Effect of prostacyclin infusion on active and inactive renin release in the isolated perfused kidney

The significance of autonomic neuropathy in the elevation of inactive renin in diabetes mellitus

Plasma renin activity (PRA) and inactive renin(IR, activated by trypsin) were measured in the plasma of 15 type II diabetics with autonomic neuropathy (group 3), 15 type II diabetics without (group 2), and 14 nondiabetic control subjects (group 1) in the recumbent position. There were no significant differences between the 3 groups with respect to age, ideal body weight, supine resting mean blood pressure, serum creatinine, daily urinary excretion of sodium, or renin substrate at the time of study. Autonomic neuropathy (AN) was assessed by measurement of the ratio of the longest to the shortest R-R interval during deep breathing (E/I-ratio) and by postural hypotension. PRA was significantly lower in group 3 than in group 1 (p less than 0.05). The IR level was significantly higher in group 3 than in groups 2 and 1 (p less than 0.005 for both comparisons). The ratio of active renin to total renin (TR) (PRA/(IR + PRA)) was significantly lower in group 3 than in groups 2 and 1 (p less than 0.001 for both comparisons). The IR level and PRA/(IR + PRA) were significantly correlated with E/I-ratio (r = -0.498, p less than 0.01 and r = 0.588, p less than 0.001, respectively) and with the severity of postural hypotension (r = 0.383, p less than 0.05 and r = 0.401, p less than 0.05, respectively), but not with the daily urinary excretion of protein or 24 h-creatinine clearance (24 h-Ccr) in the whole diabetics. From these results, we conclude that autonomic neuropathy might be a more important factor than nephropathy in the lower PRA and higher IR level in type II diabetics with AN.

Effect of prostacyclin on renal kallikrein release in man

The aim of this research was to study exogenous prostacyclin effect on urinary kallikrein excretion (UKK) in man, to define whether prostacyclin-induced renin release and/or endogenously released cyclooxygenase products were responsible for prostacyclin-induced enhancement of UKK, to determine furosemide effect on UKK. Prostacyclin was infused in eight healthy men and repeated after propranolol and indomethacin treatment. Prostacyclin caused a dose-dependent increase of UKK. Pretreatment with propranolol and indomethacin did not affect prostacyclin-induced enhancement of UKK, although it reduced absolute values of plasma renin activity. Furosemide increased UKK and simultaneously urinary 6-keto-prostaglandin F1 alpha. We conclude that prostacyclin induces an increase in UKK in a dose-dependent manner; furosemide-induced renal prostacyclin synthesis is temporally related to enhancement of UKK; partial dissociation of UKK from plasma renin activity under propranolol and indomethacin treatment and in response to furosemide might suggest a direct effect of prostacyclin on UKK.

Evidence of prostacyclin deficiency in the syndrome of hyporeninemic hypoaldosteronism

Hyporeninemic hypoaldosteronism is an important cause of hyperkalemia and is characterized by low renin secretion. We found that prostacyclin, a potent vasodilator and renin secretagogue, was markedly reduced--as reflected by its stable urinary metabolite 6-keto-prostaglandin F1 alpha--in seven patients with hyporeninemic hypoaldosteronism as compared with seven matched controls with renal insufficiency and as compared with 12 normal volunteers (mean +/- SE, 42 +/- 7 vs. 185 +/- 37 and 164 +/- 20 ng per gram of creatinine, respectively; P less than 0.001). In contrast, renal prostaglandin E2 excretion was similar in all three groups. A low-dose infusion of calcium or norepinephrine (known stimulants of prostacyclin) increased renal prostacyclin release in normal subjects and controls with renal insufficiency. Neither agonist, however, increased the low basal prostacyclin excretion in the patients (49.6 +/- 11 [basal] vs. 62 +/- 20 [norepinephrine] and 47.5 +/- 16 [calcium]; P greater than 0.8). To evaluate the functional importance of the altered prostacyclin production, we studied the responses of renal blood flow and blood pressure to the calcium infusion. The calcium infusion did not alter blood pressure or renal blood flow in the normal subjects or the controls with renal insufficiency. In contrast, the same dose of calcium in the patients with hyporeninemic hypoaldosteronism produced a rise in mean blood pressure (from 91 +/- 6 to 104 +/- 8 mm Hg, P less than 0.05) and a fall in renal blood flow (from 673 +/- 58 to 560 +/- 42 ml per minute per 1.73 m2, P less than 0.05). These results indicate that a deficiency of prostacyclin could explain the low active-renin concentration and altered vasomotor tone seen in hyporeninemic hypoaldosteronism.

Effect of captopril on renal vascular resistance, renin, prostaglandins and kinin in the isolated perfused kidney

Vasodilatory and natriuretic effects of captopril were studied in the isolated hog kidney perfused with modified Krebs-Ringer solution. Renal arterial infusion of captopril caused increases in releases of renin, prostaglandins (PGE2, 6-keto-PGF1 alpha and PGF2 alpha) and kinin, and was accompanied by a decrease in the renal vascular resistance and an increase in urinary sodium excretion. Indomethacin administered with captopril diminished the saluretic effect of captopril and evoked an increase in kinin, but was associated with a marked decrease in prostaglandin and renin releases, while renal vascular resistance remained decreased. Indomethacin alone did not alter vascular resistance and kinin; however, renin and prostaglandin releases were decreased. Aprotinin administered with captopril showed a decrease in releases of prostaglandins, renin and kinin without any change in vascular resistance. These results suggest that increased release of kinin induced by captopril contributes to a reduction in renal vascular resistance. Increased prostaglandin release after captopril administration may be caused by an increase in kinin without direct involvement of captopril in prostaglandin synthesis. Renal prostaglandins may enhance sodium excretion and mediate renin secretion in captopril perfusion.