Adrenocorticotropin Alteration of Bovine Peripheral Plasma Concentrations of Cortisol, Corticosterone, and Progesterone,

Seven Holstein cows, 60 to 90 days postpartum, received either 200 IU ACTH (n=4) or saline (n----3) intravenously with treatments reversed 2 days later. Blood samples (30 ml) were collected fi'om indwelling jugular catheters at --60, 0 pre-injection, and 5, Solvent extraction, purification by Sephadex LH-20 column chomatography and competitive protein-binding analyses were used to isolate and quantify plasma cortisol, corticosterone, and progesterone. Mean cortisol (ng/ml) at the respective sampling times was 3.1 vs. 3.6 (saline vs. ACTH), 4.9 vs. 4.1, 5.9 vs. 33.7, 8.8 vs. 30.0, 4.8 vs. 45.8, 3.3 vs. 28.8, 3.2 vs. 31.3, 4.4 vs, 36.6, 2.6 vs. 26.8 and 5.2 vs. 34.7. Both the magnitude of the cortisol response and the interval to maximum response to ACTH varied among cows (P<.01). Adrenocorticotropin elicited a cortieosterone increase (P<.01) concurrently with the cortisol increase, but it was of lower magnitude, reaching 7.6 ng/ml at 30 rnin. Mean progesterone at the respective times was 1.7 vs. 2. 1, 2.4 vs. 2.0, 2.0 vs. 3.1, 2.0 vs. 4.5, 2.2 vs. 4.2, 2.5 vs. 4.2, 2.2 vs. 3.9, 2.3 vs. 2.4, 2.6 vs. 2.8 and 2.2 vs. 2.0 ng/ml, and the increase due to ACTH administration was significant (P<.025) between 15 to 60 rain post-injection. Results suggest that the adrenal contributes a significant proportion of plasma progesterone.