Response to thyrotropin-releasing hormone (TRH) of rat lactotrophs and somatotrophs deprived of hypothalamic control.

Intrasellar and ectopic lactotrophs and somatotrophs of intact and hypophysectomized rats were studied by histology, immunohistochemistry, electron microscopy and ultrastructural morphometry after 2 weeks of TRH treatment. Both ectopic lactotrophs and somatotrophs of hypophysectomized rats showed subcellular changes indicative of stimulation following TRH treatment. Ultrastructural morphometry revealed that in these ectopic lactotrophs, nuclear volume density decreased, while that of Golgi region and forming granules increased. Similar but less striking morphometric findings were noted in somatotrophs of this group and the intrasellar lactotrophs of treated nongrafted rats. Intrasellar somatotrophs showed increased nuclear volume density and reduced Golgi region volume density, following TRH administration. Ectopic lactotrophs and somatotrophs of intact animals were least responsive to treatment. These results indicate that both ectopic lactotrophs and somatotrophs of hypophysectomized rats are more sensitive to the stimulatory effects of TRH than those of intact animals.