Action of thyrotropin-releasing hormone on mammotrophs and thyrotrophs

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Abstract
Anterior pituitary cells from 15-day-old female rats were separated by unit gravity sedimentation into 4 populations (designated regions I-IV) based on the profile of cell distribution and the resulting content of radioimmunoassayable (RIA) hormones. The cells in regions II and IV released TSH in response to (TRH , 5 ng/ml); those in region IV released only .apprx. 5% of their RIA content, whereas those in region II released .apprx. 26% in response to the same stimulus. Concomitant elevation of cAMP and of cGMP occurred in region II cells but only cGMP was elevated in region IV cells. Mammotrophs were localized in region III. They responded to TRH by releasing prolactin (PRL) and exhibiting increased cAMP content. These data provide support for the existence of 2 functionally distinct populations of thyrotrophs in 15-day-old female rats. The data also imply that cAMP is involved in TRH-induced PRL release; cGMP is involved in TRH-induced TSH release.