| Abstrakt: |
It has been proposed that with aging or delayed ovulation there is an early rise in follicular and plasma levels of estrogen (and probably other steroids) in relation to the time of ovulation. These alterations in hormonal patterns could affect the oocyte and the intrauterine environment and be responsible for the increase in developmental anomalies and embryonic death observed during aging and delayed ovulation. To determine if such hormonal changes occur, follicular and plasma levels of estrone (E1), estradiol (E2), progesterone (P4), androstenedione (A), dehydroepiandrosterone (DHEA) and testosterone (T) were measured in young and old rats with normal and delayed ovulation. One ml of blood and 2 follicles were collected at 0400, 1200 and 2000 h from 1200 h on Day 2 (second day of leucocytic vaginal smear) of the estrous cycle until 2000 h on proestrus. Follicular and plasma levels of the 6 hormones were compared in young and old rats with 4-, 5- and 6-day estrous cycles to determine the relationship of age and length of cycle to hormonal patterns in relation to time of ovulation.In relation to the time of next ovulation, E2, A and T rose 1 day earlier in plasma and follicles of animals with 6-day cycles than in animals with 5-day cycles, and 1 day earlier in animals with 5-day cycles than those with 4-day cycles. Both A and T were present in much greater concentrations in plasma than was E2, while contents of A, T and E2were similar in follicles. Prior to proestrus, plasma P4declined as the previous corpora lutes (CL) ceased to function, while follicular P4showed only a circadian rhythm. Between 1200 and 2000 h on proestrus, there was a large increase in both follicular and plasma P4.The follicular patterns of E1were similar to those of E2, but were only about 20% of the E2content. Plasma concentrations of E1approached those of E2, and showed a circadian rhythm. Plasma DHEA also had a definite circadian rhythm, whereas follicular DHEA was low and did not differ due to time of day, day of cycle or treatment group. The circadian rhythm with a peak at 2000 h for DHEA and E1is consistent with a major adrenal contribution of these 2 steroids to plasma levels.Differences were found in follicular and plasma patterns of E2, A and T due to length of estrous cycle, but not to age of animal. This is in agreement with the proposal that the preovulatory oocyte and the uterus are altered by exposure to an early and prolonged elevation of E2in animals undergoing an induced or spontaneous delay of ovulation. These alterations could be responsible for the increase in developmental defects and embryonic death due to the delayed ovulation which is associated with advanced maternal age. |
