Cortisol disrupts the ability of estradiol-17{beta} to induce the LH surge in ovariectomized ewes

Stress disrupts the pre-ovulatory luteinizing hormone (LH) surge in females but the mechanisms are unknown. We tested the hypothesis that cortisol compromises the ability of estrogen to induce a pre-ovulatory-like LH surge in ovariectomized ewes in both the breeding and non-breeding season. LH surges were induced in ovariectomized ewes by treatment with progesterone followed by a surge-inducing estradiol-17 beta (E2) stimulus using a cross-over design. The experiment was replicated in the breeding and non-breeding seasons. Cortisol reduced the incidence of LH surges irrespective of season. Cortisol increased the latency from E2 stimulus to the onset of the surge in the breeding season only, and suppressed the LH surge amplitude during both seasons (P <0.01). We conclude that cortisol can interfere with the LH surge in several ways: delay, blunt, and in extreme cases prevent the E2-induced LH surge. Furthermore, the effect of cortisol to delay the E2-induced LH surge is more pronounced in the breeding season. These results show that cortisol disrupts the positive feedback effect of E2 to trigger an LH surge and suggest the involvement of multiple mechanisms.