INFLUENCE OF 17-$\alpha$-ESTRADIOL ON CATECHOLAMINE SECRETION FROM THE PERFUSED RAT ADRENAL GLAND

It has been known that adrenal corticosteroids influence the expression of adrenomedullary catecholamine-synthetizing enzymes and also suppress the emission of axonal-like processes in cultured chromaffin cells. In the present study, it was attempted ta investigate the effect of 17${\alpha}$-estradiol on catecholamine(CA) secretion evoked by acetylcholine(ACh), DMPP, McN-A-343, excess K$\^$+/ and Bay-K-8644 from the isolated perfused rat adrenal gland. The perfusion of 17${\alpha}$-estradiol (10$\^$-6/ 10$\^$-4/M) me an adrenal vein for 20min produced relatively dose-dependent inhibition in CA secretion evoked by ACh (5.5 ${\times}$ 10$\^$-3/M), DMPP (10$\^$-4/M for 2min), McN-A-343 (10$\^$-4/M for 4min) and Bay-K-8644 (10$\^$-5/M for 4min), while did not affect the CA secretory effect of high K$\^$+/(5.6 x 10$\^$-2/M). Also, in the presence of 17${\beta}$-estradiol, CA secretion of ACh, DMPP and McN-A-343 without any effect on excess K$\^$+/-evoked CA secretion. However, in adrenal glands preloaded with 17${\alpha}$-estradiol (10$\^$-5/M) plus tamoxifen (10$\^$-5/M), which is known to be a selective antagonist of estrogen receptors (for 20min), CA secretory responses evoked by ACh, DMPP and McN-A-343 were considerably recovered as compared to that of 17${\alpha}$-estradiol only, but excess K$\^$+/-induced CA secretion was not affected.