Role of Decreased Numbers of Follicles on Reproductive Performance in Young and Aged Rats1

Abstract

The primary objectives of this study were to: 1) determine if removal of 1.5 ovaries from young rats would mimic reproductive characteristics that normally occur with advancing age and 2) determine if removal of 1.5 ovaries from aged rats would further advance the process of reproductive aging. Removal of 1.5 ovaries increased the number of young (P less than 0.05) and old (P less than 0.01) rats that exhibited abnormal estrous cycles. In addition, concentrations of follicle-stimulating hormone (FSH) were higher at both ages in the groups with half an ovary. The increased concentrations of FSH are consistent with a decrease in the number of growing follicles after removal of 1.5 ovaries. All groups had lower concentrations of estradiol (E2) than young controls. There was a significant increase in the number of abnormal embryos with age and removal of 1.5 ovaries when rats were mated during a 5-day estrous cycle, but there was no effect if they were mated during a 4-day estrous cycle. From the results of this study, we conclude that the reduction in ovarian tissue in young and aged rats mimicked several reproductive characteristics of advancing age. Also, an effect of aging on the hypothalamus was evident in this study.

Relationship between the Supply of Primordial Follicles and the Onset of Follicular Growth in Rats1

“…Further support for this hypothesis can be found in studies showing that surgical removal of large amounts of ovarian tissue caused a sustained rise in FSH levels. Removal of 12 ovaries induced a precipitous decline in the number of primordial follicles remaining in the ovarian fragment [17]. Less drastic surgery does not appear to affect the rate of loss of primordial follicles: hemicastration (which causes only a transient rise in gonadotropins) did not hasten loss of follicles with increasing age compared with the rate in intact controls [19].…”

“…Ovaries of a neonatal rat were estimated by one group of investigators to contain 52 000 germ cells [1]; approximately 5000 oocytes remained at four months of age. Other investigators estimated that by one year of age, the number had diminished to approximately 1000 [17]. The age-dependent rate of loss of primordial follicles can be altered by hypophysectomy, which reduces the rate of loss from 30% to only 10% per 20 days in adult mice [18].…”

Progesterone Implants Delay Age-Related Declines in Regular Estrous Cyclicity and the Ovarian Follicular Reserve in Long-Evans Rats1

“…Experimental reduction of the follicular reserve by unilateral ovariectomy advances the loss of regular cyclicity and fertility in rodent species [14,15]. In addition, food restriction delays the onset of reproductive aging and is associated with a delayed loss of primordial follicles from the ovaries [16,17].…”

Effect of Abdominal Vagotomy at Proestrus on Ovarian Weight, Ovarian Antral Follicles, and Serum Levels of Gonadotropins, Estradiol, and Testosterone in the Rat

“…Vagotomy did not affect serum levels of estradiol or tes tosterone at any time, so that a steroidal imbalance [23] in either of these hormones does not account for the FSH rise following vagotomy or for the alterations in follicle popula tions after vagotomy. Vagotomy may have depressed ovar ian inhibin which in turn caused elevated FSH levels.…”