title: Ca2+ transients induced by thyrotropin-releasing hormone rapidly lose their ability to cause release of prolactin.
abstract: To investigate the relationship of changes in cytosolic free calcium concentrations [( Ca2+]c) caused by TRH to changes in PRL secretion, we simultaneously monitored PRL release and [Ca2+]c, using the fluorescent Ca2+ indicator indo-1, in freshly isolated perifused cells from rat anterior pituitary glands. We found that a 30-sec pulse of 100 nM TRH triggered a transient spike of [Ca2+]c, but prolonged PRL release for up to 30 min; continuous administration of TRH caused a sustained elevation in [Ca2+]c, but the same pattern and amount of PRL release as that caused by the pulse of TRH. PRL secretion was refractory to further pulses of TRH given at 10-min intervals for 40 min, but did respond to a second pulse of TRH given 40 min after the first pulse with no intervening pulses. Pulses of TRH given every 10 min still triggered spikes of [Ca2+]c of the same magnitude as the first pulse, indicating that the cause of the refractory state must occur at a post-receptor step that is after the mobilization of [Ca2+]c. A 30-sec pulse of a high concentration of KCl caused a transient spike of [Ca2+]c and transient, not prolonged, release. Additional pulses of KCl cause progressively less PRL release, although the magnitude of the spikes in [Ca2+]c did not change.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06510.
authors.forename: G J
authors.initials: GJ
authors.lastname: Law
authors.forename: J A
authors.initials: JA
authors.lastname: Pachter
authors.forename: P S
authors.initials: PS
authors.lastname: Dannies
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D005260:Female; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
chemical_list: D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D002118:Calcium