THE POSSIBILITY OF A DIRECT 'INTERNAL' FEEDBACK IN THE CONTROL OF PITUITARY GONADOTROPHIN SECRETION

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Abstract
The gonadotrophin content of the pituitary of intact mature female rats decreases considerably after treatment with pregnant mare serum (PMS) (Szontágh, Uhlarik & Jakobovits, 1963). This phenomenon might be explained by assuming that gonadotrophins act on the hypothalamus, not only by mediation of the gonads, but also directly. The possibility that a direct 'internal' feedback of this kind exists was recently discussed by Szentágothay, Flerkó, Mess & Halász (1962), and has actually been proved with respect to the regulation of ACTH secretion. Sawyer & Kawakami (1961) have suggested that a direct feedback mechanism exists between the hypothalamus and the adenohypophysis, also involving the gonadotrophic hormones. Török (1962) reported the existence of a two-directional blood-flow in the portal vascular system of the adenohypophysis, to and from the hypothalamus, thus demonstrating the anatomical route by which chemical mediators might pass between the pituitary and the hypothalamus. In previous investigation on intact animals

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