[Effect of clonidine on the function of adrenal medulla in rats (author's transl)]

The present experiments were undertaken to elucidate the effect of clonidine on the function of adrenal medulla both in normotensive rats and spontaneously hypertensive rats (SHR). In urethane anesthetized rats, efferent discharge rate of splanchnic nerve and sympathetic adrenal nerve branch (adrenal nerve) was recorded. Plasma catecholamine concentration of adrenal venous blood was determined radioenzymatically. Catecholamine secretion rate from left adrenal gland was calculated. In normotensive rats, clonidine produced a significant decrease in efferent nerve activity of the splanchnic nerve and adrenal nerve. It was also demonstrated that clonidine produced a significant decrease in adrenaline secretion rate from adrenal gland. Statistically insignificant decrease in noradrenaline secretion rate from adrenal gland was observed. Clonidine induced hyperglycemia was not related to the rapid fall in adrenal efferent nerve activity induced by clonidine. In debuffered rats, clonidine produced a decrease in the adrenal efferent nerve activity. In SHR, clonidine produced a significant decrease in adrenal efferent nerve activity and adrenaline secretion rate from adrenal gland. With regard to the response of adrenal efferent nerve activity to clonidine, decreased activity appeared more remarkably in normotensive rats as compared with that in SHR. These findings suggest that clonidine decreases adrenaline secretion rate from the adrenal glands by central actions in rats.