ACTH and cortisol responses to sequential CRF injections in fetal sheep.
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 response 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.
Kerr
D R
DR
Department of Physiology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina 27103.
Castro
M I
MI
Rawashdeh
N M
NM
Rose
J C
JC
D000302:Adrenal Cortex / Q000196:embryology / Q000378:metabolism; D000324:Adrenocorticotropic Hormone / Q000097:blood / Q000378:metabolism*; D000818:Animals; D002245:Carbon Dioxide / Q000097:blood; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology*; D005260:Female; D005865:Gestational Age; D006400:Hematocrit; D006854:Hydrocortisone / Q000097:blood / Q000378:metabolism*; D007700:Kinetics; D010100:Oxygen / Q000097:blood; D010313:Partial Pressure; D010902:Pituitary Gland / Q000196:embryology / Q000378:metabolism; D011247:Pregnancy; D012016:Reference Values; D012756:Sheep
D002245:Carbon Dioxide; D000324:Adrenocorticotropic Hormone; D003346:Corticotropin-Releasing Hormone; D010100:Oxygen; D006854:Hydrocortisone