Beta-adrenoceptor activation mediates stress-induced secretion of beta-endorphin-related peptides from intermediate but not anterior pituitary.

Recently, we reported that adrenaline can stimulate the secretion of immunoreactive beta-endorphin in the rat. This response is mediated by beta-adrenoceptors and requires circulating adrenaline concentrations which are known to occur during stress. We therefore studied whether catecholamines are implicated in the stress-induced secretion of immunoreactive beta-endorphin from the pituitary gland. We report here that in rat the beta-adrenoceptor antagonist (-)propranolol reduces or abolishes the rapid increase of immunoreactive beta-endorphin levels during some stress stimuli (footshock, passive avoidance, restraint) but not during others (ether, formalin, laparotomy). The propranolol-sensitive response is largely prevented by extirpation of the neurointermediate lobe of the pituitary gland but is unaffected by dexamethasone, which inhibits peptide secretion from the corticotroph cells of the anterior lobe. These results suggest that catecholamines activate the release of immunoreactive beta-endorphin from the intermediate lobe but not from the anterior lobe of the pituitary gland during certain stress conditions.