Stimulation of renin secretion and calcium efflux from the isolated perfused cat kidney by noradrenaline after prolonged calcium deprivation.

1. The effects of noradrenaline on the secretion of renin and on the efflux of Ca have been investigated in the isolated cat kidney perfused with Locke solution containing the alpha-adrenergic blocking agent, phenoxybenzamine, to block increases in renal vascular resistance. 2. Noradrenaline elicited a marked increase in renin secretion in the absence of any discernible alterations in renal arterial pressure, and prolonged perfusion with Ca-free Locke solution failed to depress noradrenaline-evoked renin secretion. 3. Noradrenaline caused an increase in the efflux of 45Ca from prelabelled kidneys perfused with Ca-free solution. Increasing the noradrenaline concentration produced graded increases in 45Ca efflux and renin release, and the peak rise in efflux preceded or coincided with peak renin secretion. 4. DL-Propranolol inhibited the increase in 45Ca efflux and renin release resulting from noradrenaline stimulation. 5. Electrical stimulation of the renal nerve enhanced 45Ca efflux and renin release from prelabelled kidneys perfused with noraml Locke solution. 6. These findings provide further support for the view that the process of catecholamine-induced renin secretion involves mobilization of Ca from a cellular site.