The cellular origins of corticotropin and melanotropin as revealed by immunochemical staining.

The cellular origins of corticotropin and melanotropin were studied by observing the response of the rat hypophysis to adrenalectomy and cortisol administration when stained immunochemically with peroxidase-labeled antibody following application of antiserums to P1-24-corticotropin, pp17-39-corticotropin, human p-melanotropin, and a-melanotropin. The presence of corticotropin in the pars intermedia is indicated since this lobe, in addition to corticotropic cells of the pars distalis, stained with antiserum to pp17-39-~orti~otropin. However, the concentration of corticotropin is less in the pars intermedia than in corticotropic cells since at higher dilutions of antiserum the latter cells stained intensely while the pars intermedia was unstained. Also, corticotropic cells exhibited striking hypertrophy after adrenalectomy and regression after cortisol administration, while morphological and tinctorial properties of the pars intermedia were minimally altered. These observations suggest that the pars distalis is primarily responsible for supplying the corticotropin required to meet the changing requirements of the body. With antiserum to human P-melanotropin, the pars intermedia stained intensely. Since the antiserum was ineffective after absorption the staining reaction appears to be specific for p-melanotropin. Except for a rare cell, the pars distalis did not stain. Thus p-melanotropin is restricted primarily to the pars intermedia. Sever a1 observations implicate the pars intermedia of the rat hypophysis in the secretion of corticotropin. First, both parenchymal cells of the pars intermedia (Purves and Bassett, ’63) and many corticotropic cells (Hess et al., ’68; Baker et al., ’70) of the pars distalis stain with aldehydefuchsin and the periodic acid-Schiff procedure, indicating a similarity in their chemical composition. Second, with electron microscopy two types of cells have been described in the pars intermedia (Kurosumi et al., ’61; Porte et al., ’71) and Kobayashi (’65) found enlargement and accumulation of vesicles in “light” cells of the pars intermedia after adrenalectomy. Third, as revealed by labeling of DNA with “-thymidine followed by autoradiography, Gosbee et al. (’70) reported an increase in the labeling index of the pars intermedia after adrenalectoniy and a decrease after cortisol administration, these situations being accompanied by an elevation and a decline, respectively, in the pituitary corticoAM. J. ANAT., 134: 393-410. tropin content. Also in microscopic sections prepared with histological staining procedures, they observed a n increased number of “da rk cells in the pars intermedia after adrenalectomy and no cytological change in the pars distalis. Fourth, all investigators who have utilized immunofluorescence or immunohistochemical procedures for demonstrating the cellular origin of corticotropin have observed that the pars intermedia stains in addition to corticotropic cells of the pars distalis. This result has been obtained with antiserums to up-corticotropin (Nakane, ’70; Baker et al., ’70) , synthetic , t ? 1 2 4 ~ ~ r t i ~ ~ t r ~ p i n (Hess et al., ’68), and p p i 7 3 9 ~ ~ r t i ~ ~ t r ~ p i n (Phjfer and Spicer, ’70). Prior attempts to correlate changes in corticotropin content with cytology of the hypophysis have been unsuccessful when histological staining techniques were used 1 Supported in part by NIH grant HD-03159-04. 2 Present address: Instituto de Nutriciio, Universidade Federal de Pernambuco, Recife, Pernambuco, Brazil.