Identification of the corticotropin cell in rat hypophyses with peroxidase‐labeled antibody

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 in 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.