Plasma progesterone response following ACTH administration during mid-gestation in the pregnant Brahman heifer

Previous reports of adrenal progesterone (P 4) contributions during late gestation in cattle, and ACTH-induced P 4 responses in the non-pregnant heifer, prompted a retrospective investigation to evaluate the plasma P 4 response and the relative ratio of plasma cortisol (CT) to P 4 following ACTH adm...

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Bibliographic Details
Published in:Theriogenology 2005-03, Vol.63 (4), p.1061-1069
Main Authors: Willard, S.T., Lay, D.C., Friend, T.H., Neuendorff, D.A., Randel, R.D.
Format: Article
Language:English
Subjects:
ACTH
Adrenal
Adrenal Glands - physiology
Adrenocorticotropic Hormone - administration & dosage
Animals
blood plasma
Cattle
Cattle - blood
Female
Gestational Age
heifers
hormone secretion
Hydrocortisone - blood
Pregnancy
Progesterone
Progesterone - blood
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Summary:Previous reports of adrenal progesterone (P 4) contributions during late gestation in cattle, and ACTH-induced P 4 responses in the non-pregnant heifer, prompted a retrospective investigation to evaluate the plasma P 4 response and the relative ratio of plasma cortisol (CT) to P 4 following ACTH administration during mid-gestation in pregnant Brahman heifers. Twenty-three pregnant (139.0 ± 5.0 days of gestation) Brahman heifers received one of the following treatments: 0 (saline; n = 5), 0.125 ( n = 4), 0.25 ( n = 5), 0.5 ( n = 4), or 1.0 ( n = 5) IU of ACTH per kg BW. Blood samples were collected at −15 and −0.5 (time 0), 15, 30, 45, 60, 75, 105, 135, 165, 195, and 255-min post-ACTH challenge. Plasma P 4 and CT were quantified by RIA. Pre-ACTH P 4 did not differ ( P > 0.10) among ACTH treatment groups (pooled, 12.1 ± 0.6 ng/mL). Among peak P 4 values at 15-min post-ACTH infusion, control P 4 (9.6 ± 1.2 ng/mL) tended to be lower ( P < 0.07) than 0.5 IU ACTH-treated heifers (13.3 ± 1.1 ng/mL); and were lower ( P < 0.02) than 0.25 and 1.0 IU ACTH-treated heifers (14.7 ± 1.1 and 22.2 ± 3.7 ng/mL, respectively). During the primary P 4 response period (0 to 75-min post-ACTH), the area under the curve (AUC) was greater ( P < 0.05) for 1.0 IU ACTH-treated heifers than all other groups. The CT:P 4 ratios were lower (time × treatment, P < 0.01) for control heifers than all ACTH-treated heifers. Among ACTH-treated heifers, CT:P 4 ratio response and CT:P 4 ratio AUC were similar ( P > 0.10) following ACTH challenge. In conclusion, acute increases in ACTH elevated plasma P 4, likely of adrenal origin, in mid-gestation pregnant heifers, while the CT:P 4 ratio (relative output) remained constant irrespective of ACTH dose (0.125–1.0 IU). Whether ACTH-induced increases in P 4 in pregnant animals are of physiological significance (e.g., an accessory role in the maintenance of pregnancy during periods of acute stress) remains to be determined.
ISSN:0093-691X
1879-3231
DOI:10.1016/j.theriogenology.2004.05.018