Effects of Moderate Calorie Restriction on Ovarian Function and Decline in Rhesus Monkeys

Abstract

Calorie restriction (CR) has long been heralded as the only proven nutritional intervention for life extension. Recent data demonstrated that moderate CR also extended reproductive lifespan in female rats. The objectives of this project were to: 1) analyze general hormonal changes that occur with aging and menopause and 2) evaluate the effects (whether beneficial or detrimental) of moderate (30%) CR on ovarian function and decline in rhesus monkeys (Macaca mulatta). Hormone analyses demonstrated elevated FSH and reduced INHB in Old monkeys, prior to menstrual cycle irregularity and alterations in E2 or P4. Our data are the first demonstration of this hormonal event occurring in monkeys. Furthermore, moderate CR did not impair normal ovarian function or aging. Evaluation of three clinically available tests: day 3 FSH, the Clomiphene Citrate Challenge Test (CCCT) and the Exogenous FSH Ovarian Reserve Test (EFORT), demonstrated that CCCT is efficacious in monkeys, especially with the use of E2 and INHB. As such, CCCT is the most cost effective and best predictor of ovarian response. Responses were similar between CON and CR. Oocytes from old short-term CON and CR monkeys were collected and fertilized with spermatozoa collected from normal males. Interestingly, CR appears to prolong ovarian responsiveness to exogenous gonadotropins and improve embryonic development in vitro in old female rhesus monkeys. Microarray analysis of gene expression was conducted in luteinizing granulosa cells. A subset of responsive genes were identified that will require validation by via real time polymerase chain reaction (RT-PCR). These data will provide insight into potential mechanisms of direct action of CR on the ovary. Therefore, the results of this study have provided evidence for the utility of the rhesus monkey as a model for human menopause. Additionally, moderate CR did not impair normal reproductive function or decline. We also confirmed the efficacy of the CCCT in rhesus monkeys and recommend its use as a diagnostic tool. Finally, CR improved ovarian response to exogenous gonadotropins and has beneficial effects on oocyte quality and subsequent embryo development.