Effects of ovine CRF on amphibian pituitary ACTH and TSH cells in vivo: a quantitative ultrastructural study.

The subcellular responses of amphibian adrenocorticotropic (ACTH) and thyrotropic (TSH) pituitary cells to the in vivo administration of ovine corticotropin-releasing factor was investigated. For this purpose, groups of six Rana perezi adult frog (three males and three females) were given daily injections of ovine CRF and sacrificed at 6 hr, 24 hr, and 4 days after the first injection. Immunogold staining, applied to ultrathin sections using antisera to human ACTH (1-39) and human beta-TSH identified ACTH and TSH cells, respectively. Morphometry was used to evaluate the volume density (Vv) changes of the rough endoplasmic reticulum, Golgi complex, and secretory granules and the numerical density of the latter. CRF significantly reduced the Vv of the secretory granules in both cell types, taken as indicative of short-term enhanced hormonal release. The peptide also stimulated the development of the cellular biosynthetic machinery, although this effect was detected at an earlier stage in ACTH cells than in TSH cells. These results show for the first time the occurrence of cellular response of amphibian adrenocorticotropes and thyrotropes to CRF and suggesting that this peptide regulates ACTH and TSH production. Moreover, each type of cell differed in its sensitivity to the peptide. After long-term treatment the cytological response of ACTH cells to CRF seemed to decrease, while TSH cells remained active.