The effect of adrenocorticotropic hormone infusion on subsequent pituitary response in the sheep fetus.

It is not known whether activation of the fetal adrenal gland can inhibit pituitary adrenal responses to stress. Therefore we treated 14 chronically cannulated sheep fetuses (gestational age range, 109 to 129 days) with an adrenocorticotropic hormone infusion of 5 ng/kg per minute or vehicle solution at similar rates for 2.5 hours and then subjected them to a 10-minute period of hypotension. Resting mean arterial blood pressures were similar for both control and adrenocorticotropic hormone infusion groups and decreased similarly after administration of sodium nitroprusside. Resting fetal plasma cortisol levels (11.6 +/- 3.3 ng/ml) and adrenocorticotropic hormone (42 +/- 15 pg/ml) concentrations were not different in the two groups. In the control group fetal plasma cortisol concentrations rose from 12.1 +/- 1.7 to 35.7 +/- 8.0 ng/ml after hypotension (p less than 0.05) and plasma adrenocorticotropic hormone increased from 37 +/- 19 to 145 +/- 67 pg/ml (p less than 0.05). In the group treated with adrenocorticotropic hormone, fetal plasma cortisol concentrations increased (30.2 +/- 7.8 to 53.6 +/- 15.0 ng/ml; p less than 0.05) after hypotension whereas fetal plasma adrenocorticotropic hormone concentrations did not increase (398 +/- 227 versus 258 +/- 77 pg/ml; p greater than 0.05).