Delayed Anovulatory Syndrome Induced by Estradiol in Female C57BL/6J Mice: Age-like Neuroendocrine, but Not Ovarian, Impairments 1

Abstract

These studies describe induction of a delayed anovulatory syndrome (DAS) by estradiol (E2) in female C57BL/6J mice. Six days after birth, female mice were injected s.c. with 0.1 micrograms estradiol benzoate or oil. Over 90% of the oil-injected controls exhibited estrous cycles from 2 to 9 mo of age. In contrast, 60% of the E2-injected mice exhibited estrous cycles at 2 mo of age but were acyclic by 9 mo; these mice were considered to have exhibited a DAS, and had longer cycles than controls. At 12 mo, ovarian impairments were assessed by examining 1) ovulation after s.c. injection of 5 IU human chorionic gonadotropin (hCG), and 2) estrous cycles after grafting into young (3-mo-old) hosts. Simultaneously, neuroendocrine impairments were assessed by examining 1) the surge of luteinizing hormone (LH) induced by E2 implants after ovariectomy, and 2) estrous cycles after receiving ovarian grafts from 3-mo-old mice. Ovaries from DAS and control mice ovulated equally in response to hCG. Ovaries from DAS mice grafted into young ovariectomized hosts supported 30% more cycles, of shorter period, compared with ovaries from control donors. However, the E2-induced LH surge was 50% smaller in DAS mice than in controls. Ovariectomized DAS hosts with ovarian grafts from young mice supported 70% fewer estrous cycles, of longer period, compared with ovariectomized control hosts with young grafts. We conclude that the E2-induced DAS in female mice is not due to ovarian impairments, but seems to result from neuroendocrine impairments.

Controlled Neonatal Exposure to Estrogens: A Suitable Tool for Reproductive Aging Studies in the Female Rat1

“…Females bearing neonatal EB implants for 24 h exhibited a delayed anovulatory syndrome (DAS) such as has been reported with low doses of steroids [14,18,19]. However, our rats displayed regular estrous cycles for a longer period than those given 10 jig testosterone propionate [14] (50% sterile at 45 days of age), or than mice injected with 0.1 jig EB (60% showed longer cycles than controls at 60 days) [18].…”

“…However, our rats displayed regular estrous cycles for a longer period than those given 10 jig testosterone propionate [14] (50% sterile at 45 days of age), or than mice injected with 0.1 jig EB (60% showed longer cycles than controls at 60 days) [18]. In addition, our pattern of treatment was more effective: 92% of our rats expressed DAS by 5 mo, whereas 30% of the mice treated s.c. with low doses of E 2 [18] were refractory to the treatment.…”

“…However, our rats displayed regular estrous cycles for a longer period than those given 10 jig testosterone propionate [14] (50% sterile at 45 days of age), or than mice injected with 0.1 jig EB (60% showed longer cycles than controls at 60 days) [18]. In addition, our pattern of treatment was more effective: 92% of our rats expressed DAS by 5 mo, whereas 30% of the mice treated s.c. with low doses of E 2 [18] were refractory to the treatment. To explain the improved results of our treatment, attention must be paid to the large dose of E 2 used, which always assures supramaximal effects; results produced by low doses are dependent on the binding capacity of specific proteins (alfa-phetoprotein) in the circulation [23].…”

“…In addition, perinatal life is the period of greatest sensitivity to the organizing effects of gonadal steroids [8,14], and large doses of estrogens given s.c. to neonate rats result in neuroendocrine alterations [15,16] that resemble those observed in spontaneously aging females already in constant estrus [6,7]. Thus, to reproduce the conditions that cause early reproductive senescence, small doses of steroids have been administered early in life with the result that the animals displayed regular estrus cycles after puberty but soon failed to ovulate [14,[17][18][19]. This phenomenon has been referred to as delayed anovulatory syndrome (DAS).…”

“…This phenomenon has been referred to as delayed anovulatory syndrome (DAS). However, since significant refractoriness to the treatment has been reported [14,18,19], long-term studies are required to verify which animals will express DAS in order to be used as an early aging model.…”