INFLUENCE OF SODIUM DEPRIVATION AND LOADING ON THE PLASMA-RENIN IN MAN

Oral rehydration solution normalizes plasma renin and aldosterone levels in patients with ulcerative colitis after proctocolectomy

Objectives: The possible effects and benefits of oral rehydration solution (ORS) on chronic dehydration after total proctocolectomy. Methods: To evaluate the effect of ORS on the renin-angiotensin system after remnant proctocolectomy in patients with ulcerative colitis (UC), we selected 20 patients after remnant proctocolectomy, ileal J pouch-anal anastomosis, and construction of a diverting ileostomy for UC. Patients were randomly divided into two groups, A (n=9) or B (n=11), 2 weeks after the surgery. In group A, ORS (1000 mL/day) was given for the first 7 days and mineral water (1000 mL/day) for the next 7 days. In group B, mineral water (1000 mL/day) was given for the first 7 days and ORS (1000 mL/day) for next 7 days. Plasma levels of renin, aldosterone and excretion of sodium in urine were evaluated at days 0, 7, and 14. We defined day 0 as the day of beginning this study. Results: Mean plasma renin levels on day 0 were six to eight times greater than the upper normal limit. In group A, ORS lowered plasma renin levels. In group B, plasma levels of renin and aldosterone after ORS were lower than those at days 0 and 7. Conclusions: ORS corrected increased plasma levels of renin and aldosterone to within the normal range in patients after proctocolectomy.

Chronic blood pressure control

Chronic blood pressure is maintained within very narrow limits around an average value. However, the multitude of physiologic processes that participate in blood pressure control present a bewildering array of possibilities to explain how such tight control of arterial pressure is achieved. Guyton and Coleman and colleagues addressed this challenge by creating a mathematical model that integrated the short- and long-term control systems for overall regulation of the circulation. The hub is the renal-body fluid feedback control system, which links cardiac function and vascular resistance and capacitance with fluid volume homeostasis as the foundation for chronic blood pressure control. The cornerstone of that system is renal sodium excretory capability, which is defined by the direct effect of blood pressure on urinary sodium excretion, that is, "pressure natriuresis." Steady-state blood pressure is the pressure at which pressure natriuresis balances sodium intake over time; therefore, renal sodium excretory capability is the set point for chronic blood pressure. However, this often is misinterpreted as dismissing, or minimizing, the importance of nonrenal mechanisms in chronic blood pressure control. This article explains the renal basis for the blood pressure set point by focusing on the absolute dependence of our survival on the maintenance of sodium balance. Two principal threats to sodium balance are discussed: (1) a change in sodium intake or renal excretory capability and (2) a change in blood pressure. In both instances, circulatory homeostasis is maintained because the sodium balance blood pressure set point is reached.

Parathyroid hormone-related protein stimulates plasma renin activity via its anorexic effects on sodium chloride intake

Parathyroid hormone-related protein (PTHrP) increases renin release from isolated perfused kidneys and may act as an autacoid regulator of renin secretion, but its effects on renin in vivo are unknown. In vivo, PTHrP causes hypercalcemia and anorexia, which may affect renin. We hypothesized that chronically elevated PTHrP would increase plasma renin activity (PRA) indirectly via its anorexic effects, reducing sodium chloride (NaCl) intake and causing NaCl restriction. We infused male Sprague-Dawley rats with the vehicle (control) or 125 μg PTHrP/day (PTHrP) via subcutaneous osmotic minipumps for 5 days. To replenish NaCl consumption, a third group of PTHrP-infused rats received 0.3% NaCl (PTHrP + NaCl) in their drinking water. PTHrP increased PRA from a median control value of 3.68 to 18.4 ng Ang I·ml(-1)·h(-1) (P < 0.05), whereas the median PTHrP + NaCl PRA value was normal (7.82 ng Ang I·ml(-1)·h(-1), P < 0.05 vs. PTHrP). Plasma Ca(2+) (median control: 10.2 mg/dl; PTHrP: 13.7 mg/dl; PTHrP + NaCl: 14.1 mg/dl; P < 0.05) and PTHrP (median control: 0.03 ng/ml; PTHrP: 0.12 ng/ml; PTHrP + NaCl: 0.15 ng/ml; P < 0.05) were elevated in PTHrP- and PTHrP + NaCl-treated rats. Body weights and caloric consumption were lower in PTHrP- and PTHrP + NaCl-treated rats. NaCl consumption was lower in PTHrP-treated rats (mean Na(+): 28.5 ± 4.1 mg/day; mean Cl(-): 47.8 mg/day) compared with controls (Na(+): 67.3 ± 2.7 mg/day; Cl(-): 112.8 ± 4.6 mg/day; P < 0.05). NaCl consumption was comparable with control in the PTHrP + NaCl group; 0.3% NaCl in the drinking water had no effect on PRA in normal rats. Thus, our data support the hypothesis that PTHrP increases PRA via its anorexic effects, reducing NaCl intake and causing NaCl restriction.

