Effects of the renin-angiotensin system on the reflex response of the adrenal medulla to hypotension in the dog.

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We have studied the influence of the renin-angiotensin system on the control of catecholamine release from innervated and denervated adrenal glands of anaesthetized dogs. Captopril reduced the resting release of catecholamines and inhibited release evoked either by lowering carotid sinus pressure or by stimulating the peripheral end of the cut splanchnic nerve. Both responses were restored by exogenous angiotensin II, and the reflex response could also be restored by corticotrophin. Cycloheximide, in the presence of captopril, further reduced the resting release of catecholamines and prevented the restoration of the reflex response by angiotension II. Plasma renin activity did not rise during baroreceptor tests lasting 10 min, but catecholamine release was evoked from the first minute. We conclude that the response of the adrenal medulla to sympathetic activity requires a minimum circulating concentration of angiotensin II. It is severely impaired by inhibition of the renin-angiotensin system but function can be restored either by exogenous angiotensin II or by corticotrophin.

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