Abstract
Summary
During the luteal phase of the menstrual cycle, rhesus monkeys (M. mulatto) were treated with 50 IU HCG in saline or saline alone, administered intramuscularly. The ten daily treatments were initiated on the day when implantation would have occurred had the cycle been fertile. Plasma estrogen was determined by radioimmunoassay, and progestin was measured by the competitive protein-binding method. Within 24 hr of the first HCG treatment, progestin levels in the blood reached a peak and then declined gradually despite continued treatment. Estrogen levels also increased but did not reach a peak until the fifth day of HCG administration. Like progestin, the estrogen levels then declined even though treatment was continued. Onset of menstruation in these animals was delayed by several days. The saline-treated animals had normal steroid patterns and cycle length. It is proposed that the injection of HCG brings about biochemical changes in the corpus luteum similar to those occurring during early pregnancy.
The skillful laboratory help of Messers. Robert J. Mandetta and James H. Brinkerhoff is gratefully acknowledged. The metyrapone used in this study was kindly supplied by Ciba-Geigy Pharmaceuticals, Inc., Summit, NJ.
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