Endogenous ouabain and the renin-angiotensin-aldosterone system: distinct effects on Na handling and blood pressure in human hypertension

OBJECTIVE

To evaluate whether the renin-angiotensin-aldosterone system (RAAS) and endogenous ouabain system differently affect renal Na handling and blood pressure.

METHODS

Three hundred and one patients in whom we compared blood pressure, and renal Na tubular reabsorption in the basal condition and 2 h (T120) after saline infusion.

RESULTS

Following multivariate-adjusted linear and quartiles analysis, baseline mean blood pressure (MBP) was significantly higher (113.7 ± 1.33 mmHg) in the fourth versus the first endogenous ouabain quartile (103.8 ± 1.04 mmHg) and the trend across the quartiles was highly significant (β = 0.23, P = 3.53e-04). In contrast, an inverse relationship was present in the renin activity (PRA) quartiles with MBP highest in the first (112.5 ± 1.26) and lowest in the fourth PRA quartile (107.6 ± 1.48, P = 0.039). Following an acute saline load, changes in MBP and the slope of the pressure-natriuresis relationship were inversely related across the PRA quartiles. The fractional excretion of sodium (FENa) showed a negative linear trend going from the first to the third endogenous ouabain quartiles (2.35 ± 0.17 and 1.90 ± 0.14%, P = 0.05). Patients in the fourth endogenous ouabain quartile (>323 pmol/l) showed increased FENa T120 (2.78 ± 0.18%, P < 0.01) and increased Na tubular rejection fraction (P = 0.007) after Na load. After the saline load, there was a biphasic relationship between plasma endogenous ouabain and FENa favoring Na retention at low endogenous ouabain and Na excretion at high endogenous ouabain levels.

CONCLUSION

The RAAS and endogenous ouabain system are two independent and complementary systems having an inverse (RAAS) or a direct (endogenous ouabain system) relationship with hemodynamic parameters.

Effects of saline loading on the perfused cat kidney

1. Isolated cat kidneys perfused at constant pressure with blood from normal animals respond either to infusion or to injection of 0-9% NaCl (5-20 ml./150 ml. blood) by diuresis, natriuresis, a fall of the Na concentration in the urine, a fall followed by a rise in urinary Na/K and a rise in renal blood flow. The filtration fraction remains unchanged (Figs. 1, 2). 2. Kidneys perfused either with blood from intact donors at constant blood flow or with blood from hypophysectomized donors at constant pressure show no vascular response to dilution of the blood with 0 9% NaCl. Saline dilution still causes diuresis and natriuresis. The concentration of urinary Na rises, as does Na/K without an initial fall (Figs. 3, 4). 3. Kidneys perfused with blood from headless animals are unable to respond to saline loading (Fig. 6). 4. Extracts of posterior hypothalamus convert the modified response of the kidney perfused with blood from hypophysectomized animals an dilution of the blood with saline to the response given when blood from intact animals is used (Figs. 3-5). 5. Renal responses to saline loading are shown to be due to two hormones, and are dependent on the presence of an unidentified intracranial hormone, related to hypophysial hormones.

ANG II reduces net acid secretion in rat outer medullary collecting duct

In rat outer medullary collecting duct (OMCD), the mechanism(s) and regulation of H+ secretion are not understood fully. The effect of changes in acid-base balance and the renin-angiotensin system on net H+ secretion was explored. Rats received NaCl, NaHCO3, NH4Cl, or nothing in their drinking water for 7 days. Total ammonia and total CO2 (JtCO2) fluxes were measured in OMCD tubules perfused in vitro from rats in each treatment group. JtCO2 was reduced in tubules from rats drinking NH4Cl relative to those drinking NaHCO3. Because NH4Cl intake increases plasma renin and aldosterone, we asked if upregulation of the renin-angiotensin system reduces net H+ secretion. Deoxycorticosterone pivalate administered in vivo did not affect JtCO2. However, ANG II given in vivo at 0.1 ng/min reduced JtCO2 by 35%. To determine if ANG II has a direct effect on acid secretion, JtCO2 was measured with ANG II applied in vitro. ANG II (10-8 M) present in the bath solution reduced JtCO2 by 35%. This ANG II effect was not observed in the presence of the AT1 receptor blocker candesartan. In conclusion, in rat OMCD, JtCO2 is paradoxically reduced with NH4Cl ingestion. Increased circulating ANG II, as occurs during metabolic acidosis, reduces JtCO2.

Dietary salt and hypertension: a scientific issue or a matter of faith?

Many workers have an overly simplistic view of the relationship between salt intake and hypertension. This article attempts a critical evaluation of some of the evidence.

