ACTH and cortisol responses to sequential CRF injections in fetal sheep
Kerr, D.R.; Castro, M.I.; Rawashdeh, N.M.; Rose, J.C.
American Journal of Physiology 262(3 Pt 1): E319-E324
1992
ISSN/ISBN: 0002-9513 PMID: 1312789 Document Number: 393795
To determine whether an initial ovine corticotropin-releasing factor (oCRF) injection modifies adrenocorticotropic hormone (ACTH) and cortisol responses to a second injection and to establish whether the effect changes throughout gestation, we studied chronically cannulated fetal lambs of 103-113 and 133-137 days gestation. Experimental groups underwent an injection (500 ng/kg iv) of oCRF, arterial blood sampling for 6 h, then a similar oCRF injection followed by sampling. In control studies, vehicle was the initial injection. After the first oCRF injection, plasma cortisol levels went from 1.7 .+-. 0.4 to 9.5 .+-. 5.2 (SE) ng/ml ("immature") and from 22.3 .+-. 4.9 to 52.5 .+-. 5.8 ng/ml ("mature"), remaining elevated for 6 h. In immature fetuses, the first oCRF injection did not alter the ACTH response to a second injection. Cortisol increases were reduced. In mature animals, ACTH and cortisol responses to oCRF were eliminated by prior oCRF. Thus a large increase in cortisol after oCRF in mature fetuses is associated with inhibition of the ACTH response to a second oCRF injection, whereas in immature animals a small increase in cortisol after the first oCRF injection is not.