Parathyroid hormone and calcium: interactions in the control of renin secretion in the isolated, nonfiltering rat kidney.

The present study was designed to characterize the interaction of calcium and PTH in the control of renin release in isolated rat kidneys perfused in a closed circuit at constant flow. Kidneys were rendered nonfiltering using low perfusion pressures (70 mm Hg) and a hyperoncotic perfusate (100 g/liter BSA). Under these conditions, differences in perfusion pressure were less than 9 mm Hg between control and PTH-treated kidneys over the 50 min of perfusion. In the absence of PTH, renin release was inversely correlated with ionized calcium (Ca2+) concentration, with the highest release of renin noted with 1 mM EGTA and no added calcium. Also, verapamil treatment markedly elevated renin release, even in the presence of 2 mM Ca2+. In contrast, renin secretion was strongly depressed by 20 nM BAY-K8644 in the perfusate. In medium containing normal calcium concentrations (1 mM Ca2+), rat PTH(1-34) induced a 2-fold greater renin accumulation than in the control, non-PTH-treated kidneys. Isoproterenol induced a 5-fold stimulation under the same conditions. In the 0 Ca2+/1 mM EGTA perfusion, PTH did not elevate renin secretion. Renin release in response to PTH in 2 mM Ca2+ was similar to that observed in the 1 mM Ca2+ perfusion. PTH also reversed the effects of BAY-K8644 to suppress renin release. In verapamil-treated kidneys, PTH failed to stimulate renin release. These results indicate that PTH stimulates renin release by a process independent of the baroreceptors and macula densa. The Ca2+ modulation of PTH-induced renin release is consistent with the reported ability of PTH to block calcium channels and relax vascular smooth muscle.