The effect of age on reproduction in repeatedly mated female rats

Obesity accelerates ovarian follicle development and follicle loss in rats

OBJECTIVE

Studies have shown that excess body fat negatively affects reproductive functions in females. However, whether obesity affects the ovarian follicle development and ovarian lifespan and the underlying mechanism has not been well elucidated. The aim of the present study was to investigate the association between obesity and ovarian follicle development.

METHODS

Adult female Sprague-Dawley rats (n = 36) were randomly divided into three groups: the normal control (NC) group, the caloric restriction (CR) group (fed 70% food of the NC group) and the high-fat diet (HF) group. They were maintained on these regimens for 18 weeks.

RESULTS

The body weight, ovary weight and visceral fat in the HF group were significantly higher than those in the NC group and the CR group at the end of treatment. Histological analysis showed that the HF rats had significantly less number and percentage of primordial follicles, but greater number and percentage of developing and atretic follicles than the NC rats and CR rats. Western blot analysis demonstrated that the level of mTORC1 and p-S6K1 proteins significantly increased in the ovaries of HF rats, whereas that of SIRT1, SIRT6, FOXO3a and NRF-1 decreased compared to the NC rats. In contrast, the expression of mTORC1 and p-S6K1 dramatically declined, while that of SIRT1, SIRT6, FOXO3a and NRF1 increased in the ovaries of CR rats.

CONCLUSIONS

Our study suggests that the HF diet induced obesity may accelerate the ovarian follicle development and rate of follicle loss through activating mTOR and suppressing SIRT1 signaling, thus leading to POF, and that CR may inhibit the activation of primordial follicles, follicular development and loss, thus extending the ovarian lifespan through suppressing mTOR and activating SIRT1 signaling.

Determinants of uterine aging: lessons from rodent models

The uterus is an indispensable organ for the development of a new life in eutherian mammals. The female mammalian reproductive capacity diminishes with age. In this respect, the senescence of uterine endometrium is convinced to contribute to this failure. This review focuses on the physiological function of the uterus and the related influence of aging mainly in rodent models. A better understanding of the underlying mechanisms governing the process of uterine aging is hoped to generate new strategies to prolong the reproductive lifespan in humans.

Effects of Nanpao, a Kampo medicine, on the decline in estrous cyclicity with advancing age in female rats, as measured by vaginal impedance methods

The present study was designed to evaluate the time-dependent effects of Nanpao, a kampo medicine, on age-related changes in the estrous cycle of female rats, and to investigate the utility of measuring electrical impedance in the vagina (EIV) for studying transitional changes in the estrous cycle. Rats were allocated to 3 groups: control, Nanpao 30 mg/kg/day, and 100 mg/kg/day groups. EIV measurements and cytology samples were taken for 14 days at the age of 6 months before the initial treatment. After the start of the treatment, these data were collected at about monthly intervals until the age of 10 months in the same manner. Observations at the ages of 7 (weeks 2-3 of dosing) and 8 months (weeks 6-7 of dosing) showed that loss of a regular estrous cycle in the 100 mg/kg/day group was inhibited as compared to the control group. Moreover, at the ages of 9 (weeks 11-12 of dosing) and 10 months (weeks 17-18 of dosing), these effects were identified not only in the 100 mg/kg/day group, but also in the 30 mg/kg/day group. Since vaginal cytology and EIV gave almost concordant results as indicators of estrous cyclicity, we concluded that the measurement of EIV was capable of detecting time-dependent changes in the estrous cycle as well as observations of vaginal smears. A short period of Nanpao administration inhibited loss of regular estrous cycles, and the EIV method is a worthwhile approach to a more precise study of estrous cyclicity in rats exhibiting abnormal estrous cycles.

Anti-aging effects of nanpao, a kampo medicine, on reproductive functions in female rats

The improvement effect of nanpao, a kampo medicine, on the age-related decline in reproductive function was evaluated in female rats given the test drug for a long-term period. Young rats were allocated to the cesarean section and natural delivery groups to examine reproductive performance (young rat groups). Five-month-old rats were allocated to the 3 groups (aged rat groups): 1--control and 2--nanpao-treated groups. They were given orally in a dose of 0, 30 or 100mg/kg/day of the test drug, respectively. In aged rats, the first mating experiment was initiated at week 21 of dosing to evaluate reproductive performance by natural delivery and the second mating experiment at week 31 of dosing was evaluated by cesarean section. In the first and second mating experiments, various reproductive functions decreased in aged rats as compared to the young rats. On the other hand, loss of regular estrous cycles, decreases in delivery and pregnancy rates and mean fetal weights were inhibited in the treated groups as compared to the control group. In addition, decreases in the numbers of mean live offspring and fetuses were inhibited in the 100 mg/kg/day group. In conclusion, nanpao maintained normal embryo-foetal development in female rats.