Bicarbonate transport along the loop of Henle. II. Effects of acid-base, dietary, and neurohumoral determinants

The loop of Henle contributes to renal acidification by reabsorbing about 15% of filtered bicarbonate. To study the effects on loop of Henle bicarbonate transport (JHCO3) of acid-base disturbances and of several factors known to modulate sodium transport, these in vivo microperfusion studies were carried out in rats during: (a) acute and chronic metabolic acidosis, (b) acute and chronic (hypokalemic) metabolic alkalosis, (c) a control sodium diet, (d) a high-sodium diet, (e) angiotensin II (AII) intravenous infusion, (f) simultaneously intravenous infusion of both AII and the AT1 receptor antagonist DuP 753, (g) acute ipsilateral mechanicochemical renal denervation. Acute and chronic metabolic acidosis increased JHCO3; acute metabolic alkalosis significantly reduced JHCO3, whereas chronic hypokalemic alkalosis did not alter JHCO3. Bicarbonate transport increased in animals on a high-sodium intake and following AII administration, and the latter was inhibited by the AII (AT1) receptor antagonist DuP 753; acute renal denervation lowered bicarbonate transport. These data indicate that bicarbonate reabsorption along the loop of Henle in vivo is closely linked to systemic acid-base status and to several factors known to modulate sodium transport.

Blood pressure 24-hour pattern in two industrialized countries (Italy and Japan) with a different culture in salt intake

This study investigates the blood pressure (BP) 24-hour pattern in representative samples of 2 industrialized countries, Italy and Japan, showing different cultures in salt intake. BP was monitored by means of a noninvasive ambulatory device whose readings were analyzed by means of chronobiometric procedures. The results show that the 24-hour BP pattern is not substantially different in Italian and Japanese subjects. In particular, the expected lower BP in the Italians was not detected despite their lower salt intake. Because the 24-hour mean BP value was seen not to be proportional to salt intake, the hypothesis is formulated that maintenance of the pressure regimen within a given range of variability is a principle of human physiology. To comply with this rule the Japanese people are supposed to have ethnically developed a certain resistance to dietary salt for which their cardiovascular apparatus is protected (phyletic escape to dietary sodium excess).

Atrial-specific granule number and plasma atrial natriuretic peptide in rats: effects of beta-adrenoceptor blockade and sodium intake

An interrelationship between atrial natriuretic peptide (ANP) and the renin-angiotensin system has been established. Both of these hormonal systems are modulated by sodium balance. The role of the beta-adrenoceptor in the regulation of release of ANP is not clear. We therefore undertook a study to examine changes in atrial-specific granule number and plasma ANP level following beta-adrenoceptor blockade in rats on low and high sodium intakes. A low-sodium diet, as compared with a high-sodium diet, elevated right and left atrial-specific granule number (right atria 54.6 +/- 8.7 vs. 42.3 +/- 5.7; left atria 47.7 +/- 7.7 vs. 30.6 +/- 3.4 granules/unit area) and plasma renin activity (28 +/- 3.7 vs. 5.4 +/- 0.8 ng AI/ml/hr). Plasma ANP levels were lower in the low-sodium animals (98 +/- 34 vs. 345 +/- 38 pg/ml). When treated with the nonspecific beta-adrenoceptor blocker propranolol, the elevated plasma renin activity and atrial-specific granule number in rats on a low sodium intake were significantly less. Neither of these parameters changed in rats on a high sodium intake. Conversely, propranolol treatment resulted in lower plasma ANP levels in rats with high sodium intake. The already-suppressed plasma ANP level in rats on a low-sodium diet was unaltered with beta-adrenoceptor blockade. The results suggest that dietary sodium intake is an important determinant of the response of atrial-specific granule number and plasma ANP levels following beta-adrenoceptor blockade with propranolol.

Effect of volume depletion on the afferent arterioles in the avian kidney

Nine white leghorn chickens were injected i.m. with furosemide (10 to 60 mg/kg body weight) twice daily for 18 days. The birds were then anesthetized with a combination of equithesin and diazepam and the kidneys perfused via the heart. Kidney tissue was sectioned serially and the granular epithelioid cells were counted in the juxtaglomerular apparatuses of the furosemide treated birds and in 3 normal chickens. Hyperplasia and hypergranulation of the epithelioid cells was found to occur in the juxtaglomerular apparatuses of both mammalian and reptilian type nephrons (with and without Henles loop) in the furosemide treated group. This finding was interpreted as an effect of hypovolaemia on the juxtaglomerular apparatuses. Furosemide caused an immediate stop in weight gain, an increase in the erythrocyte volume fraction and a sudden drop in blood pressure. The blood pressure later rose to subnormal levels. The heart rate was not altered. Plasma sodium and chloride fell significantly one day after furosemide administration and remained low throughout the experiment. Potassium fell during the second part of the experimental period. Captopril was injected after 18 days of furosemide treatment and lowered the blood pressure significantly. This was interpreted as indirect evidence for the presence of renin in the granular epithelioid cells and indicates the importance of the renin angiotensin system in maintaining the blood pressure in hypovolaemic conditions.

