AJP - Endocrinology and Metabolism, Vol 265, Issue 1 E68-E73, Copyright © 1993 by American Physiological Society

ARTICLES

Bioactive-to-immunoreactive ACTH activity changes with severity of stress in late-gestation ovine fetus

M. I. Castro, N. K. Valego, T. J. Zehnder and J. C. Rose
Department of Obstetrics and Gynecology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina 27157-1066.

The late-gestation ovine fetus (> 130 days, 0.90 gestation, full term 145 days) is capable of increased pituitary-adrenal activity following a variety of stressors. To examine the relationship between plasma immunoreactive adrenocorticotropic hormone (iACTH) and bioactive ACTH-like activity (bACTH), late-gestation fetuses were studied under nonstress (group I, chronically catheterized), "mild" stress (group II, acutely exteriorized), or marked stress (group III, acutely exteriorized and hemorrhaged 30% of blood volume). Plasma iACTH was determined by standard radioimmunoassay. Plasma bACTH was determined by a bioassay that utilized dispersed rat adrenal cells. Plasma iACTH was lower in group I than in groups II or III (78.4 +/- 16.3 vs. 320 +/- 116 and 622 +/- 144 pg/ml, respectively, mean +/- SE, P < 0.05 group I vs. III). Plasma bACTH was significantly lower in groups I and II than in group III (13.8 +/- 2.7 and 52 +/- 22 vs. 601 +/- 106 pg/ml, respectively, P < 0.05). The ratio of bACTH to iACTH was low in groups I and II but elevated in group III (0.188 +/- 0.028 and 0.091 +/- 0.07 vs. 0.996 +/- 0.122, P < 0.05). We conclude that the amount of bACTH compared with iACTH in the late-gestation fetus is low under nonstress states or mild stress and that bACTH increases disproportionately compared with iACTH after marked stress. This suggests that a change in ACTH processing and/or secretion is associated with stimulus intensity in the late-gestation ovine fetus.

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