CALCIUM DEPENDENCE OF THE INHIBITORY EFFECT OF ANGIOTENSIN ON RENIN SECRETION IN THE ISOLATED PERFUSED KIDNEY OF THE RAT

Abstract

1 The effect of calcium on the inhibition of renin secretion by biologically active angiotensin was investigated in the isolated rat kidney perfused with Krebs-Ringer saline. 2 In the presence of calcium (3.7 mm), asp(NH₂)′-angiotensin II suppressed both basal and isoprenaline-stimulated renin secretion. Renal perfusion pressure, which was increased by the infusion of angiotensin, returned to control levels when isoprenaline was added. 3 When the calcium concentration was reduced to 0.32 mm, the vasoconstriction produced by angiotensin was abolished although the inhibitory effect on renin secretion was still evident. 4 In the absence of calcium, angiotensin no longer suppressed basal renin secretion and a prompt increase in renin secretion occurred when isoprenaline was added. 5 The higher basal renin levels which were observed in calcium-free perfusions, suggest the existence of an intrarenal calcium-dependent mechanism that regulates basal renin secretion. 6 These observations indicate that the inhibitory effect of biologically active angiotensin, on basal and isoprenaline-stimulated renin secretion, is functionally related to the contractor response by its dependence on calcium. The recognition that the renin-producing cells are modified smooth muscle cells supports this association