Effect of bilateral splanchnic nerve section on adrenal function in the ovine fetus

The effect of bilateral splanchnic nerve (SPLX) section in fetal sheep [116-121 days gestational age (dGA)] on subsequent adrenocortical function was investigated. Fetal cortisol release was stimulated by 1) ACTH-(1-24) administration (100 ng/min for 15 min) at 126-129 and at 132-135 dGA, and 2) nitroprusside-induced hypotension (50% reduction in fetal arterial blood pressure for 10 min) at 129-132 and 136-139 dGA. No differences were observed between SPLX and control fetuses (CONT) in basal arterial plasma concentrations of cortisol from 126-141 dGA. A significant effect of fetal age on basal cortisol was observed in both SPLX and CONT fetuses from 126-141 dGA. A significant (P less than or equal to 0.05) increase in fetal arterial concentrations of cortisol was achieved by ACTH-(1-24) infusion in SPLX and CONT and did not differ between groups at either 126-129 or 132-135 dGA. Hypotension induced a significant increase in fetal plasma cortisol concentrations in SPLX and CONT fetuses (P less than or equal to 0.05). SPLX fetuses secreted significantly less cortisol in response to hypotension than CONT fetuses at both 129-132 and 136-139 dGA (P less than 0.05). Fetal arterial plasma concentrations of immunoreactive ACTH in response to hypotension were not different between CONT and SPLX fetuses. We estimated the half-life of endogenous fetal plasma cortisol after both hypotension and infusion of ACTH-(1-24). There were no differences between either method of inducing cortisol release on the endogenous cortisol half-life, nor were any differences in cortisol half-life observed between SPLX and CONT. At 136-139 dGA the adrenomedullary response to hypotension was abolished in SPLX, confirming completeness of denervation. In conclusion, the splanchnic nerves do not appear to be involved in the normal increase in basal fetal plasma cortisol observed in late gestation in fetal sheep. However, splanchnic nerve modulation of secretion of cortisol in response to stress may be involved in the increased fetal adrenal sensitivity to stress observed late in gestation.