Vasodilator response to exogenous adrenocorticotropic hormone in fetal adrenal cortex precedes increased steroidogenesis in sheep at 105–112 days gestation

Objective: To examine whether the increase in adrenal cortical blood flow induced by adrenocorticotropic hormone (ACTH) is linked to steroidogenesis, or if these effects can be separated. Study design: Adrenal cortical responses to ACTH were measured in ovine fetuses at 105–112 days gestation, when the adrenal is hyporesponsive. Fetuses were given an intravenous infusion of ACTH 1–24 or of vehicle. We measured regional adrenal blood flows by the microsphere technique and plasma ACTH and cortisol levels by radioimmunoassay. Results: After 3 and 24 h of ACTH infusion, plasma cortisol concentrations had risen from 2.8±0.8 ng/ml to 8.4±0.3 and 78.0±15.8 ng/ml (means±S.E.M.). Adrenal cortical blood flow increased from 108±25 ml/min/100 g to 319±33 and 518±51 ml/min/100 g. Plasma cortisol levels and adrenal blood flow did not change in control fetuses. Conclusion: Since there was a rapid blood flow response to ACTH, despite the expected delay in the rise of plasma cortisol, we suggest that vascular responses to ACTH are not tightly linked to adrenal metabolic activity in the ovine fetus at 0.7 gestation.