THE PROLACTIN PRODUCTION AND RELEASE OF A PITUITARY GRAFT AND OF THE HYPOPHYSIS IN SITU

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Abstract
In order to compare the prolactin function of a pituitary graft with that of a hypophysis in situ, an attempt was made to make the two groups of experimental animals used comparable with respect to their gonadotrophin and steroid levels. This was done by autotransplantation of the ovaries into the spleen or by ovariectomy, and by supplying excess amounts of exogenous gonado-trophins. It was found that prolactin effects produced by hypophyseal grafts were far greater than those brought about by hypophyses in situ. If small amounts of estrogens accidentally escaped from the portal circulation, these effects were enhanced both in the grafted animals and in those with the hypophyses in situ. Assays of serum and hypophyseal material of ovariectomized and hypophysectomized rats bearing a hypophyseal graft under the kidney capsule showed that the prolactin content of the graft is lower and the prolactin content of the serum higher when compared to material from ovariectomized sham-operated controls. From these results it is concluded that: (1) the hypothalamus inhibits the prolactin function of the hypophysis in situ; (2) hypothalamic inhibitory mechanisms affect prolactin release more than prolactin production; (3) estrogens enhance prolactin production in the hypophysis, presumably mainly by a direct action on the pituitary gland.