Developmental Expression of Bovine Adrenocortical Steroid Hydroxylases

The developmental expression of adrenocortical steroid hydroxylases was studied in bovine fetuses from 40 to 280 days gestational age. The expression of P45017, is first detected at a gestational age of 50 days and reaches a maximum at 60-70 days. The expression of P-45017, then declines and is nondetectable at a gestational age of 100 days. P-45017, is not expressed again until about 240 days, Le. shortly before birth (-280 days). P-450,, P-450c21, P-450116 and adrenodoxin were present in fetal adrenals throughout gestation. This “on-off-on” pattern of P-45017, expression during fetal development was associated with a corresponding episodic production of cortisol. Immunoreactive corticotropin (ACTH) levels in fetal plasma were elevated in small fetuses (corresponding to 5100 days) and in near-term fetuses (corresponding to >250 days) compared with those in mid-gestation fetuses. In primary culture, adrenal cells from mid-gestation fetuses contained no detectable P-45017, but rapidly responded to ACTH with an increase in P-45017, protein and mRNA. The tissue specificity of the developmental patterns is emphasized by the fact that both P-45017, and P-460, were detectable throughout the development of the fetal testes, whereas only P-450,, was detectable in fetal bovine ovary prior to 200 days. Thus, in fetal bovine adrenal it appears that ACTH is the major regulatory factor effecting the intermittent presence of P-45017,, whereas the presence of the other steroid hydroxylases is either regulated by additional factors or shows a much different sensitivity to ACTH.