Differential response of amphibian PRL and TSH pituitary cells to in vitro TRH treatment.

Hypophysial prolactin (PRL) and thyrotropin (TSH) cells of Rana perezi were examined after treatment in vitro with synthetic thyrotropin-releasing hormone (TRH). Ultrastructural morphometry applied to PRL and TSH immunoidentified cells estimated the volume density (Vv) of the secretory granules (SG), rough endoplasmic reticulum (ER), and Golgi complex (GC) as well as the numerical density (Nv) of the granules. Hemipituitaries were cultured in a superfusion system with or without 100 ng TRH/ml for 4, 14, or 24 hr. PRL cells showed significant degranulation (42%) of medium size SG after 14 hr of stimulation, whereas the biosynthetic machinery (ER and GC) was significantly developed after 4 hr of TRH culture (increase of Vv of GC, 1.5-fold, and ER, 1.3-fold, in comparison to the control). Most of these changes remained after 24 hr of TRH treatment. Compared with controls, TRH-treated TSH cells differed only after 24 hr when SG showed degranulation (40%), mainly of the medium size ones, and Vv of GC (1.6-fold) and ER (1.3-fold) increased. These results suggest that TRH acts directly on amphibian PRL and TSH cells stimulating hormonal synthesis and release. The time courses of responses to TRH differed in that PRL cells gave an immediate response while TSH cells gave a more delayed reaction.