Effects of hyperadrenal states on luteinizing hormone in cattle.

The effect of an induced hyperadrenal state on luteinizing hormone (LH) secretion and subsequent ovarian function was examined in both intact and adrenalectomized (ADRX) heifers. Treatments were begun on Day 2 or Day 16 of an estrous cycle in order to examine their effect on corpus luteum development or ovulation, respectively. In Experiment I, continuous intravenous infusion of ACTH (1.0 mg/24 h) to intact heifers decreased LH concentrations during the early phase of the cycle (Days 3-5). Treatment of ADRX heifers with hydrocortisone succinate (HS) (100 mg/24 h) did not appear to change mean LH concentrations, although da Rosa and Wagner (1981) have reported reduced plasma concentrations of progesterone at mid-cycle in these ACTH-treated intact heifers and HS-treated ADRX heifers. ACTH treatment of ADRX heifers had no effect on LH or progesterone. In the second study, there were similar frequencies of LH surges at the anticipated time of ovulation in all treatment groups. HS (100 mg/24 h) in ADRX heifers and ACTH (0.5 mg/24 h) in intact heifers was given continuously beginning on Day 16 of an estrous cycle. Although some animals in all groups exhibited LH surges, the ACTH-treated intact and HS-treated ADRX heifers failed to show a consistent subsequent increase in progesterone concentrations in plasma, suggesting a failure of luteal development. Although no difference was seen in baseline concentrations of LH, there was a greater difference between basal and overall mean LH concentrations in control groups than was observed in ACTH- or HS-treated animals. These induced hyperadrenal states resulted in depression of ovarian function as shown by decreased plasma progesterone during the luteal phase of the cycle. It is not known if other noncorticoid steroids from the adrenal cortex are necessary for a full expression of this effect.