Relationship between plasma renin activity and physical fitness in normal subjects

The relationship between plasma renin activity (PRA) at rest and physical fitness was studied in 40 normal young subjects on a liberal sodium intake. Plasma renin activity was measured in arterial blood withdrawn at the end of a 30-min period of rest in recumbency, while physical fitness was expressed by the highest oxygen uptake achieved during an uninterrupted graded exercise test performed in the sitting position on an electromagnetically braked ergometer bicycle (peak VO2). Log PRA correlated significantly and inversely with peak VO2 adjusted for body weight (r = -0.34; P less than 0.05) in single regression analysis. Using multiple regression and adjusted peak VO2, age, urinary sodium excretion and mean intra-arterial pressure as independent variables, no combination of two or more independent variables yielded significant partial correlation coefficients with log PRA. This correlation suggests that PRA at rest is inversely related to the subject's physical fitness.

Effect of oral glucose loading on plasma insulin, potassium, renin and aldosterone in normal subjects and patients with primary hyperaldosteronism

The effects of standard oral glucose loading (100 g) on plasma aldosterone and some regulatory factors were assessed in patients with primary hyperaldosteronism and normal subjects. Following overnight fast, mean plasma glucose was identical (10 patients and normal subjects approximately matched per age and sex); plasma insulin, potassium and renin levels were lower and plasma aldosterone higher in the patients. Glucose loading significantly increased plasma glucose and insulin concentrations and decreased plasma potassium and aldosterone levels in both groups; plasma renin activity was significantly increased only in normal subjects. The increases in plasma insulin and the decreases in plasma potassium or aldosterone tended to be blunted in primary hyperaldosteronism. Relationships among glucose-induced changes in plasma aldosterone and other factors were assessed by multiple regression analysis in these patients and normal subjects as well as an additional group of 21 normal subjects; in the latter, plasma cortisol was also measured and found to decrease significantly after glucose loading. Changes in plasma aldosterone correlated (P less than 0.025) more closely with those in plasma potassium in the patients and with variations in plasma renin activity in the normal subjects. These findings suggest that complex metabolic changes occur following glucose ingestion which are capable of modifying aldosterone secretion in normal subjects and primary hyperaldosteronism. The aldosterone-inhibitory effect of glucose tends to be blunted in the latter disorder. This could be related at least in part to an impaired insulin response in primary hyperaldosteronism.

Sodium, potassium and age: possible determinants of plasma renin activity and aldosterone during childhood (age 4-16)

The renin-angiotensin-aldosterone system was studied in fifty healthy children aged 4-16 years under normal sodium and potassium intake. The plasma renin activity (PRA) and plasma aldosterone (PA) decreased with age: r = -0.30, P less than 0.05 for plasma renin activity and r = -0.33, P less than 0.05 for plasma aldosterone. Significant negative correlation was obtained between plasma renin activity and the 24-h urinary sodium excretion; r = -0.40, P less than 0.01. This relationship remained significant when the daily urinary sodium excretion was corrected for 1.73 m2 body surface area (BSA); r = -0.40, P less than 0.01. Using the multivariance analysis, plotting the plasma renin activity against the two combined parameters (24-h urinary sodium excretion and age), no improvement was obtained (r = 0.38, P greater than 0.05). This finding suggests that during childhood, sodium rather than age has a major modulatory role on plasma renin activity. With advancing age the plasma aldosterone showed a significant positive correlation coefficient with plasma renin activity(r = 0.29, P less than 0.05). Multivariance analysis between plasma aldosterone and the two combined parameters, Plasma renin activity and age, significantly improved the correlation coefficient (r = 0.42, P less than 0.05) suggesting that both plasma renin activity and age play a dominant modulatory role in the control of plasma aldosterone during childhood. Neither 24-h urinary sodium excretion, nor 24-h urinary potassium excretion, improved the multiple correlation coefficient with plasma aldosterone when added to plasma renin activity and age.

Inborn error in the terminal step of aldosterone biosynthesis. Corticosterone methyl oxidase tpe II deficiency in a North American pedigree

Profound salt wasting developed in a male infant who had marked reductions in serum and urinary aldosterone concentrations despite striking hyperreninemia. Coincident elevations in plasma and urinary levels of specific 18-hydroxysteroids localized the defect to corticosterone methyl oxidase Type II, the adrenal enzyme responsible for the final step of aldosterone synthesis. Salt replacement but not hydrocortisone ameliorated the clinical and metabolic abnormalities. Evaluation of 33 other family members disclosed the biochemical disorder in six other subjects who were affected in an autosomal-recessive pattern with variably severe clinical manifestations and abnormal ratios of 18-hydroxycorticosterone (or its metabolites) to aldosterone. This inborn error in aldosterone biosynthesis must be distinguished from other heritable, salt-losing defects in adrenal steroidogenesis.

