The benefits of calorie restriction (CR) have been established across a variety of vertebrate and invertebrate species. Although the effects of CR on lifespan in birds have not been examined, it is clear that CR has beneficial effects on reproductive, metabolic, and physiological function in adult poultry. We examined the effects of CR in Japanese quail, a rapidly maturing avian model, on reproductive endocrine and neuroendocrine systems. Male Japanese quail were pair fed at 0% ad libitum (AL), 20%, or 40% CR of AL, recorded for juveniles (3-7 weeks of age) or adults (12-16 weeks of age). Juvenile males on CR matured more slowly, and both juvenile and adult males had reduced plasma luteinizing hormone (LH) with CR. Adults on 40% CR showed evidence of stress, with increased plasma corticosterone and reduced testes weight and circulating androgens. In a separate study, pituitary gland response was tested in juvenile and adult castrated males that had been on the same CR treatments. All birds responded to gonadotropin releasing hormone (GnRH) challenge, with LH release. However, the 40% CR juvenile and adult birds had quantitatively lower responses, suggesting central inhibition of the reproductive axis. This hypothesis was tested by measurement of sexual behavior and catecholamines known to stimulate GnRH in hypothalamic regions that modulate these responses. Results showed reduced norepinephrine in key hypothalamic regions and reduced dopamine in posterior hypothalamus. These data support the hypothesis that CR affects reproductive function, with evidence for effects in the central nervous system. These data are discussed and compared to data collected in mammals, especially the rhesus monkey, on the effects of timing and degree of CR on reproductive and stress responses.

Restricting food intake to 60% that of ad libitum-fed rats results in an extended life span, reduced incidence of age-related diseases, and delayed reproductive senescence. We used this animal model to further elucidate the mechanisms whereby reproductive senescence is delayed. Female Sprague-Dawley rats (7 wk old) were calorically restricted (CR; n = 70) to 60% of the ad libitum(AL) intake measured in control rats (n = 70). Rats were individually housed under a 14L:10D cycle and fed daily within 1.5 h of lights-off. Body weights were monitored every 2 wk, and vaginal lavage was performed until rats were ovariectomized (OVX). Two weeks after OVX, when rats were 4, 12, or 18 mo of age, blood samples were taken via jugular cannulae every 6 min for 3 h, and the plasma was assayed for rat LH. The resulting profiles were examined through use of Cluster analysis for mean LH concentrations, LH pulse amplitude, and interval between LH pulses. CR rats grew at a slower rate, and then maintained body weights at approximately 76% that of AL controls between 4 and 17.5 mo of age. The onset of persistent estrus was delayed by 4 mo in CR rats. Average cycle length was longer (p < 0.01) by less than 0.5 days in CR compared with AL rats between 3.5 and 5.5 mo of age but not different between 6.5 and 11.5 mo. Mean levels of LH in OVX rats decreased with age (p < 0.01), increased with caloric restriction (p < 0.05), and decreased with declining cycling status of the animal prior to OVX (regular [reg] vs. irregular [ir] vs. persistent estrus [pe]; p < 0.05). The increased mean LH due to caloric restriction was attributed to an increase in mean pulse amplitude and not to a decrease in time interval between LH pulses. From these data we conclude that the beneficial effects of caloric restriction on reproductive longevity may be acting at the level of the hypothalamus and/or pituitary to enhance LH secretion and do not require a delay in puberty or a period of acyclicity.

Reproductive ageing in female rodents is accompanied by changes in circulating peptide and steroid hormones leading to irregular, lengthened oestrous cycles prior to loss of fertility. In this study, the effect of ageing is reported on steroid hormone synthesis within individual ovarian follicles and its retardation by restricted feeding for two groups of ad libitum fed animals (114 and 350 days) and two groups of diet-restricted animals (350 and 600 days). Follicles from ad libitum fed animals of 350 days showed a transition in follicular steroid hormone synthesis to release elevated amounts of oestradiol-17beta on all days of the cycle. This age-related change in follicle steroid release was significantly delayed by maintaining animals on a restricted feeding regime, and was not complete even by 600 days of age. This effect of diet as a means to manipulate ageing of the follicular steroidogenic pathways provides a useful system for investigating the control of reproductive ageing in rodents.