Release of Anterior Pituitary Hormones by Trypsin-pretreated Anterior Pituitary Cells

Abstract

Hormone-secreting cells in the anterior pituitary (AP) gland can be categorized into two groups with respect to spontaneous release. One line of evidence has suggested relatively high spontaneous release of GH and PRL compared to other hormones. We previously reported that brief pretreatment of AP cells with trypsin severely decreased the spontaneous release of GH and PRL, but increased that of ACTH and TSH, and had no apparent effect on that of LH and FSH. The cell-type specific alteration of spontaneous release indicates involvement of trypsin-sensitive-membrane-proteins (TSMPs) in the mechanism of hormone release in the AP gland. In this study, we examined secretagogue- and high-K⁺ stimulated release of AP hormones from trypsin-pretreated cells by using a superfusion system. TRH and high K⁺ did not provoke increased PRL release. Each of the secretagogues and high K⁺ caused a corresponding elevation of other hormones, i.e., TSH, ACTH, LH, and FSH, suggesting that the TRH receptor and voltage-sensitive Ca²⁺ channel remained functional. In addition, GRF and high K⁺ did not result in a corresponding increase in GH release. We concluded that the GH/PRL cell lineage has distinct secretory mechanisms including TSMPs.