Rate of decline of cortisol concentrations in ovarian follicles following ACTH treatment in the sow.

The rates of decline in cortisol concentrations in blood and ovarian follicular fluid were assessed in cyclic sows (n = 30) after treatment with saline or a depot form of adrenocorticotrophic hormone (ACTH). After a single injection of ACTH (0.5 iu/kg, BW, i.m.), peak cortisol values were achieved in blood within 3 to 4 h followed by a half-life net clearance rate (t1/2 of 2.40 +/- 0.29 (SE) h. The same dose of ACTH was then given at 12 h intervals from days 9 to 13 of the estrous cycle. On day 14 the concentrations of cortisol in follicular fluid were higher (P < 0.05) in ACTH-injected sows than in saline-injected controls. A t1/2 value of 37.81 h was determined for cortisol based on the decline in concentrations in follicular fluid collected on days 14, 16 and 18. This relatively slow rate of removal from developing ovarian follicles may have implications for the previously observed detrimental effects of increased cortisol concentrations on follicular development.