Immunohistochemical localization of adrenocorticotropin and melanocyte stimulating hormone in pars intermedia of rat hypophysis.

Abstract

The sites of production of adrenocorticotropin (ACTH) and melanocyte stimulating hormone (MSH) are studied by the immunoglobulin-peroxidase bridge technique, using antisera prepared against synthetic porcine β 1–24 and β 17–39 ACTH, and bovine β MSH on the rat adenohypophysis. Presence of ACTH all over the pars intermedia (PI) is indicated by staining with antisera βp 1–24 and βp 17-3-9 ACTH. There are darkly stained ACTH cells in the PI and pars tuberalis (PT), similar to those in the pars distalis (PD). With higher dilutions of the ACTH antiserum, staining intensity disappears or reduces markedly in majority of the PI cells, whereas, the ACTH cells in the PI, PD and PT do not vary much in their staining intensity. Therefore, it is concluded that majority of the PI glandular cells (light glandular and dark cells) contain less corticotropin than the ACTH cells. From these observations, it seems to me that the major amount of corticotropin is supplied by the ACTH cells of the PD, PI and PT, and less by the light glandular and dark cells of the PI. The antiserum is ineffective after absorption, so the staining reaction appears to be specific for βp 1–24 and βb 17–39 ACTH.