Periovulatory Endocrine Events in the Stumptailed Monkey (Macaca arctoides)*

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Abstract
Blood samples were obtained frequently from stumptailed monkeys (Macaca arctoides) at midcycle and assayed for FSH, LH, 17β-estradiol, and progesterone. Periovulatory endocrine events were generally similar to those which have been described in rhesus monkeys and women. Although the midcycle patterns of estradiol in individual monkeys appeared quite varied, careful evaluation indicated the following general characteristics: 1) a plateau or transient decline in estradiol 30– 44 h before the LH peak, 2) a sharp rise in serum estradiol before the initiation of the LH rise, 3) a diminution in serum concentrations or a decline in the rate of estradiol increase at the initiation of the LH rise, and 4) an elevation in estradiol at the time of the highest serum LH value. The first elevation in serum progesterone occurred 0–12 h before the LH peak and after the initiation of the LH surge. An unusual finding was a second midcycle rise in serum FSH, which occurred 2–3 days after the LH peak in 10 of 13 menstrual cycles. The biological significance of this second FSH rise in stumptailed monkeys is not known with certainty, but available evidence suggests that it enhances postovulatory progesterone and estrogen syntheses. Two methods are presented for the RIA of serum FSH in the stumptailed macaque.