Modulation of catecholamine release by endogenous adenosine in the rat adrenal medulla

Adenosine was shown to inhibit norepinephrine (NE) release from sympathetic nerve endings. The purpose of this study was to examine whether endogenous adenosine restrains NE and epinephrine release from the adrenal medulla. T he effects of an adenosine receptor antagonist, 1,3-dipropyl-8-(p-sulfophen yl) xanthine (DPSPX), on epinephrine and NE release induced by intravenous administration of insulin in conscious rats were examined. Plasma catechola mines were measured by HPLC with an electrochemical detector. DPSPX signifi cantly increased plasma catecholamine in both control rats and rats treated with insulin. The effect of DPSPX on plasma catecholamine was significantl y greater in rats treated with insulin. Additional experiments were perform ed in adrenalectomized rats to investigate the contribution of the adrenal medulla to the effect of DPSPX on plasma catecholamine. The effect of DPSPX and insulin on epinephrine in adrenalectomized rats was significantly redu ced compared with that of the controls. Finally, we tested whether endogeno us adenosine restrains catecholamine secretion partially through inhibiting the renin-angiotensin system. The effect of DPSPX on plasma catecholamine in rats pretreated with captopril (an angiotensin-converting enzyme inhibit or) was reduced. These results demonstrate that under basal physiological c onditions, endogenous adenosine tonically inhibits catecholamine secretion from the adrenal medulla, and this effect is augmented when the sympathetic system is stimulated. The effect of endogenous adenosine on catecholamine secretion from the adrenal medulla is achieved partially through the inhibi tory effect of adenosine on the renin-angiotensin system. Copyright (C) 200 1 National Science Council, ROC and S. Karger AG, Basel.