1,25-Dihydroxycholecalciferol enhances both the bombesin-induced transient in intracellular free Ca2+ and the bombesin-induced secretion of prolactin in GH4C1 pituitary cells.
In GH4C1 rat pituitary cells, 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] enhances both the synthesis of PRL and the TRH-induced transient increase in cytosolic free calcium ( [Ca2+]i). In the present report we investigated whether 1,25-(OH)2D3 could enhance the effect of the tetradecapeptide bombesin (BBS) in GH4C1 cells. Pretreatment of the cells with 1 nM 1,25-(OH)2D3 for 24 h enhanced the BBS-induced transient increase in [Ca2+]i compared to that in control cells, while having no significant effect on the plateau phase of [Ca2+]i. Addition of the Ca2+ channel blocker nimodipine or chelating extracellular Ca2+ with EGTA did not abolish the enhancement of the BBS response in 1,25-(OH)2D3-pretreated cells. Furthermore, the BBS-induced efflux of 45Ca2+ from cells preequilibrated with 45Ca2+ was larger in cells treated with 1,25-(OH)2D3. Incubating GH4C1 cells with 1,25-(OH)2D3 alone or in combination with BBS for up to 72 h did not stimulate synthesis of PRL. However, the BBS-induced secretion of PRL was enhanced in cells pretreated with 1,25-(OH)2D3 for 24 h compared with that in vehicle-treated control cells. The effect of 1,25-(OH)2D3 on BBS-induced secretion was dose dependent, with 10(-11) M 1,25-(OH)2D3 enhancing the stimulated secretion of PRL. We conclude that in GH4C1 cells, pretreatment with 1,25-(OH)2D3 enhances the BBS-induced transient increase in [Ca2+]i. This effect may be due to a modulation of the availability of sequestered intracellular Ca2+ and/or membrane Ca2+ conductance. Furthermore, pretreatment with 1,25-(OH)2D3 enhanced secretion of PRL stimulated by BBS. The enhanced transient increase in [Ca2+]i may be the factor inducing the enhanced BBS-induced secretion of PRL.
Törnquist
K
K
Endocrine Research Laboratory, University of Helsinki, Minerva Foundation Institute for Medical Research, Finland.
D000818:Animals; D001839:Bombesin / Q000494:pharmacology*; D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D004347:Drug Interactions; D004533:Egtazic Acid / Q000494:pharmacology; D009553:Nimodipine / Q000494:pharmacology; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology
D004533:Egtazic Acid; D009553:Nimodipine; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D002117:Calcitriol; D001839:Bombesin; D002118:Calcium