TRH (thyrotropin-releasing hormone) and BAY K 8644 synergistically stimulate prolactin release but not sup 45 Ca sup 2+ uptake
- Yale Univ. School of Medicine, New Haven, CT (USA)
Thyrotropin-releasing hormone (TRH) and the Ca{sup 2+}-channel agonist BAY K 8644 each induced transient increases in prolactin secretion from primary cultures of rat anterior pituitary cells in perfusion. When BAY K 8644 was added after a TRH-induced secretory peak, the additional effect of BAY K 8644 on prolactin release was approximately twofold greater over a 30-min period than the effect of BAY K 8644 on previously untreated cells. TRH and BAY K 8644 were also synergistic when added in the opposite order or simultaneously. Substitution of other agents for BAY K 8644 revealed that only high K{sup +} was at least additive with TRH in stimulating prolactin secretion; treatment with TRH inhibited, rather than facilitated, subsequent stimulation of prolactin secretion by angiotensin II or the ionophore A23187. The cooperative effect was not specific for TRH because BAY K 8644 also acted synergistically with angiotensin II or 40 mM K{sup +}. In GH{sub 4}C{sub 1} cells, in which TRH and BAY K 8644 were also synergistic in releasing prolactin, measurements with the fluorescent indicator indo-1 showed that TRH and BAY K 8644 could each elevate cytosolic Ca{sup 2+} above the level stimulated by the other. Unexpectedly, TRH was found to inhibit BAY K 8644-stimulated {sup 45}Ca{sup 2+} uptake in both GH{sub 4}C{sub 1} and primary cultured cells. These results indicate that BAY K 8644 and TRH synergistically stimulate prolactin secretion by a mechanism other than a cooperative effect on the activity of dihydropyridine-sensitive Ca{sup 2+} channels.
- OSTI ID:
- 6037128
- Journal Information:
- American Journal of Physiology; (USA), Vol. 255:5; ISSN 0002-9513
- Country of Publication:
- United States
- Language:
- English
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TIME DEPENDENCE
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AUTONOMIC NERVOUS SYSTEM AGENTS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
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551001* - Physiological Systems- Tracer Techniques