The effect of the initial age and body weight on PMS-induced ovulation in immature female rats
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The influence of the age and body weight on PMS-induced ovulation in immature rats was studied. The succeeding estrous cycle after PMS-induced ovulation were also examined. in PMS-treated immature rats.<BR>I. The animals were given a single injection of PMS subcutaneously between 9:0010:00 hr from day 17 to day 26, and were killed 72 hours after PMS to examine oviducts for ova.<BR>None ovulated when PMS was given before day 20 regardless of the amounts of PMS administered. Ovulation was initiated by 3IU of PMS on day 21, 10IU of PMS on day 24, or 30 IU of PMS on day 23.<BR>Bimodal ovulatory effect of PMS on 22-day old Holtzman rats, reported by YING and MEYER (1969), was also observed in 23-, 24-or 25-day old Wistar rats. When PMS administration was delayed until day 26, however, ovulation occurred in all of the animals.<BR>II. The influence of the body weight and days of age of immature rats at the time of PMS treatment on PMS-induced ovulation was also examined. Three IU of PMS was given subcutaneously on day 20, 21 or 22. None ovulated by PMS on day 20, but the heavier group showed a higher ovulation rate by PMS on day 21 or 22 than that of controls. By PMS on day 23, ovulation occurred in most of the animals in controls as well as in the heavier group.<BR>PMS-induced ovulation in immature rats may be dependent upon the days of age rather than the body weight increase.<BR>III. Intact, 25-day old female rats were singly injected with various amounts of PMS and examined. the occurrence of the second vaginal estrus, for which only endogenous gonadotropins are responsible, was examined.<BR>In non-treated controls, the first estrus was observed 37.7±0.4 days of age (mean S. E.) and followed by the second 45.1±0.5 days of age. With 3IU of PMS, the second estrus was observed 38.7±0.5 days of age, 9 days after the first ovulation induced by PMS. With 30IU of PMS, the second estrus was observed 43.1±0.4 days of age with no significant difference as compared with that of controls, though ovulation was regularly induced 28 days of age by that amount of PMS.<BR>It is concluded, therefore, that the first and second estrus were advanced significantly by 3IU ofPMS treatment as compared with those of controls. The advancement of the secondestrus by PMS is assumed to be mediated through the hypothalamus stimulation byincreased release of ovarian estrogens.
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