Angiotensin II and renal hypertension in dog, rat and man: effect of converting enzyme inhibition

The role of the renin-angiotensin system in the pathogenesis of one-clip, two-kidney hypertension has been studied in man, dog and rat. Particular attention has been paid to peripheral plasma concentrations of angiotensin II in different circumstances; angiotensin II infusion has been combined with radioimmunoassay to construct angiotensin II/blood pressure dose-response curves. The effect of converting enzyme inhibitors has been studied, precautions being taken to avoid obtaining falsely high values for plasma angiotensin II because of cross-reaction with angiotensin I in these circumstances. The initial phase of one-clip, two-kidney hypertension is attributable to the direct pressor effect of the immediate rise in plasma angiotensin II. Subsequently, plasma angiotensin II is relatively lower, although blood pressure remains high. This upward resetting of the plasma angiotensin II/blood pressure relationship can be mimicked by infusing angiotensin II chronically at low dose. After reconstruction of a stenosed renal artery, or excision of a post-stenotic kidney, the angiotensin II/blood pressure relationship returns slowly to normal. In this second phase of one-clip, two-kidney hypertension, the long-term administration of saralasin, or of converting enzyme inhibitor, can also return arterial pressure to normal; brief administration of these drugs is less effective or ineffective. The results are compatible with, although they do not conclusively establish, an important slow pressor action of the renin-angiotensin system in the second phase of one-clip, two-kidney hypertension. This provides a rational basis for the use of captopril clinically in this condition.

Responses of plasma renin activity and dopamine-beta-hydroxylase to increased intravascular volume

Circadian variations of plasma renin activity, plasma dopamine-beta-hydroxylase, and urinary aldosterone excretion were measured in man under conditions of high- and low-sodium intake. Plasma renin activity and urinary aldosterone excretion were maximal at 8 a.m. Plasma DBH shows small, biologically insignificant circadian fluctuations. In three subjects on low-salt diets, the values were lower than those in the same subjects on high-salt diets. Expansion of intravascular volume in supine normal volunteers lowered plasma renin and DBH activity, and also resulted in a significant natriuresis. The decline in DBH activity probably reflects a decrease in its release from autonomic nerve endings and thus demonstrates in man an effect of decreasing autonomic activity.

Renal function and renin secretion after administration of ouabain and ouabain plus furosemide in conscious sheep

The effects of ouabain or ouabain and furosemide on renal function and renin secretion were studied in conscious isovolemic sheep. The sheep received a continuous renal arterial infusion of papaverine, 7 mg/min, throughout the experiment. Ouabain alone (7 X 10(-7) M in the renal plasma) produced significant decreases in glomerular filtration rate (GFR) and renal plasma flow (RPF) but not in renal perfusion pressure. Plasma [K+] rose after ouabain administration. Fractional (FENa) and absolute (UNaV) Na+ excretion were 2.9 +/- 1.0% (mean +/- SE) and 78 +/- 54 muEq/min, respectively, during the papaverine infusion and rose to 19 +/- 5.1% (P less than 0.05) and 528 +/- 116 muEq/min (P less than 0.01) after ouabain administration. Despite the large changes in Na+ reabsorption, renin secretion was not stimulated. During the control period, renin secretion was 281 +/- 131 ng/min and the average renin secretion after ouabain administration was 310 +/- 78 ng/min (not significant). A smaller dose of ouabain (2 X 10(-7) M) infused into the renal artery with 40 mg of furosemide, iv, did not decrease GFR but RPF was suppressed. FENa and UNaV averaged 4.4 +/- 1.6% and 121 +/- 44 muEq/min, respectively, while papaverine was infused into the renal artery and increased to 18 +/- 4.8% (P less than 0.05) and 636 +/- 209 muEq/min (P less than 0.05) after ouabain and furosemide were infused. Renin secretion was 118 +/- 62 ng/min during the control period and averaged 240 +/- 67 ng/min after ouabain plus furosemide. The difference was not statistically significant. Thus ouabain alone does not stimulate renin secretion in the conscious, isovolemic sheep despite a presumed increase in [NaCl] at the macula densa and inhibition of NaCl transport by the loop of Henle. Ouabain also blocks the normal stimulatory effects of furosemide on renin secretion.

The relationship between body fluid volume, sodium ion concentration, and sensitivity to pressor effect of angiotensin II in dogs

Extracellular fluid volume, plasma electrolyes, and plasma angiotensin II (A II) were individually controlled to determine their influence on the acute pressor responsiveness to A II. Hemodialysis of nephrectomized dogs was used to simulate and control the changes of major variables which occur in the intact state during changes in sodium balance. A II dose-pressure response curves were determined in 11 dogs at three volume states with plasma [Na+] maintained constant and in five dogs at low, normal, and high plasma [Na+] with body fluid volume maintained constant. Parallel shifts of the log dose-response curves were obtained in the three volume states. The same rise in arterial pressure with identical doses of A II was obtained at normal, contracted, and expanded volume states, with the change of arterial pressure based on the uncompensated basal pressure level at each volume state. When the fall in pressure observed during volume depletion was returned to control levels with norepinephrine, there was no change in the A II dose-response relationship from the control state. No difference in the A II dose-pressure response relationship was obtained between states of 140, 146, and 156 mEq/liter plasma [Na+] with body fluid volume held constant. The studies indicate that short-term alterations in either sodium or water balance do not alter the "real" vascular sensitivity to A II. The "apparent" changes normally observed result from preexisting endogenous levels of circulating A II present at the time the dose-response curve is determined which probably alter the availability of receptor sites to A II.

