Effect of Hypothalamic Lesions on Pituitary Prolactin Content in the Rabbit

Abstract

Hypothalamic lesions have been shown to induce lactation, but their mechanisms of action have not been understood. In the present study the effects of lactation-inducing hypothalamic lesions on pituitary prolactin were assessed in mature New Zealand female rabbits. The rabbits were ovariectomized and primed 10 days with estradiol benzoate. On day 12 an electrolytic lesion was placed in the basal hypothalamus, and autopsy was performed on day 15. Mammary gland activation was classified both grossly and by histologic examination. Pituitary prolactin was assayed by an intradermal crop sac method employing White King squabs. In rabbits which failed to show mammary gland activation, the lesions lay outside the posterior tuberal area, and pituitary prolactin content was high. Conversely, the mammary glands were markedly activated in rabbits with lesions involving the posterior tuber, and pituitary prolactin was low. Results indicate that the activation of mammary glands by hypothalamic lesions is an effect exerted on the release of pituitary prolactin rather than an influence upon its synthesis.