Direct action of rat urinary kallikrein on rat kidney to release renin

To study the effect of kallikrein on renal renin release, we superfused rat renal cortical slices with 3.5 to 140 milliesterase units (mEU)/ml of purified rat urinary kallikrein. Kallikrein was a potent stimulus of renin release. Renin rose in a dose-dependent fashion from 70 mEU/ml to 140 mEU/ml. The response to 140 mEU/ml was greater than that seen with maximal doses of prostaglandin E2 (170 +/- 43%, P < 0.05) and at least the same as isoproterenol (242 +/- 49% increase), or dibutyryl cyclic AMP (272 +/- 40%). Trypsin was ineffective under these experimental conditions. Kallikrein-stimulated renin release was completely abolished by trasylol, whereas bradykinin did not increase renin production, indicating that kallikrein's effect is not mediated via kinin generation. There was no demonstrable acid activation or kallikrein activation of the superfusate and chromatography on Sephacryl S-200 revealed a single renin peak of -40,000 mol wt, suggesting that all of the renin release was in the active form. The data suggests that urinary kallikrein acts directly on the rat kidney to release renin, possibly via proteolytic conversion of prorenin to active renin. Our results support the concept that kallikrein may be an endogenous activator of prorenin in the kidney.

Urinary prostaglandin E2 excretion in chronic renal disease

To ascertain whether renal prostaglandin E2 production is impaired in chronic renal disease we measured urinary prostaglandin E2 in 25 female renal patiens, and in 38 female noirmal volunteers. Prostaglandin E2 averaged 337 +/- 63 ng/24 hr in 25 female renal patients, which was significantly higher (P < 0.01) than values in normal female subjects (166 +/- 17 ng/24 hr). None of the renal patients excreted less than 50 ng/24 hr, whereas normals when treated with indomethacin averaged 30 +/- 10 ng/24 hr (n=8). There were no significant correlations between prostaglandin E2 and creatinine clearance, or urine volume. No difference in prostaglandin E2 was encountered between hypertensive and normotensive renal patients. Our results indicate that renal prostaglandin E2 production is increased rather than decreased in renal disease. The failure to demonstrate decreased urinary prostaglandin E2 excretion in renal hypertension sharply contrasts with the situation in essential hypertension.

Prostaglandin stimulation of renin release: independence of beta-adrenergic receptor activity and possible mechanism of action

Using a continuous superfusion system of rat kidney cortical slices, we investigated the renin-releasing effect of prostaglandin E2 (PGE2) and its possible mechanism of action. PGE2 caused significant stimulation of renin release in a dose-dependent fashion at concentrations of 3 x 10(-6) to 10(-4) M. Isoproterenol (8 x 10(-7) M) stimulated renin release significantly, and its effect was completely abolished by propranolol (2 x 10(-5) M). PGE2-stimulated renin release was not blocked by the same dose of propranolol. Dibutyryl cAMP caused a dose-dependent increase in renin release at concentrations of 10(-5) to 5 x 10(-3) M. Theophylline (4 x 10(-3) M) had no effect on renin release, but when added to subthreshold doses of PGE2 (10(-6) M), it stimulated renin release significantly. The simultaneous addition of maximal stimulating doses of PGE2 and dibutyryl cAMP had no additive or synergistic effects. These experiments show that PGE2 causes stimulation of renin release by a direct effect on the JG cell. The renin-releasing effect of PGE2 does not depend upon the beta-adrenergic receptors but may be mediated through cAMP.

Effects of prostaglandins on adrenal steroidogenesis in the rat

To elucidate the role of prostaglandins in adrenal steroidogenesis, we studied aldosterone and corticosterone responses to 3 x 10(-8) M--3 x 10(-4) M of prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha), prostacyclin (PGI2), and arachidonic acid (AA) in collagenase dispersed rat adrenal capsular and decapsular cells. Whereas adrenocorticotrophic hormone (ACTH) and angiotensin II (AII) stimulated aldosterone production in capsular cells and ACTH stimulated corticosterone production in decapsular cells in a dose dependent fashion, aldosterone and corticosterone production were not stimulated significantly by PGE2, PGF2 alpha, PGI2, and AA. Although preincubation of dispersed adrenal cells with indomethacin (3 x 10(-5) M) markedly inhibited PGE2 synthesis, ACTH- and AII-stimulated aldosterone production and ACTH-stimulated corticosterone production were not attenuated despite prostaglandin blockade. These results indicate that prostaglandins are unlikely to play an important role in adrenal steroidogenesis.

