ABSTRACT
This study was planned to evaluate the poor reproductive performance of aged squirrel monkeys in a self-sustaining breeding colony. Two groups of monkeys aged 6-8 years (Group 1), and >12 years (Group 2) were evaluated. During the midbreeding season, daily blood samples were obtained for a period of 35 days from 10 animals in each group. Blood samples were assayed for serum estradiol (E), progesterone (P), and bioassayable luteinizing hormone (bio-LH) concentrations and the data were analyzed by ANOVA (analysis of variance). Bio-LH surges were less frequent in the aged breeders (Group 2). Total P output during periovulatory 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 frequently 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 squirrel 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 aged animals which may further impair reproduction with aging. © 1994 Wiley-Liss, Inc.
ABSTRACT
Studies on the reproductive mechanisms of the squirrel monkey have been hampered by inadequate measurements of luteinizing hormone (LH). The mouse interstitial cell bioassay, which measures testosterone production as the endpoint, was validated for use in the squirrel monkey by parallel responses of serum to LH standards and by in vivo responses to an LH-releasing hormone (LHRH) analogue. The LH surge profile, as determined by daily blood sampling, was found to be of 1-2 days duration and comparable in amplitude to those of other primates. A 9.7-day ovulatory cycle length was also calculated and was similar to previous estimates based on other hormonal and behavioral methods. A 150-fold decrease in basal LH was found in the nonbreeding season, as was a decreased LHRH response. This assay makes possible future studies on hypothalamic-ovarian mechanisms in this species.
ABSTRACT
Serial measurements of estradiol (E2) and progesterone (P) were used to describe the ovarian cycle of the Bolivian squirrel monkey. Group-caged, sexually mature female squirrel monkeys, housed with males, were sampled daily between 0900 and 1100 hr. Sampling was carried out during the breeding and nonbreeding seasons, for periods of 19-20 days from September 1981 to May 1982. Seasonal differences in serum concentrations of E2 and P were found with low levels of E2 and P and an absence of preovulatory surges of E2 during the nonbreeding season. This pattern was also observed in some animals during the breeding season. An abrupt increase in serum P concentrations in December appeared to signal the onset of cycling. Cycling animals had well-defined peaks of E2 (450-9,500 pg/ml) followed by increasing levels of P, which were >200 ng/ml in some animals. After the breeding season, E2 and P levels returned to their initially low levels. Levels of both steroids in cycling animals were higher than those reported for other primates and for previous measurements made in squirrel monkeys. Cycle length based on time interval between consecutive E2 peaks varied from 6-12 days.
