Ontogeny of proopiomelanocortin posttranslational processing in the ovine fetal pituitary.

In the sheep, parturition is stimulated by increased hypothalamus-pituitary-adrenal axis activity in the fetus. Factors influencing the storage and processing of adrenocorticotropic hormone (ACTH) secretion in the fetal pituitary is therefore important in this process. We hypothesized that the pituitary content of ACTH, particularly ACTH(1-39), increased with developmental age. Fetal pituitaries were collected from healthy animals (74 days gestation to 4 weeks postnatally) and analyzed by radioimmunoassay and Western blot. Pituitary content of immunoreactive ACTH(IR-ACTH) increased significantly with developmental age (p < 0.05). As measured by Western blot analysis, the proportion of ACTH(1-39) to POMC and pro-ACTH (22 kDa) also increased significantly with developmental age. We also examined the effect of exogenous estrogen and androgen treatment on pituitary ACTH. Pituitary content of IR-ACTH was not different from controls but the proportion of ACTH that was present as ACTH(1-39) decreased with the estradiol treatment. In conclusion, IR-ACTH content increases in the fetal sheep as does the proportion of ACTH (1-39) relative to POMC and the 22-kDa fragment developmentally.