Effect of duration of infusion of stress-like concentrations of cortisol on follicular development and the preovulatory surge of LH in sheep

Stress-like levels of cortisol suppress follicular growth and development a nd block or delay the preovulatory surge of LH when cortisol is continuousl y administered during the late luteal and early follicular phases of the ov ine oestrous cycle. We postulated that cortisol infusion of shorter duratio n would have a similar effect. To test this hypothesis the oestrous cycles of mature ewes were synchronized using progestin-treated vaginal pessaries. Ewes were randomly assigned to one of four treatment groups. Animals recei ved cortisol (0.1 mg/kg/h; n=8) or vehicle alone (n=8) beginning 5 days bef ore, and continuing for 5 days after, pessary removal (PR). Additional grou ps received cortisol only during the 5 days period before (n=7), or the 5 d ays period after (n=8), PR. Continuous delivery of cortisol established sta ble serum concentrations of cortisol of 72.0+/-2.5 ng/ml within 6 h of init iation of infusion. Serum concentrations of oestradiol increased progressiv ely during the period after PR in control animals receiving vehicle alone a nd the preovulatory surge of LH was evident in all control animals (eight o f eight) 55.5+/-5.0h after PR. In contrast, follicular development and the preovulatory surge of LH were evident during the period of cortisol infusio n in only one of eight animals receiving stress-like levels of cortisol ove r the entire 10-day infusion period. Similarly, neither follicular developm ent nor surge-like secretion of LH were evident during the infusion period in animals (zero of eight) receiving cortisol during the 5-day period after PR. This cortisol-dependent suppression of ovarian activity in sheep recei ving stress-like levels of cortisol during the 5 days after PR was temporar y and follicular development, the ovulatory surge of LH, and subsequent lut eal function were evident in six of eight ewes after cessation of cortisol, delivery. Similarly, follicular development and the preovulatory surge of LH were noted within 5 days after PR in four of seven ewes receiving cortis ol only during the 5-day period prior to PR. Collectively, these data indic ate that stress-like levels of cortisol reduce fertility of sheep by suppre ssing follicular development and the preovulatory surge of LH. Additionally , cortisol delivery during the follicular phase has a more profound suppres sive effect on follicular development than cortisol administration during t he luteal phase. (C) 2000 Elsevier Science B.V. All rights reserved.