Serum and urinary concentrations of sex hormones and genital swelling during the menstrual cycle of the gibbon.

The relationship between sex hormone concentrations and female genital swelling during the menstrual cycle in the monogamous gibbon was comparable with that of polygamous female primates, such as the chimpanzee, which live in multimale groups and have larger swellings. The data, therefore, support the hypothesis proposed by C. R. Carpenter more than 50 years ago, that the gibbon's genital swelling, like that of other female primates, reflects basic physiological processes associated with progress of the menstrual cycle. Genital swelling increased during the follicular phase with increasing concentrations of oestradiol and oestrone glucuronide, reached maximal swelling in association with the mid-cycle peaks in the oestrogens and LH and began detumescence with the initial increases in progesterone during the luteal phase. The data also suggest that the menstrual cycle of the gibbon is shorter than previously reported, since cycles of 19-22 days exhibited hormone patterns that are consistent with ovulation. The genital swelling of the female gibbon is a useful marker for monitoring progress of the menstrual cycle and the presumptive time of ovulation.