Induction of Mammary Secretion by Hypothalamic Lesions in Male Rats1

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Abstract
Hypothalamic lesions in the median eminence (ME), hypophysial stalk, or paraventricular nuclei of male rats produced lobulo-alveolar development and secretion in the mammae. Lesions in the preoptic area and mamillary bodies were ineffective. The time course of these mammary changes was followed in rats with ME or stalk lesions. Mammary development and secretion was apparent at 2 days and reached a maximum at 4 days postoperatively. By 17 days the mammae had regressed to an atrophic condition. At this time weights of testes, seminal vesicles and adrenals were subnormal. The mammary changes seen in rats with hypothalamic lesions could be mimicked by the administration of a total dose of 5.0 or more IU of prolactin in 5 subcutaneous (sc) injections spaced over a 48-hr. period. Adrenalectomy performed just prior to placement of ME lesions did not interfere with the development of mammary changes. Castration 7 days prior to location of ME lesions prevented the development of the mammary changes unless the rats were maintained on daily sc injections of testosterone propionate (Tp). Pituitary prolactin content was within normal limits on estimation 48 hr. postoperatively in rats with ME lesions. It is concluded that interruption by hypothalamic control results in increased prolactin synthesis and release in male rats, and that the hypothalamus exerts a tonic inhibitory influence on prolactin secretion in the male as well as the female.