Thyrotropin-releasing hormone (TRH) may stimulate lactotrophs to increase intracellular Ca2þ 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 Ca2þwas 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 Ca2þ changes after the second TRH treatment revealed four
lactotroph subpopulations. Type I cells (51%) showed significant responses of both PRL secretion and intracellular Ca2þ
concentration. Type II cells (22%) increased in PRL secretion, but without changes in intracellular Ca2þ. Type III cells
(17%) have increased in intracellular Ca2þ, but without changes in PRL secretion. Type IV cells (10%) did not show
changes in PRL secretion and intracellular Ca2þ. J. Cell. Biochem. 87: 126–132, 2002.
