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Regulation of prolactin, thyrotropin subunit, and gonadotropin subunit gene expression by pulsatile or continuous calcium signals

, : Regulation of prolactin, thyrotropin subunit, and gonadotropin subunit gene expression by pulsatile or continuous calcium signals. Endocrinology 133(5): 2055-2061

The importance of calcium (Ca2+) influx in increasing the steady-state concentrations of mRNAs coding for the pituitary peptides prolactin (PRL), gonadotropin alpha -subunit and thyrotropin (TSH), LH and FSH beta -subunits was investigated. Adult female rat pituitaries were dissociated, plated for 48 h, then inserted into perifusion chambers. Secretory responses were measured after 2 and 22 h of perifusion. After 24 h cells were recovered, total RNA was extracted and mRNAs were assayed using dot blot hybridization. The 1st experiment examined the effect of the Ca2+ channel blocker verapamil (100 micro M) on the stimulatory action of pulsatile thyrotropin releasing hormone (TRH) (4 nM; 60-min interval) or gonadotropin releasing hormone (GnRH) (100 pM; 60-min interval) on pituitary mRNAs. TRH pulses induced a significant increase (49-56%) in PRL, gonadotropin alpha -subunit (64%) and TSH beta (50%) mRNAs, but not in LH beta mRNA. The effects of pulsatile TRH or GnRH were eliminated when verapamil was added to the medium, suggesting that the Ca2+ influx is critical to the stimulatory action of TRH or GnRH. The 2nd experiment examined the effect of pulsatile vs. continuous increases in intracellular Ca2+ on pituitary mRNA expression. Pulsatile Ca2+ signals were produced by giving 60-min pulses of 50 mM KCl, Bay K 8644 (10 micro M) or Bay K 8644 (10 micro M; in the presence of 10 mM KCl in the injectate) and vehicle pulses to controls. Continuous increases in intracellular Ca2+ were induced by perifusion with medium containing the Ca2+ ionophore A23187 (20 micro M) and these groups were compared with that receiving continuous verapamil. Pulsatile increase in Ca2+ influx (KCl or Bay K 8644) stimulated significant elevations in all mRNAs studied (36-74% increase vs. controls), with the exception of TSH beta . The magnitude of the mRNA responses to pulsatile Ca2+ (vs. controls) was similar to that observed after TRH and GnRH pulses. In contrast, only LH beta was increased by A23187 (42% increase vs. controls; P<0.05). PRL and gonadotropin alpha -subunit mRNAs were selectively diminished by A23187 (57 and 83% decreases vs. controls respectively; P<0.05) and verapamil (67 and 60%; P<0.05). The data show that expression of these pituitary genes is regulated by Ca2+, and that a pulsatile Ca2+ signal is required to stimulate PRL, gonadotropin alpha -subunit and FSH beta (but not LH beta ). Further, PRL and alpha -subunit mRNA expression is particularly sensitive to the pattern of Ca2+ signals, with continuous increases or decreases being inhibitory. Thus, in pituitary cells, pulsatile alterations in intracellular Ca2+ concentrations may be important in the transduction of signals from the plasma membrane to the gene.

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Accession: 002477241

PMID: 8404653

DOI: 10.1210/endo.133.5.8404653

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