Sodium intake as a determinant of urinary prostaglandin E2 excretion

The effect of salt-loading on urinary prostaglandin D2 (PGE2) was studied in the rat. PGE2 doubled after 4 days of gavage with 40 ml 0.9% saline. Control animals receiving 5% glucose or tap water did not show this increase. When rats were allowed ad lib saline, PGE2 increased after 2 weeks, but returned to normal at 5 weeks. This same phenomenon of increased PGE2 early in the course of salt-loading was also observed in Dahl salt-sensitive and salt-resistant rats fed an 8% salt diet. Inhibition of prostaglandin biosynthesis by meclofenamate or indomethacin did not attenuate the natriuretic effect of saline loading. We conclude: 1) Salt-related changes in PGE2 is a time-dependent phenomenon, and 2) PGE2 is not the natriuretic factor since levels normalize despite continued salt-loading, and natriuresis was unaffected by prostaglandin blockade.

Low renin essential hypertension: failure to demonstrate excess 11-deoxycorticosterone production

11-Deoxycorticosterone (DOC) was determined by specific RIA in 27 normal subjects and in 25 normal renin and 23 low renin hypertensives. None of the patients exhibited unprovoked hypokalemia. Strict criteria were employed for renin profiling the hypertensive patients, including age matching, exclusion of diabetics, and the use of medications known to interfere with the renin response or with DOC measurements. In all 3 groups, comparable DOC levels were found in plasma and urine. In contrast, DOC was elevated in 7 of 19 patients with primary aldosteronism. These results do not support a DOC excess hypothesis for the syndrome of low renin essential hypertension.

Reversible acute renal failure induced by indomethacin

Acute renal failure occurred during indomethacin therapy in a patient with chronic pyelonephritis. Urinary prostaglandin E2 levels were diminished but returned to normal after discontinuation of drug therapy and recovery of renal function. Prostaglandins may be critical for the integrity of renal function, and the use of prostaglandin inhibitors such as indomethacin and other nonsteroidal anti-inflammatory drugs may be deleterious in patients with underlying renal disease.

Indomethacin-induced prostaglandin inhibition with hyperkalemia. A reversible cause of hyporeninemic hypoaldosteronism

Hyporeninemic hypoaldosteronism was diagnosed in a young woman with glomerulonephritis who was receiving indomethacin therapy. Despite only mildly abnormal renal function, serum K+ was elevated to 6.2 meq/L, and plasma renin activity (0.12 ng/mL h) and aldosterone (4.4 ng/dL) failed to respond to the combined stimuli of furosemide and posture. Urinary prostaglandin E2 (PGE2) was suppressed (70 ng/24 h). When indomethacin was withdrawn, significant kaliuresis occurred, accompanied by normalization of serum K+ and PGE2 and a supranormal rebound in renin and aldosterone levels. Challenge with indomethacin resulted in antikaliuresis and resuppression of PGE2, renin, and aldosterone. This case study documents for the first time that indomethacin can cause the syndrome of hyporeninemic hypoaldosteronism, probably by inhibiting prostaglandin biosynthesis.

Influence of angiotensins (I, II, & III), bradykinin and arachidonic acid on renomedullary PGE production in vitro

Renomedullary tissue from rabbit or rat was incubated with angiotensin I, II, III, arachidonic acid, bradykinin, indomethacin and meclofenamate to study their effect on PGE2 production. Arachidonic acid and bradykinin enhanced PGE2 production significantly. Indomethacin and meclofenamate inhibited PGE2 production by more than 70%. Angiotensin I, II and III did not influence PGE2 production. These results suggest that bradykinin and arachidonic acid stimulate PGE2 production by a direct cellular action whereas the angiotensins do not.

Direct non-chromatographic radioimmunoassay of aldosterone: validation of a commercially available kit and observations on age-related changes in concentrations in plasma

Human plasma aldosterone can be rapidly, directly, and reliably measured by radioimmunoassay with use of a commercially available anti-aldosterone antibody. With this method, we show that values tend to decrease with advancing age, especially after the sixth decade.

Direct non-chromatographic radioimmunoassay of aldosterone: validation of a commercially available kit and observations on age-related changes in concentrations in plasma

Human plasma aldosterone can be rapidly, directly, and reliably measured by radioimmunoassay with use of a commercially available anti-aldosterone antibody. With this method, we show that values tend to decrease with advancing age, especially after the sixth decade.

