Follicle dominance and ovarian asymmetry after luteectomy in rhesus monkeys

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Abstract
Previous work demonstrated that asymmetrical ovarian activity accompanies morphological asymmetry during the ovarian cycle in rhesus and cynomolgus macaques. This study was designed to determine whether functional ovarian asymmetry could be used to detect the upcoming dominant follicle (DF) even before it was grossly visible. Revealing a latent DF in this manner would permit a better estimate of the time when dominance of the follicle selected to ovulate is attained. To accomplish this, rhesus monkeys were luteectomized at midluteal phase to synchronize subsequent follicle growth, and 4 or 8 days later either the ipsilateral or contralateral ovary was removed. Unilateral ablation at day 4 (when no DF is grossly apparent) of either ovary produced symmetrical responses: the interval from luteectomy (CLX) to the next luteinizing hormone (LH) surge was extended by about 4 days in both groups (P less than 0.01), i.e., from about 12.5 days to 16.7 +/- 1.6 and 17.0 +/- 1.5 days (mean +/- SE). In contrast, hemiovariectomy at day 8 produced markedly divergent asymmetrical responses. Removal of the ipsilateral ovary 8 days after CLX did not affect the timing of the next LH surge (13.2 +/- 0.6 days), which ordinarily occurs about 12.5 days after CLX alone. However, ablation of the contralateral ovary (bearing the next DF) on day 8 extended the interval from CLX to the next LH surge from about 12.5 to 26.6 +/- 1.3 days. These findings indicate that, during the normal ovarian cycle when menses occurs 2--4 days after luteolysis, the follicle destined to ovulate becomes dominant between the 2nd and 6th day and that attainment of dominance signals the completion of a follicle selection process that begins or resumes promptly after luteolysis.

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