ONTOGENY OF PROOPIOMELANOCORTIN POSTTRANSLATIONAL PROCESSING IN THE OVINE FETAL PITUITARY

In the sheep, parturition is stimulated by increased hypothalamus-pitu itary-adrenal axis activity in the fetus. Factors influencing the stor age and processing of adrenocorticotropic hormone (ACTH) secretion in the fetal pituitary is therefore important in this process. We hypothe sized that the pituitary content of ACTH, particularly ACTH(1-39), inc reased with developmental age. Fetal pituitaries were collected from h ealthy animals (74 days gestation to 4 weeks postnatally) and analyzed by radioimmunoassay and Western blot. Pituitary content of immunoreac tive 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 a nd androgen treatment on pituitary ACTH. Pituitary content of IR-ACTH was not different from controls but the proportion of ACTH that was pr esent as ACTH(1-39) decreased with the estradiol treatment. In conclus ion, IR-ACTH content increases in the fetal sheep as does the proporti on of ACTH(1-39) relative to POMC and the 22-kDa fragment developmenta lly.