Proopiomelanocortin messenger RNA levels are increased in the anterior pituitary of the sheep fetus after adrenalectomy in late gestation.

We have investigated the effect of bilateral adrenalectomy at 116-119 days' gestation on the levels of the messenger (m) RNA for proopiomelanocortin (POMC) in the anterior pituitary of the fetal sheep and in the ovine placentome during late gestation (134-136 days' gestation). After fetal adrenalectomy there was a significant (p less than 0.001) and sustained increase in circulating ACTH concentrations in the adrenalectomised group (1,838 +/- 155 ng/l at 130-136 days) when compared with the intact control group (131 +/- 25 ng/l at 130-136 days). The mean levels of POMCmRNA relative to 18S RNA were also significantly higher (p less than 0.001) in the adrenalectomised fetal sheep pituitaries (2.8 +/- 0.12; n = 4) than in the intact/control fetal sheep pituitaries (1.31 +/- 0.13; n = 4). In contrast to the findings in the anterior pituitary, POMCmRNA was not detected in RNA extracted from the placentomes of either the adrenalectomised or intact fetal sheep. There was also a significant arteriovenous difference in ACTH concentrations in the umbilical circulation in both adrenalectomised and intact fetal sheep at 134-136 days' gestation. This study demonstrates therefore that the fetal adrenals act to suppress POMCmRNA levels in late gestation and also that the increase in circulating ACTH after adrenalectomy originates from the pituitary and not the placentome.