Anatomical, gender, and physiological differences in prolactin secretion from individual pituitary cells of chickens

Abstract

Prolactin (PRL) is a hormone secreted by the anterior pituitary gland. It is involved in a variety of physiological processes such as mammary development and lactation, immune response, metabolism, incubation and parental behavior and crop milk formation. Its secretion in avian species is regulated mainly by stimulatory substances such as vasoactive intestinal peptide. PRL secretion varies with gender and physiological state of the animal. In addition, PRL protein is localized to the cephalic lobe of the anterior pituitary. The cellular basis for these differences is not known. We hypothesize that these differences are due to variations in the proportions of lactotrophs or to the amount of hormone secreted per cell. The objective of this work was to study differences in PRL secretion using the reverse hemolytic plaque assay, which measures hormone secretion at the level of individual cells. We report that increased PRL secretion due to gender (females greater than males), anatomic distribution (cephalic greater than caudal lobe) and physiological state (incubating greater than laying eggs) were concomitant to increased proportions of PRL-secreting cells. Indeed, females had 75% more lactotrophs than males, nearly all of these PRL-secreting cells were located in the cephalic lobe, and incubation behavior was associated with a nearly 2-fold increase in the abundance of PRL secretors. In addition, during incubation behavior, PRL-secreting cells had increased plaque area due to a greater secretory capacity, and the increase in PRL secretors was localized to the cephalic and middle regions of the anterior pituitary. We conclude that differences in PRL secretion are due, at least in part, to changes in the proportions of pituitary cells that release PRL. Regulation of cellular phenotype represents a level of control for PRL secretion in addition to those previously recognized.