Response of prolactin, growth hormone and corticosterone secretion to morphine administration or stress exposure in Wistar-AVN and Long Evans rats.

The effect of exposition to novel environment or of morphine administration on the release of prolactin, growth hormone and corticosterone by rats of a strain exhibiting high sensitivity to acoustic epileptogenic stimulus (Wistar-AVN) was compared to that of normally sensitive rats of the Long Evans strain. Novelty stress for 15 min resulted in an enhanced prolactin secretion in Long Evans rats only, whereas morphine administration (6 mg kg-1) increased plasma prolactin levels in both strains, the response of the Long Evans animals being significantly higher. The stress-induced inhibition of growth hormone was observed in Long Evans rats only, whereas the morphine stimulated plasma growth hormone increase was observed in animals of both strains. In stress, the corticosterone release was significantly more pronounced in Long Evans than in Wistar-AVN rats. After morphine administration no significant enhancement of corticosterone release was observed in either strain, but in the Long Evans animals the post-morphine values were significantly higher than in the Wistar-AVN rats. The results show a weaker endocrine activation in Wistar-AVN than in Long Evans rats and suggest different neuroendocrine responsiveness of the animals of these strains to exogenous stimuli.