Calcium Dependence of the Inhibitory Effect of Angiotensin on Renin Secretion in the Isolated Perfused Kidney of the Rat

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(NH(2))'-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