Progesterone secretion remained significantly higher during diestrus in the 5-day cyclic rat than in the 4-day cyclic animal. Injection of a sufficient amount of antiprogesterone serum (APS) at 2300 h on metestrus in a 5-day cycle advances ovulation and completion of the cycle by 1 day in the majority of animals (75 and 80%, respectively). Progesterone (250 micrograms) administered with APS eliminated the effect of the antiserum. Within 2 h after administration of APS, levels of both follicle-stimulating hormone (FSH) and luteinizing hormone (LH) elevated significantly, while a significant elevation of plasma estradiol above the control value followed as late as 36 h after the treatment. None of the 5-day cyclic rats treated with APS showed ovulatory increases of FSH and LH at 1700 h on the second day of diestrus, although 3 of the 4 animals receiving the same treatment ovulated by 1100 h on the following day. The onset of ovulatory release of gonadotropins might have been delayed for several hours in these animals. These results indicate that recurrence of the 5-day cycle is due to an elevated progesterone secretion on the morning of diestrus, and suggest that a prolongation of luteal progesterone secretion in an estrous cycle suppresses gonadotropin secretion. Rather than directly blocking the estrogen triggering of ovulatory LH surge, the prolonged secretion of luteal progesterone may delay the estrogen secretion itself, which decreases the threshold of the neural and/or hypophyseal structures for ovulatory LH release.
Six new cycloartane glycosides (1-6) were isolated from the rhizomes of Curculigo orchioides. The structures of 1-6 were determined by spectroscopic analyses and the results of hydrolytic cleavage. Compounds 1-6, and their common aglycone (1a), were evaluated for cytotoxic activity against HL-60 human leukemia cells. Compounds 1 and 1a showed cytotoxic activity against HL-60 cells with IC(50) values of 9.0 and 1.8 microM, respectively. The cancer cell growth inhibition of 1a was also examined using a panel of 39 human cancer cell lines in the Japanese Foundation for Cancer Research.
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