Suppression of Luteinizing Hormone in Castrated Women by the Administration of Human Chorionic Gonadotropin

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Abstract
The suppressive effect of human chorionic gonadotropin (hCG) on luteinizing hormone (LH) and/or LH-β was studied by specific LH-β radioimmunoassay following hCG administration. Eight castrated women were each administered 10,000 IU of hCG in a single intramuscular injection and five women in the control group were injected with saline. The serum level of hCG increased after the injection, reaching 217.6 mlU/ml after 8 h. There was a significant suppression of the LH levels as compared to those of the control group and the pre-injection levels: 68.2% 1 h after injection, 64.7% after 2 h, 65.5% after 4 h, 77.0% after 8 h, 78.6% after 12 h, and 78.2% after 24 h. There was no significant suppression of the follicle-stimulating hormone (FSH) as compared to the preinjection and control values. Serum concentration of estradioli was not detectable either before or after the hCG injection. We conclude that hCG has a suppressive effect on LH and/or LH-β secretion not mediated by estradiol.