Changes in lactotroph responsiveness to secretagogues as determined by the sequential cell immunoblot assay

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We investigated heterogeneity for the responsiveness of lactotrophs to secretagogues and the effects of estradiol on the responsiveness by quantifying prolactin secretion at the single cell level.1. Heterogeneity for the responsiveness of lactotrophs to thyrotropin-releasing hormone(TRH)(1) Although prolactin secretion from single lactotrophs in culture was increased by TRH in a dose-dependent manner, approximately 50% of total lactotrophs were not stimulated by TRH even at a maximally effective dose. This result suggests that there are two subpopulations of lactotrophs that are responsive and unresponsive to TRH.(2) A population of lactotrophs that secrete small amounts of prolactin under basal conditions contains a much larger proportion of TRH-responsive lactotrophs than does a population of lactotrophs that secrete large amounts of prolactin.2. Changes by estradio1 in the responsiveness of lactotrophs to secretagogues(1) When the effects of estradiol treatment on prolactin secretion from a population of lactotrophs to medium were examined, it was found that estradiol increased basal secretion of prolactin. Estradiol attenuated and enhanced the inhibitory action of dopamine and the stimulatory action of TRH, respectively, on prolactin secretion.