AGE-RELATED HORMONAL DIFFERENCES IN CYCLING SQUIRREL-MONKEYS (SAIMIRI-BOLIVIENSIS BOLIVIENSIS)

This study was planned to evaluate the poor reproductive performance o f aged squirrel monkeys in a self-sustaining breeding colony. Two grou ps of monkeys aged 6-8 years (Group 1), and > 12 years (Group 2) were evaluated. During the midbreeding season, daily blood samples were obt ained for a period of 35 days from 10 animals in each group. Blood sam ples were assayed for serum estradiol (E), progesterone (P), and bioas sayable luteinizing hormone (bio-LH) concentrations and the data were analyzed by ANOVA (analysis of variance). Bio-LH surges were less freq uent in the aged breeders (Group 2). Total P output during periovulato ry period (day -3 to day +3) and the total P output during the luteal phases of the estrus cycles were significantly lower in aged squirrel monkeys (Group 2, P < 0.003). Although E peaks occurred less frequentl y in Group 2, they had higher concentrations as compared to Group 1 (P < 0.003). Cumulative periovulatory and luteal phase E levels did not differ between the two groups. The reduction in P output in aged squir rel monkeys may interfere with proper implantation, thus contributing to the lower pregnancy rate observed in this age group. The decreased frequency of bio-LH surges indicated less frequent ovulations in the a ged animals which may further impair reproduction with aging. (C) 1994 Wiley-Liss, Inc.