Plasma aldosterone during extracellular fluid volume expansion in patients on regular haemodialysis

The influence of extracellular fluid volume expansion on the plasma aldosterone concentration (PAC) was investigated in five anephric and six non-nephrectomized patients on regular haemodialysis, and compared to a control group of four anephric and four non-nephrectomized patients. Plasma-renin activity, cortisol, Na+, and K+ were measured together with the PAC during the investigation. In anephric patients the PAC remained constant during the control period as well as during extracellular fluid volume expansion by infusion of 350 mmol of 20% mannitol. In the non-nephrectomized patients PAC diminished after mannitol infusion. The decline in PAC was correlated with the basal levels of PAC and the plasma renin activity. It is concluded that 5% extracellular fluid volume expansion has no direct influence on the regulation of PAC in patients without the renal renin-angiotensin system and that the regulation of PAC in anephric patients in the present investigation is probably mediated by changes in potassium and ACTH.

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.

Impaired renal conservation of sodium and chloride during sustained correction of systemic acidosis in patients with type 1, classic renal tubular acidosis

In 10 patients with classic renal tubular acidosis in whom correction of acidosis was sustained with orally administered potassium bicarbonate, renal conservation of sodium was evaluated when dietary intake of sodium was restricted to 9--13 meq/day. In five patients, renal conservation of sodium was impaired by at least one criterion of impairment. In the remaining patients, renal conservation of sodium appeared to be relatively well-maintained, but an impairment could not be excluded. In each of six patients studied during induced water diuresis, including two in whom renal conservation of sodium was not unequivocally impaired, the minimal urinary concentrations of sodium were inappropriately high and the urinary excretion rates of sodium were flow-dependent. These results provide direct evidence that an abnormality in renal transport of sodium can occur in classic renal tubular acidosis, and compel a reconsideration of the pathophysiology of disordered renal transport of sodium in this disorder. The results indicate that in at least some patients with classic renal tubular acidosis impaired renal conservation of sodium is not exclusively a reversible consequence of the renal acidification defect. These findings raise the question whether renal transport of sodium is unimpaired in any patients with classic renal tubular acidosis. In the presently studied patients, the impairment in renal conservation of sodium appeared to be in part the consequence of an impaired ability of the vasopressin-responsive segments of the distal nephron to generate and maintain appropriately steep transepithelial sodium concentration gradients.

Response of aldosterone and blood pressure to angiotensin II infusion in anephric man. Effect of sodium deprivation

Angiotensin II, infused intravenously, increased plasma aldosterone concentration in two of six anephric subjects taking their usual dietary quantities of sodium. After 3 days of dietary sodium restriction and weight-reducing hemodialysis, the aldosterone response to infused angiotensin II in the two previously reactive subjects was enhanced, while the four previously unreactive subjects also showed a rise in plasma aldosterone. Before and after sodium depletion the anephric subjects were less responsive than normal subjects. Even when sodium-depleted, the anephrics showed no further rise in plasma aldosterone when arterial plasma angiotensin II was increased by infusion to concentrations greater than 50-199pg/ml, in contrast to sodium-depleted normals who show progressive aldosterone responses with plasma angiotensin II concentrations up to at least 370pg/ml. Before the infusion of angiotensin II, arterial plasma renin, angiotensin II, and aldosterone were detectable in the anephrics, but were unchanged by dietary sodium restriction or weight-reducting hemodialysis. Sodium depletion caused significant falls in weight, plasma sodium, and blood pressure, but no changes in plasma potassium or cortisol. Increases in blood pressure in relation to increments of arterial plasma angiotensin II were unaffected by sodium depletion, as might be expected in the absence of a rise in endogenous angiotensin II.