Deoxycorticosterone and 17-ketosteroids. Elevated levels in adult hypertensive patients

Plasma 11-deoxycorticosterone levels were manyfold elevated in three adult patients with hypertension and elevated urinary excretion levels of 17-ketosteroids but without Cushing's syndrome. Dexamethasone therapy resulted in suppression of these steroids and in improvement of blood pressure in two of the patients. A partial adrenal 11beta-hydroxylase deficiency appears to best explain these findings.

Impaired renal prostaglandin E2 biosynthesis in human hypertensive states

Urinary Prostaglandin E2 (PGE2), a known indicator of renal production, was measured by specific radioimmunoassay in 111 normal volunteers, 85 patients with essential hypertension, 6 with renovascular hypertension, and 23 patients with primary aldosteronism. Women excreted less PGE2 than men in both normotensive and hypertensive groups. When compared to normals, essential hypertensives demonstrated significantly lower PGE2 levels, with one third excreting less than 100 ng/24 hr, values usually seen only in subjects receiving the prostaglandin synthetase inhibitor, indomethacin. Normal PGE2 was seen in patients with renovascular hypertension, and levels were uninfluenced by treatment with the converting enzyme inhibitor SQ14225, Despite normalization of blood pressure and increased plasma renin activity. Normal PGE2 was also encountered in primary aldosteronism. These data indicate that impaired renal PGE2 biosynthesis is specific for human essential hypertension, and is not secondary to the elevated blood pressure. Although PGE2 excretion tends to be lower in low-renin hypertension, a constant relationship between PGE2 and renin is not always apparent.

Regulation of 18-hydroxydeoxycorticosterone in the rat

Simultaneous measurements of plasma 18-hydroxydeoxycorticosterone (18 OH-DOC), corticosterone, and aldosterone were performed in the rat by using RIA. Under basal conditions, 18 OH-DOC levels averaged 11.3 +/- 3.7 (SE) ng/ml. Plasma concentrations were increased 8-fold (86.8 +/- 8.0 ng/ml) 1 h after 1 U sc ACTH. Dexamethasone suppressed 18 OH-DOC to less than 1.5 ng/ml, irrespective of Na+ intake. Neither Na+ depletion nor Na+ loading had any influence on 18 OH-DOC levels. Excellent correlation between 18 OH-DOC and corticosterone (r = 0.90, P less than 0.001) was observed, whereas there was none between 18 OH-DOC and aldosterone (r = 0.061, P greater than 0.6). In the rat, 18 OH-DOC is an ACTH-dependent steroid which does not appear to be under the influence of the renin-angiotensin system.

Is low-renin hypertension an overdiagnosed syndrome?

The controversy surrounding low-renin hypertension ranges from the concept that it carries a favorable prognosis to the therory that it a form of nephrosclerosis. At least a part of the debate may result from the use of different methods of classifying patients with this condition. The study presented here clearly shows that age and sex have an important influence on plasma renin activity. Women had lower values than age-matched men, and studies in normal volunteers showed that plasma renin activity decreases with age. Other factors also affect renin profiling. Diabetes is associated with renin suppression, and blacks have lower values of plasma renin activity than whites. In addition, use of anti-inflammatory drugs such as aspirin significantly lowers renin levels. Since some of these variables have not been considered in published studies to date, it would seem that the true incidence of low-renin hypertension among hypertensives is lower than the accepted figure of 25%.

Plasma mineralocorticoids, plasma renin, and urinary kallikrein in salt-sensitive and salt-resistant rats

Plasma aldosterone, deoxycorticosterone (DOC), 18-hydroxy-deoxycorticosterone (18OH-DOC), and corticosterone were measured in Dahl salt-sensitive (S) and salt-resistant (R) rats. Plasma corticosterone and DOC were not different between strains but plasma aldosterone was decreased and plasma 18OH-DOC increased in S compared to R. Plasma renin activity and urinary kallikrein excretion were both lower in S than R. Urinary kallikrein is known to vary directly with mineralocorticoid activity and 18OH-DOC is a weak mineralocorticoid. The lower urinary kallikrein in the presence of elevated 18OH-DOC could mean that urinary kallikrein differences between S and R are under independent genetic control from 18OH-DOC.

