The direct action of 17 p-estradiol and cholesterol on cells of the pituitary pars distalis, as revealed by staining with peroxidase-labeled antibody, was studied in female rats. Pellets of pure cholesterol and of estradiol mixed with cholesterol were implanted into the left lobe of the pars distalis 14-32 days after ovariectomy and left in place for 7-16 days. Rabbit antisera to rat prolactin, human growth hormone, human chorionic gonadotropin (for gonadotropes -presumably luteinizing hormone cells), and porcine corticotropin were used. In no case were cells altered in the contralateral lobe of the pars distalis; cholesterol likewise had no significant effect on the ipsilateral lobe. However, in the ipsilateral lobe containing an estrogen pellet, prolactin cells were hypertrophied and hyperplastic; cells assumed to be responsible for luteinizing hormone secretion were reduced in size and stained more intensely; and growth hormone cells were reduced in size. Corticotropin cells remained unaffected. For the most part estrogenic effects were distributed ventrally, caudally and laterally from the pellet and not far medially, never reaching the midline. It was concluded that estrogen acts directly on the hypophysis, the spread of the effects reflecting the direction of blood flow within the gland. These observations support the hypothesis that the pituitary gland serves as a site for feedback action by estrogen.One of the most important current problems in neuroendocrinology is to ascertain whether the hypothalamus or hypophysis serves as the primary site for feedback action by target-organ hormones. Evidence available at present indicates that both sites are probably responsive to estrogen but the manner in which the functional roles of the hypothalamus and hypophysis are integrated remains unclear.Several investigators have implanted ovarian tissue or estrogen into the hypothalamus and, from the effects observed, concluded that estrogens act primarily on the hypothalamus. Thus, Flerko and Szentitgothai ('57) found that ovarian secretory activity was depressed in rats bearing small intrahypothalamic autotransplants of ovarian tissue, but not in rats bearing intrapituitary implants. Likewise, implantation of estrogen into the median eminence of the rabbit caused depression of ovarian function (Davidson and Sawyer, and elevated the prolactin content of the gland (Kanematsu and Sawyer, '63a). These workers found that estrogen placed into the hypophysis failed to duplicate these effects, the pituitary prolactin content actually being depressed (Kanematsu and Sawyer, 63a).Apparently the rat responds differently to these experimental procedures. After Lisk ('60) showed that estrogen implanted into the hypothalamic arcuate nucleus causes atrophy of the genital tract, McCann and his colleagues found that estrogen located in either the median eminence or hypophysis was effective; such implants prevented the postovariectomy rise in plasma luteinizing hormone (Ramirez Abrams and McCann, '64) and elicited peripheral e...
In order to verify the concept that growth hormone and prolactin are contained in two different populations of acidophils, sections of Bouin-fixed rat hypophyses were stained immunochemically. For this purpose the histochemical demonstration of peroxidase was utilized after sequential application to the tissue section of rabbit antiserum to human growth hormone (or antiserum to rat prolactin) followed by application of peroxidase-labeled sheep antiserum to rabbit gamma-globulin. It was found that growth hormone cells and prolactin cells, when revealed immunochemically, corresponded structurally to cell types that could be differentiated with reasonable certainty in sections stained with the Masson trichrome procedure. When delineated immunochemically, growth hormone cells were larger and more densely arranged in the adult male than in the intact female; thcy exhibited little change in the female after ovariectomy. In contrast, prolactin cells were large and frequent in the female hypophysis but were small and less frequent in the male and in the female after ovariectomy. By double-staining, growth hormone and prolactin cells were differentiated in the same section. It was concluded that ( a ) growth hormone and prolactin are contained in, and presumably secreted by, two different populations of acidophils; and ( b ) the Masson procedure permits a reasonably accurate differentiation of the two cell types.
Utilization of peroxidase-labeled antibody to porcine corticotropin permitted the delineation of a distinctive cell in the hypophyseal pars distalis of the rat that appears to be the source of corticotropin. Corticotropin cells were stellate and possessed processes that ended on the walls of sinusoids. Corticotropin cells composed a small percentage of the total cell population, and were distributed throughout the gland except that they were less common posteriorly, superiorly, and immediately alongside the pars intermedia. Alteration i n size of corticotropin cells was related directly to change in corticotropin content of the gland as effected by differing physiological conditions. Thus, they were larger in the female than in the male and were enlarged after adrenalectomy of the male; they became much smaller following treatment of the female with cortisol. Some corticotropin cells stained with aldehyde fuchsin and the periodic acid-Schiff (PAS) reaction. These reactions were more intense if hormone antibody and the gamma-globulin conjugate had been applied previously. However, the capacity of some corticotropin cells to stain weakly with PAS without prior application of antibody suggests that they may contain mucoprotein.The cellular origin of corticotropin remains undetermined, its secretion having been attributed to each of the major cell classes found in the hypophyseal pars distalis. Finerty and Briseno-Castrejon ('49) drew attention to acidophils as a possible source of corticotropin by observing an increase in their relative number after subjection of hemi-adrenalectomized rats to stress. This conclusion was later supported by Herlant and Klastersky ( ' 6 3 ) who reported an increase in the number of pituitary acidophils containing small granules (about 100-150 mp in diameter) in hypophyses made hyperactive by administration of a chemical inhibitor of corticosteroidogenesis. Utilizing fluorescein-labeled antibody to synthetic p'-"-corticotropin, Kracht et al. ('65) also localized corticotropin in acidophils of the rat. On the other hand, Siperstein ('63) combined radioautography with chemical staining after administration of labeled glycine to identify a hyperactive cell in adrenalectomized rats which she believed to be a chromophobe and the source of corticotropin.ANAT. REC., 166: 557-5138.
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