Influence of Ionic Environment on the in Vitro Synthesis and Release of Pituitary Hormones

Abstract

The incorporation of leucine-4,5-3H into growth hormone and prolactin by rat anterior pituitary glands incubated in buffers of Krebs-Ringer-bicarbonate (KRB), Krebs-Ringerphosphate (KRP) and tissue culture Medium 199 was measured. In KRP prolactin synthesis and release was greatly decreased compared to that found using KRB, whereas growth hormone synthesis and release proceeded equally well in either buffer. Addition of HCO3− to KRP buffer increased greatly the release and synthesis of prolactin. When potassium was omitted from the buffers, a decrease in incorporation of radioactive leucine into prolactin and growth hormone was observed. The absence of Ca++ from KRB greatly diminished prolactin synthesis and decreased release, and similar but less dramatic effects were found using Ca++-free KRP buffer. Growth hormone synthesis and release was decreased by incubation in Ca++-free KRB, but when the calcium was omitted from KRP buffer, a decrease in the release of growth hormone was not accompanied by a decrease in synthesis of the hormone. When the concentration of K+ in Medium 199 was increased 5-fold, no effect on leucine incorporation into prolactin was observed but a 214% increase in growth hormone release occurred. A 5-fold increase in Ca++ concentration increased the synthesis and release of prolactin without affecting the synthesis of growth hormone. It is concluded that changes in the in vitro ion environment of the anterior pituitary gland cause selective changes in the incorporation of leucine-4,5-3H into prolactin and growth hormone and their subsequent release. (Endocrinology86: 863, 1970)