Effect of the isolated removal of the median eminence (ME) and pituitary stalk (PS) on the immunohistology and hormone release of the anterior pituitary gland grafted into the hypophysiotrophic area (HTA) and/or of the in situ pituitary gland.

Isolated removal of the median eminence (ME) and pituitary stalk (PS) of female rats was performed under visual control, using a new instrument to open up the 3rd ventricle. Atrophy of the uterus, the follicles and the intersitial tissue in the ovaries was accompanied by persistent corpora lutea and persistent diestrous vaginal smears in rats which had undergone a successful removal of ME and PS. No change was, however, detected in the weight of the thyroid and adrenal glands at the end of the six weeks experimental period. An adenohypophysis implanted in the place of the ME at the time of the surgery, could not prevent these changes. In animals, in which the removal of the ME was not complete, the changes of the gonadal system were less pronounced. Immunocytology of the pituitary LH-, FSH, TSH- and prolactin-cells in animals with completely removed ME and PS showed inactive LH- and FSH-cells both in the grafted and in situ pituitaries, while the TSH- and prolactin-cells appeared to be in a stimulated state. In animals with ME remnant, LH-RH axon terminals were localized only on the blood vessels of the remnant. The part of the pituitary graft in contact with these blood vessels, as well as some areas of the in situ pituitary gland, contained active LH cells as judged from their size and immunohistological appearance. Since in the absence of the ME, the hypophysiotrophic area is not able to exert its regulatory effect on the gonadotrophs of the pituitary implant in this area, the authors suggest that this effect is mediated by the blood circulation of the ME which is rich in releasing hormones and is drained toward both the anterior pituitary and the medial basal hypothalamus.