Influences of age and ovarian follicular reserve on estrous cycle patterns, ovulation, and hormone secretion in the Long-Evans rat

This study examined the influences of aging and reduced ovarian follicular reserve on estrous cyclicity, estradiol (E(2)) production, and gonadotropin secretion. Young virgin and middle-aged (MA) retired breeder female rats were unilaterally ovariectomized (ULO) or sham operated (control). Unilateral ovariectomy of young rats reduced the ovarian follicular reserve by one-half, to a level similar to that found in MA controls. Unilateral ovariectomy of MA females reduced the follicular pool further, to one half of MA controls. The incidence of regular cyclicity was significantly lower in MA ULO females than in young controls, with intermediate cycle frequency in young ULO and MA controls. Among cyclic rats, the magnitude of the proestrous LH surge was highest in young controls, intermediate in young ULO rats and MA controls, and lowest in MA ULO females. Similarly, ovulation rates were highest in young controls, intermediate in young ULO rats and MA controls, and lowest in MA ULO females. While young ULO rats exhibited augmented secondary FSH surges on estrous morning, middle-aged ULO females displayed secondary FSH levels comparable to young controls. The effects of age and reduced follicle number on estrous cyclicity and gonadotropin secretion were not due to altered E(2) secretion, as preovulatory E(2) levels were similar among all groups. Thus, experimental reduction in the follicular reserve exerts acute effects on the preovulatory LH surge, ovulation rate, and estrous cyclicity in both young and MA rats. However, decreased follicle number increases FSH levels only in young rats, indicating aging-related alterations in the feedback regulation of FSH.

Characteristics of uterine aging

Uterine aging is in part responsible for a decline in fecundity which begins in middle age in most mammals. Characteristics of uteri from a variety of animals in middle age and old age are reviewed and the factors which may be responsible for this decline discussed. These include age-related changes in the hypothalamus, pituitary, and ovaries; loss of number or function of steroid hormone receptors; morphological changes in the uterine epithelium; the accumulation of collagen fibrils in the uterine stroma; and loss or impairment of the decidual response. The ultrastructural morphology of uterine epithelial, stromal, and decidual tissue from 4 month old and 18 month old Fischer 344 rats is presented and compared.

Age-related reproductive decline in the male Japanese quail

A series of experiments was conducted to study the decline in reproduction associated with age in the male Japanese quail. In Experiment 1, eggs were collected from pairs that were 28, 56, 107, and 149 weeks of age. Pairs that were 56 weeks of age or older showed a sharp drop in fertility and hatchability. Subsequent experiments were designed to study the endocrine and behavioral basis for this decline in the male. In Experiment 2, males that were between 23 and 70 weeks of age were tested for mating behavior, plasma testosterone was measured, and testes wet weight was determined. There were no significant differences between the age groups. However, samples taken from an additional group of males 168 weeks of age showed significantly (P less than 0.05) lower serum testosterone and testes weight. Therefore, the third experiment was designed to include age groups of males between 4 and 126 weeks of age in order to further examine this decline in males older than 70 weeks of age. There was a significant (P less than 0.05) drop in this number of males showing sexual behavior and of those males showing sexual behavior; the quantity of mating activity also declined. Plasma testosterone was reduced in the older groups; however, the change was not significant. In addition, the size of the cloacal gland, an androgen-dependent organ, declined with age (P less than 0.05). These results argue that the age-related reproductive decline may have behavioral as well as endocrine basis. Possibly, the behavioral changes may result from altered receptor sensitivity at the level of areas of the brain, which control reproductive behavior, and at the level of the testes, which affect hormone production and spermatogenesis.

Peliosis of the female adrenal cortex of the aging rat

Foci of apparent peliosis are regularly observed in the mid-zone of the adrenal cortex in female rats older than 600 days. The changes present range from ectasis of the sinusoids to extensive cystic change of the whole organ. This lesion occurs almost exclusively in female animals and was seen in only one of 50 male animals older than 600 days examined. Experimental stimulation or inhibition did not influence adrenal peliosis. Electron microscopically, there was marked pericapillary edema with collapse of the capillaries, and erythrocytes and thrombocytes were seen infiltrating the edema. Fibrin accumulated in the larger foci. Degenerative alterations were not observed either in the epithelial cells of the cortex or in mesenchymal cells. The pathogenesis is unknown, but the possible role of constant estrus in aging female rats will be discussed.