Hormone Secretion of the Anterior Pituitary Gland After Physical Interruption of All Nervous Pathways to the Hypophysiotrophic Area

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Abstract
Previous studies, in which anterior pituitary tissue was transplanted into the hypothalamus, have shown that only the medial basal hypothalamus, the hypophysiotrophic area (HTA), is capable of maintaining the structure and function of the adenohypophysis. In the present experiments the functional capacity of the HTA was studied after physical interruption of all the nervous pathways coming to this region. A small knife was designed, fixed on the electrode holder of a stereotaxic instrument, and used to cut around the HTA leaving the area in contact with the pituitary by means of the unbroken pituitary stalk. Hormone secretion of the anterior pituitary was assessed by evaluating the structure and function of the target organs 3 -5 weeks after the cut. Thyroid weight and struc -ture were similar to those of intact controls and methylthiouracil treatment induced goiter which histologically resembled that of intact treated controls although thyroid weight did not reach the control levels. The adrenal weight increased, and the lipid distribution in the cortex indicated an enhanced ACTH secretion following deafferentation. However, the corticosterone content of the adrenal venous blood did not show appreciable changes. In a number of animals, adrenal ascorbic acid depletion followed unilateral adrenalectomy 24 hr. or 3 weeks after deafferentation. The weight and structure of the testes were maintained following deafferentation, whereas the weight of the ovaries decreased and 2 types of alterations developed 1) polyfollicular ovaries with constant vaginal estrus, and 2) ovaries with persistent but not fresh corpora lutea and constant vaginal diestrus. These findings suggest that the HTA is capable of autonomous activity as far as basic output of substances is concerned for maintenance of normal pituitary structure and function. It is proposed that 2 levels exist in the hypothalamic control of the anterior lobe. One level would be represented by the HTA which acts directly on the pituitary by its trophic and/or releasing substances carried there by the portal circulation. The nervous structures outside the HTA are considered to be the second level. It is assumed that these structures act on the anterior lobe via the HTA by modulating the function of this area.