Secretion of catecholamines from the perfused adrenal gland of the rat is not regulated by alpha-adrenoceptors.

The question of local regulation of catecholamine secretion by alpha-adrenoceptors of either presynaptic splanchnic nerve terminals or postsynaptic chromaffin cells was investigated in the isolated perfused adrenal gland of the rat. The most selective agonists and antagonists of alpha-adrenoceptors such as clonidine, phenylephrine, yohimbine, etc. did not modify the secretion of catecholamines evoked by splanchnic nerve stimulation or nicotine. It is concluded that the negative feedback mechanism that controls the release of norepinephrine at the central and peripheral noradrenergic synapses does not operate in the adrenal medulla to locally control the secretion of medullary hormones.