Prolactin secretion and intracellular Ca(2+) change in rat lactotroph subpopulations stimulated by thyrotropin-releasing hormone

Thyrotropin-releasing hormone (TRH) may stimulate lactotrophs to increase intracellular Ca(2+) and to secrete prolactin (PRL). In this study, PRL contents in lactotrophs were determined by the sequential cell immunoblot assay (SCIBA) and their changes in intracellular Ca(2+) was analyzed by confocal microscopy. Significant correlations were found in the corresponding parameters between TRH treatments with a recovery interval of 2 h. Measuring the PRL contents after the first TRH treatment and then determining the intracellular Ca(2+) changes after the second TRH treatment revealed four lactotroph subpopulations. Type I cells (51%) showed significant responses of both PRL secretion and intracellular Ca(2+) concentration. Type II cells (22%) increased in PRL secretion, but without changes in intracellular Ca(2+). Type III cells (17%) have increased in intracellular Ca(2+), but without changes in PRL secretion. Type IV cells (10%) did not show changes in PRL secretion and intracellular Ca(2+).