Thyrotropin-releasing Hormone Stimulation of Prolactin Release from Clonal Rat Pituitary Cells

Abstract

A B S T R A C T Thyrotropin-releasing hormone (TRH)stimulates prolactin release and 45Ca2+ efflux from GH3 cells, a clonal strain of rat pituitary cells. Elevation of extracellular K+ also induces prolactin release and increases 45Ca2+ efflux from these cells. In this report, we distinguish between TRH and high K+ as secretagogues and show that TRH-induced release of prolactin and 45Ca2+ is independent of the extracellular Ca21 concentration, but the effect of high K+ on prolactin release and 45Ca2+ efflux is dependent on the concentration of Ca2+ in the medium. The increment in 45Ca2+ efflux induced by 50

Thyrotropin-releasing hormone mobilizes Ca2+ from endoplasmic reticulum and mitochondria of GH3 pituitary cells: characterization of cellular Ca2+ pools by a method based on digitonin permeabilization.

“…Stimulated phosphorylation is detected at 15 sec, a time scale consistent with the organelle Ca2+ efflux described here. Although our data do not exclude the possibility that TRH may stimulate influx of extracellular Ca2+, the observation that calcium channel blockers fail to inhibit TRH-induced Ca2+ pool depletion is consistent with other studies that indicated a nonobligatory role for Ca2+ influx in TRH stimulation of Ca2" efflux and hormone secretion (3)(4)(5) …”

“…In GH3 cells, a clonal TRH-responsive rat pituitary tumor cell line, TRH-induced 45Ca2+ efflux was shown to be independent of extracellular Ca21 (3,5). In addition, it has been found that stimulation of prolactin release by TRH may not require extracellular Ca2+ (2)(3)(4)(5) Digitonin Permeabilization of Cells. Cells incubated as above (4Ca2+ steady-state or 45Ca2+ uptake experiments) were centrifuged at 4°C (800 x g, 3 min) and washed once with icecold Na+-, Ca2+-free HBSS (formulated with choline chloride instead of NaCl).…”

“…It has been proposed that TRHstimulated hormone release is the result of a TRH-induced increase in cytosolic Ca2+ concentration (1). Some workers have suggested that TRH promotes influx of extracellular Ca2" (1, 2) while others have proposed that the hormone mobilizes intracellular Ca2+ (3)(4)(5). In GH3 cells, a clonal TRH-responsive rat pituitary tumor cell line, TRH-induced 45Ca2+ efflux was shown to be independent of extracellular Ca21 (3,5).…”

“…Some workers have suggested that TRH promotes influx of extracellular Ca2" (1, 2) while others have proposed that the hormone mobilizes intracellular Ca2+ (3)(4)(5). In GH3 cells, a clonal TRH-responsive rat pituitary tumor cell line, TRH-induced 45Ca2+ efflux was shown to be independent of extracellular Ca21 (3,5). In addition, it has been found that stimulation of prolactin release by TRH may not require extracellular Ca2+ (2)(3)(4)(5) Digitonin Permeabilization of Cells.…”

Prostaglandin E2-Induced Luteinizing Hormone- Releasing Hormone Release Involves Mobilization of Intracellular Ca+2*

“…Finally, it must be pointed out that mobilization of intracellular Ca +2 as a mechanism of secretagogue action is not without precedent, as it has been recently shown to mediate TRH-induced PRL release from normal pituitary cells and clonal pituitary cell lines (40)(41)(42). Examination of the mechanism by which PGE 2 may mobilize intraterminal Ca +2 in the ME warrants further investigation.…”