Effect of intracerebroventricular administration of opioid peptides on basal serum adrenaline levels in conscious rats.

It is considered that adrenomedullary secretion of adrenaline is centrally regulated by various endogenous substances. Recently, opioid peptides have been reported as one of this group of endogenous substances. However, the receptor through which these endogenous opioid peptides regulate adrenomedullary adrenaline secretion has not been elucidated. In the present study, various opioid peptides were administered intracerebroventricularly in conscious, unrestrained rats, and blood catecholamine levels were measured at various periods to determine which cerebral opioid peptide receptor is involved in the mechanism of basal adrenomedullary adrenaline secretion. The results indicate that delta-receptor stimulation has a positive effect on basal adrenomedullary adrenaline secretion, while mu- and kappa-receptors are not involved in this mechanism.