A study of certain of the central effects of sexual hormones: with special reference to the mammary glands)

The central effect of oestrogen on prolactin release has been demonstrated in both female and male rats. The results obtained show that the ME region which includes, in the present study, the arcuate nucleus and the rostral area of the mamillary bodies, seemed to be the centre sensitive to oestradiol implantation. The anterior pituitary has also been found to be sensitive to oestrogen in promoting prolactin release.The presence or absence of corpora lutea in the ovaries of female rats was found to be responsible for the type of mammary gland growth which could be obtaihed by implanting oestradiol in the ME region or the anterior pituitary. Full mammary gland development and milk ejection was only observed when progesterone secretion was present. On the other hand, in the absence of progesterone (i.e., in rats with follicular ovaries devoid of corpora lutea) oestrogen implantation induoed marked duct development and the absence of lobulo-alveolar growthIn male rats the presence of absence of testosterone during the first days of life seemed to influence the development of the mammary gland in later life. The response of the mammary gland to prolactin released by oestrogen implantation was also dependent on the effect of testosterone in the first 24 hours after birth. When oestrogen was placed in the basal tuberal region or the adenohypophysis of male rats in which testosterone was present during the first few days of life, the dense cluster of alveoli (normal structure in the male mammary gland) developed into large cystic formations distended with secretion.In the male rat castrated at birth in which the normal mammary gland structure is not present, the effect of prolactin released under the central influence of oestrogen, was to induce mammary gland growth similar to that observed in constant oestrous female rats. The presence of progesterone secreted by an ovarian graft, in these implanted animals induced a mammary gland growth typical of the normal female type.Further studies will be necessary to establish if the anlage of the mammary gland either in female or male rats is dependant on the presence or absence of testosterone during the first 24 hours of life.Work in progress shows that high levels of circulating progesterone prevents or regulates (dose dependant) the release of prolactin induced by the placement of oestrogen in the hypothalamus or adenohypophysis. It has already been shown that the administration of progesterone (0.4 rag every other day) inhibited the central]of oestrogen in inducing prolactin release, and that the amount of progesterone secreted by the new set of corpora lutea, induced by the administration of HCG to the constant oestrous rats, prevented secetion in the developed mammary gland.Results obtained in the present study may provide some evidenoe for the neuro-hormonal mechanisms involved in the mammary gland growth during pregnancy in the rat