Features of female reproductive senescence in tamarins (Saguinus spp.), a New World primate.

Cyclical changes in concentration of plasma progesterone, urinary oestrone-conjugates and urinary luteinizing hormone (LH) were compared in young and older cotton-top tamarins (Saguinus oedipus) and saddle-backed tamarins (S. fuscicollis). A group of six young adult tamarin females (4-5 years of age) was sampled over eight periods of 6-8 weeks and six older (14-20 years of age) females were sampled over thirteen periods. There was hormonal evidence of ovulation in all of the sampling periods for young females; in five of thirteen periods, older females displayed no evidence of ovulation. Of the six older females, two were anovulatory in one sampling period, while one female displayed no evidence of ovulation in any of three sampling periods. Generally, females over 17 years of age either did not ovulate or displayed abnormally long periods of moderate concentrations of progesterone and oestrone conjugates. Basal concentrations of LH differed in individuals, but were not always higher in older females. In contrast to patterns of reproductive senescence in other primates, older, anovulatory tamarins displayed moderate concentrations of urinary oestrone conjugates (5-50 micrograms/mg creatinine) and plasma progesterone (8-19 ng/ml), both of which are hormones of probable luteal origin in these species. This result suggests continued production of steroids by the luteal cells of the prominent interstitial gland in reproductively senescent tamarins. This suggestion was reinforced by histological examination of the ovaries of four older, anovulatory females; few primary follicles were found. Three females had no normal antral follicles, but all females had large luteal masses. The presence of functional luteal cells in the older ovaries, which do not experience regular follicular development, may distinguish ovarian ageing in New World primates from that of Old World primates.