Sensitivity of renin secretion to volume depletion in the anaesthetized dog: comparison between urinary drainage and slow haemorrhage

1. An experimental technique utilizing 'denervation diuresis' from one kidney with measurement of renin release from the contralateral innervated kidney was developed to study the sensitivity of renin secretion to volume depletion. 2. With urine excretion, release of renin increased progressively from the innervated kidney. The increase was significant at a sodium deficit of 0-23 mole.kg-1. At a sodium deficit of 0-6 m-mole.kg-1 renin release had doubled. 3. Bilateral vagotomy did not alter this response. 4. Precise replacement of sodium loss with isotonic saline but without replacement of other urinary components returned renin release to control levels. 5. Slow haemorrhage causing a rate of volume and sodium loss equivalent to urinary drainage did not alter the rate of renin release. 6. With a single denervated kidney and contralateral nephrectomy, renin release fell progressively to minimal levels despite sodium deficits up to 2-6 m-mole.kg-1. 7. It is concluded that renin secretion is sensitive to at most a 0-5% change in body fluid volume and should be considered a primary response to volume depletion. The sensitivity of the response depends upon normal renal innervation but is not mediated via vascular volume receptors nor via receptors innervated by the vagus. 8. It is proposed that the extreme sensitivity of the renin-secreting system in these experiments results from the combination of volume depletion and slight hypotonicity of extracellular fluid acting on the renal afferent arteriole without the mediation of the macula densa,

Effect of renin-angiotensin system on sodium intake

1. Water and saline intake was measured in rats depleted of Na by I.P. dialysis. Na intake was prevented 180 min but not 60-90 min after bilateral nephrectomy. Unilateral nephrectomy as well as ureteral ligature had no effect on Na intake. 2. Renin (3u.) injected I.P. re-established the Na appetite abolished by nephrectomy. 3. Angiotensin I (5 ng) or II (5-40 ng) injected into the 3rd ventricle, also restored the Na intake and this effect was dose-dependent. 4. The angiotensin converting-enzyme inhibitor Sq 20,881 (1 mg/kg) inhibited the effect of AI but not that of AII in restoring Na intake. 5. It is concluded that the kidneys might play a role in the regulation of Na intake through the renin-angiotensin system.

Renin secretion at the individual nephron level

Blood was collected from the descending aorta, from a renal efferent arteriole and from the renal vein of a rat. The renin concentrations of the blood samples were measured. The renal vein renin concentration was 673 +/- 81 (SE) ng ml-1h-1 which was significantly higher than the concentration in the aorta of 456 +/- 50 (SE) ng ml-1h-1. The concentration of renin in the renal efferent arteriole was significantly lower than that in the aorta. These observations imply that net renin secretion is a combination of two processes; removal between artery and efferent arteriole and entry between efferent arteriole and renal vein. It appears that renin is released into the interstitium and enters the circulation at the capillary level rather than being released into the afferent or efferent arterioles. This mode of secretion supports the suggestion that the renin angiotensin system may primarily work intra-renally rather than through the systemic circulation.

Prior receptor occupancy as a determinant of the pressor activity of infused angiotensin II in the rat

The pressor responsiveness to angiotensin II and norepinephrine was examined in rats before and during blockade of coverting enzyme activity with the nonapeptide SQ 20881. Responses to angiotensin II were impaired by sodium deprivation but enhanced by sodium loading or bilateral nephrectomy. During the period of converting enzyme blockade, a twofold increase in the angiotensin II pressor response was observed in the salt-restricted rats, whereas only a small change occurred in the salt-loaded rats. Infusion of the inhibitor produced a profound fall in the blood pressure of the salt-depleted rats with a relatively minor fall in the sodium-loaded rats. Norepinephrine pressor responses were slightly potentiated in the salt-restricted rats after administration of SQ 20881, but no change occurred in the salt-loaded or the nephrectomized rats. These observations support the view that the decreased angiotensin II pressor activity during salt deprivation is the result of a prior occupancy of receptor sites by endogenous hormone. Therefore, a change in the number or the affinity of receptors consequent to changes in sodium balance need not be postulated to explain the phenomenon.

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

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

Sensitization of the Adrenal Cortex to Angiotensin II in Sodium-Deplete Man

The effect of sodium depletion on the dose-response relationships of angiotensin II to aldosterone and blood pressure was studied. Arterial plasma angiotensin II and aldosterone and arterial blood pressure were measured before and during the incremental infusion of angiotensin II into sodium-replete and sodium-deplete subjects. Sodium depletion caused a distinct steepening of the angiotensin Il-aldosterone dose-response curves in four of five subjects and a concurrent diminution in the pressor effect of angiotensin II. Administration of angiotensin II did not demonstrably alter the half-life of aldosterone. Sodium depletion did not change the plasma concentrations of sodium or potassium, but it was accompanied by a significant increase in plasma levels of 11-hydroxycorticosteroids and magnesium. The contrasting effects of sodium depletion on the aldosterone and the pressor dose-response curves favored sodium retention. These results are consistent with an important role for the renin-angiotensin system in the control of aldosterone secretion in man.

