume was also often increased. Angiotensin may therefore be capable of causing a degree of internal hydronephrosis in the rat kidney.4. Prolongation of dye transit times, and the appearance of a concentrated lissamine green bolus in distal tubules, was suggestive of a decreased superficial nephron flow rate, indicating that the diuretic effect of angiotensin may take place only through deeper nephrons.