Further Studies on the Hormone Secretion of the Anterior Pituitary Transplanted Into the Hypophysiotrophic Area of the Rat Hypothalamus

Abstract

Anterior pituitary tissue was transplanted into different parts of the hypothalamus and other parts of the brain or under the renal capsule in hypophysectomized male and female rats. Hormone secretion by the grafted pituitary was assessed by evaluating the structure and function of the gonads, thyroids and adrenals 2-3 months after grafting. The state of the target glands depended entirely on the location of the pituitary transplant. If the pituitary was situated in the medial basal hypothalamus (the hypo-physiotrophic area) gonadotropic hormone secretion was nearly normal: the weight of the ovaries was normal and they contained ripe follicles and fresh corpora lutea; vaginal smears revealed the reappearance of nearly normal cycles after variable time intervals following hypo-physectomy and pituitary transplantation; anterior hypothalamic lesions induced constant estrus, and compensatory hypertrophy of the ovary developed following unilateral ovariectomy. Direct contact with the capillary loops of the median eminence was not necessary for the preservation of gonadotropic hormone secretion by the transplanted pituitary. The weight and histological structure of the thyroid and adrenal glands, as well as the corticosterone content of the adrenal venous blood, were also more or less preserved in animals bearing the pituitary graft in the medial basal hypothalamus. However, compensatory hypertrophy of the adrenals following unilateral adrenalectomy as well as goiter subsequent to methylthiouracil treatment was observed only in those animals in which the pituitary graft was connected with the median eminence. In animals with pituitary grafts outside the medial basal hypothalamic region, the gonads, thyroids and adrenals were atrophied and resembled those of hypo-physectomized controls. The experiments support the previous suggestion that the hypophyslotropic area of the hypothalamus produces some substances essential for normal pituitary structure and function. It is suggested that these substances are carried by the tubero-infundibular tract to the zone in contact with the pituitary circulation. The differences in gonadotropic, thyrotropic and adrenocorticotropic hormone secretion of the pituitaries situated within the hypophysio-tropic area are discussed.