Effects of naloxone on basal and stress-induced prolactin secretion, in intact, hypothalamic deafferentated, adrenalectomized, and dexamethasone-pretreated male rats.

The effects of naloxone (Na1) on basal and stress-induced PRL secretion were investigated in intact (N) adult male rats, as were its effects in rats with complete hypothalamic deafferentation (CHD), in adrenalectomized (adrenX) rats, and in rats pretreated with dexamethasone (dex). Forty-five minutes subsequent to Na1 administration (5 mg/kg, BW, IP) basal serum levels of PRL were reduced by approximately 25% (p less than 0.05), in both N and CHD groups. PRL secretory responses to acute exposure to both photic and acoustic stress wee markedly attenuated in Na1-injected, as compared to vehicle-injected animals. Basal serum PRL concentrations were elevated by 40% in adrenX rats (p less than 0.05), as reduced by 25% (p less than 0.05) in dex-treated rats, as compared to controls. In both these experimental groups, Na1 administration caused significant reductions in serum PRL. This study demonstrates that stress-induced, as well as basal PRL secretion, is attenuated by Na1, and points to a hypothalamic site of action in this regard. Furthermore, these Na1 effects are independent of glucocorticoid interactions with the CNS.