Prolonged absence of ovarian hormones in the ewe reduces the adrenocorticotropin response to hypotension, but not to hypoglycemia or corticotropin-releasing factors

Abstract

The ACTH responses to hypotension, hypoglycemia, CRF, arginine vasopressin (AVP), and the combination of CRF and AVP were compared to determine whether there was a general decrease in ACTH responses to these stimuli in ovariectomized ewes compared to intact animals. The ovariectomized ewes were studied either 2-4 weeks post-ovariectomy (acute) or 4-7 months post-ovariectomy (chronic). Each ewe was subjected to saline control infusion, nitroprusside-induced hypotension (100 micrograms/min for 10 min), insulin-induced hypoglycemia (25 U porcine insulin), CRF (1 microgram/min for 60 min), AVP (0.2 microgram/min), and a combination of CRF plus AVP. In each experiment, plasma ACTH concentrations were measured at 10-min intervals for 1 h. The peak ACTH concentrations were significantly lower in response to hypotension in the chronic ewes compared to those in either the intact or acute group. The ACTH response to hypoglycemia was not significantly reduced in either ovariectomized group. The ACTH responses to CRF, AVP, and the combination of both were not significantly reduced in either ovariectomized group. The results suggest that the effect of ovariectomy on the ACTH response to stress occurs at a site within the brain and does not involve altered pituitary responsiveness to CRF or AVP.