Mechanism of the redistribution of renal cortical blood flow during hemorrhagic hypotension in the dog

Studies were performed to define the mechanisms involved in the redistribution of renal cortical blood flow to inner cortical nephrons which occurs during hemorrhagic hypotension in the dog. The radioactive microsphere method was utilized to measure regional blood flow in the renal cortex. Renal nerve stimulation decreased renal blood flow 40% but had no effect on the fractional distribution of cortical blood flow. Pretreatment with phenoxybenzamine, phentolamine, propranolol, or atropine did not alter the redistribution of cortical flow during hemorrhage. A reduction in renal perfusion pressure by aortic constriction caused a qualitatively similar alteration in regional blood flow distribution as occurred during hemorrhage. When perfusion pressure was kept constant in one kidney by aortic constriction followed by hemorrhage, no redistribution occurred in the kidney with a constant perfusion pressure while the contralateral kidney with the normal perfusion pressure before hemorrhage had a marked increase in the fractional distribution of cortical flow to inner cortical nephrons. Additionally, retransfusion had no effect on the fractional distribution of flow in the kidney in which perfusion pressure was maintained at the same level as during hemorrhage while in the contralateral kidney in which pressure increased to normal there was a redistribution of flow to outer cortical nephrons. These studies indicate that the redistribution of renal cortical blood flow which occurs during hemorrhage is not related to changes in adrenergic activity but rather to the intrarenal alterations which attend a diminution in perfusion pressure.

Plasma renin activity and blood pressure in 89 patients receiving maintenance haemodialysis therapy

Blood pressure, plasma renin activity, plasma sodium concentration, plasma potassium concentration, dietary sodium intake, and duration of dialysis have been measured under standard conditions in 89 patients on maintenance haemodialysis. No significant relation was found between plasma renin activity and blood pressure. Statistically significant correlations were found between plasma renin activity and plasma sodium concentration and between plasma renin activity and dietary sodium intake.Only one patient was found to have uncontrollable hypertension associated with a markedly raised plasma renin activity. Reasons are given for not performing bilateral nephrectomy in this patient. We believe the low incidence of uncontrollable hypertension and hyperreninaemia in our patients to be due to their slow introduction to haemodialysis, thus preventing violent swings in body weight, blood pressure, and renin secretion.Although plasma renin activity did fall with duration of dialysis, all 15 patients who have been on maintenance dialysis for longer than five years have normal levels.

Effects of renal arterial infusion of sodium and potassium on renin secretion in the dog

The nonfiltering kidney model was used to determine whether sodium or potassium inhibits renin secretion in the absence of a functional macula densa in dogs with thoracic inferior vena caval constriction. The control rate of renin secretion was high, and decreases were readily recognized. After control observations, hypertonic sodium chloride or hypertonic potassium chloride was infused into the renal artery for 1 hour, and renin secretion was measured at 15-minute intervals. An increase in renal venous plasma sodium concentration from 141 to 154-158 mEq/liter caused no change in renin secretion for the first 45 minutes of infusion in dogs with a nonfiltering kidney. In contrast, dogs with thoracic caval constriction but with a filtering kidney showed a striking decrease in renin secretion during intrarenal sodium infusion (3,097 to 1,061 ng angiotensin/min, P <0.02). An increase in renal venous plasma potassium concentration from 3.9 to 6.1 mEq/liter in one group of dogs and from 4.9 to 8.3 mEq/liter in a second group also caused no change in renin secretion in the nonfiltering kidney of dogs with thoracic caval constriction. However, in dogs with thoracic caval constriction and a filtering kidney, potassium infusion decreased renin secretion (1,952 to 984 ng angiotensin/min, P <0.05). In all experiments, infusion of sodium chloride or potassium chloride failed to produce a significant change in renal blood flow, arterial blood pressure, or inferior vena caval pressure. Therefore, no evidence was obtained for a vascular action or a direct effect of sodium or potassium on the juxtaglomerular cells, and the data are consistent with an action mediated by the renal tubular system.

Comparison of surgery and prolonged spironolactone therapy in patients with hypertension, aldosterone excess, and low plasma renin

The effect of prolonged preoperative treatment with spironolactone has been studied in a series of 67 patients with hypertension, aldosterone excess, and low plasma renin. In the series as a whole a highly significant reduction in both systolic and diastolic pressures was achieved, with no evidence of escape from control during therapy lasting several years in some cases. The drug was equally effective in controlling blood pressure in patients with and without adrenocortical adenomata. Occasional unresponsive patients were encountered in both groups; pretreatment blood urea levels in these were significantly higher than in the responsive patients. The hypotensive effect of spironolactone usually predicted the subsequent response to adrenal surgery.Spironolactone in all cases corrected plasma electrolyte abnormalities; significant increases in total exchangeable (or total body) potassium and significant reductions in total exchangeable sodium, total body water, extracellular fluid, and plasma volumes were seen. Plasma urea rose during treatment and there was a slight fall in mean body weight. Significant increases in peripheral venous plasma renin and angiotensin II concentrations occurred during treatment.In two patients no increase in aldosterone secretion rate was found during treatment, although plasma aldosterone rose in three of four subjects studied.Severe side effects were rare; in only two of the 67 patients did the drug have to be stopped.In addition to its routine preoperative use, spironolactone can now be advised as long-term therapy in selected patients.