Impaired renal production of prostaglandin E2: a newly identified lesion in human essential hypertension

To test the hypothesis that impaired renal prostaglandin production may accompany the hypertensive state, we have measured urinary PGE2 by radioimmunoassay in 52 normotensive and 50 hypertensive subjects. PGE2 levels were lower in females, and were not affected by Na+ intake or age. Patients with essential hypertension had significantly lower PGE2, particularly those with low-renin hypertension. Forty percent of the hypertensives excreted less than 70 ng/24 hr, values never observed in normotensives except after receiving indomethacin, a well-known prostaglandin synthetase inhibitor. It appears that impaired renal prostaglandin production is commonly encountered in patients with essential hypertension, perhaps contributing to their increased renal resistance. The data further suggest a role for renal prostaglandins in the pathogenesis of low-renin hypertension.

Age and the renin-aldosterone system

Age effect on plasma renin activity (PRA) and PRA classification was studied in young and older normotensive volunteers. Ambulatory PRA was lower in the older age group than in the younger with both on an unrestricted diet and a low-sodium diet. Renal function, aldosterone excretion, and plasma renin substrate were comparable in both groups. Age had a substantial effect on PRA classification. When the young normotensives were controls, 32% (6/19) older normotensives had abnormally low PRA, or "low renin normotension." Similarly, 18% (2/11) of young patients with essential hypertension but 80% (12/15) of older hypertensives had low PRA. When the older volunteers were controls, however, the incidence of low renin hypertension (LRH) decreased to 53% in the older patients. The use of predominantly young controls for defining normal limits of PRA may result in an overestimate of the incidence of LRH and may contribute to the heterogeneity of LRH.

Inhibition of the renin-aldosterone response to furosemide by indomethacin

In 12 human volunteers, indomethacin was shown to inhibit renal prostaglandin produciton as reflected by RIA of urinary PGE2. The increases in plasma renin activity and plasma and urinary aldosterone following acute furosemide challenge were markedly blunted in the presence of indomethacin. In light of recent development indicating an intimate relationship between prostaglandins and renin release, these results provide further evidence for a pivotal role of renal prostaglandins in modulating the responsiveness of the renin-angiotensin-aldosterone axis in Mam.

Effects of angiotensin II blockade by saralasin in normal man

To evaluate the role of angiotensin II in normal man, sar1-ala8-angiotensin II (saralasin), a specific competitive inhibitor or angiotensin II, was given by graded iv infusion (1-20 microgram/kg/min over 1 h) to 6 healthy young volunteers. Significant angiotensin II-dependence of blood pressure was found only after the combined stimulus of sodium restriction (10 mEq daily for 4 days) and ambulation. Systolic blood pressure fell during saralasin infusion from 106.2 +/- 2.0 to 95.8 +/- 2.9 mm (P less than .05). At the same time, plasma renin activity rose strikingly from 3.3 +/- 0.6 to 21.6 +/- 8.5 ng/ml/h, and then fell to 9.3 +/- 4.9 over the post-infusion hour despite continued ambulation. Peak plasma renin activity correlated well with the simultaneous fall in blood pressure (r = .91; P less than .01), suggesting a compensatory response to the vascular effects of angiotensin blockaded. On an ad lib. diet, saralasin infusion had no consistent effect on plasma renin activity serum potassium, or blood pressure, but in supine volunteers plasma aldosterone increased from 9.8 +/- 2.1 to 16.5 +/- 4.8 ng/dl, an average increase of 55 +/- 17% (P less than .05). Although mena plasma cortisol decresed, individual changes in cortisol did not correlate with changes in plasma aldosterone. These data suggest that saralasin has an agonist effect on basal aldosterone secretion.

Plasma 17alpha-hydroxyprogesterone in spironolactone-treated hypertensives

When measured by a specific radio-assay method which excludes drug interference, plasma 17alpha-hydroxyprogesterone levels were found to be similar in spironolactone treated hypertensives, in untreated hypertensives, and in normotensive volunteers. No in vivo evidence for a significant inhibitory effect of spironolactone on adrenal 11beta, 17alpha and 21 hydroxylases was uncovered.

Steroid profile in a case of adrenal carcinoma with severe hypertension

The case of a young boy who had Cushing's syndrome and severe hypertension in association with metastatic adrenal carcinoma is described. Marked elevation of the mineralocorticoid 11-deoxycorticosterone was demonstrated in the plasma. 11-Deoxycortisol, 17alpha-hydroxyprogesterone, and urinary tetrahydro-11-deoxycortisol and pregnanetriol were also elevated. Aldosterone excretion was low. The data implicate defective 11beta hydroxylation and suggest that excessive 11-deoxycorticosterone production may have been responsible for the hypertension.