Negative Feedback Effects of Chlormadinone Acetate and Ethynylestradiol on Gonadotropin Secretion in Patients with Prostatic Cancer and Male Rats

Serum LH and FSH levels were determined before and after LH-RH injection (100μgi.m.) in patients with prostatic cancer who were chronically treated with either chlormadinone acetate (CMA, 100 mg/day) or ethynylestradiol (EE, 1 mg/day). In patients treated with EE, the levels of serum LH and FSH before and after injection of LH-RH were significantly lower than those in controls. On the other hand in patients treated with CMA, the basal levels of serum gonadotropins did not differ from those in controls, and the increase in gonadotropin after LH-RH injection was comparable to that in controls.To examine the effects of these steroids on the hypothalamo-hypophysial axis in the regulation of gonadotropin secretion, CMA or EE was implanted in castrated male rats. CMA, EE or cholesterol (control) was implanted in the hypothalamic median eminence-arcuate nucleus region through a stainless doublecannula. EE implantation resulted in a 75% decrease in serum LH (p<0.001) and a 38% decrease in serum FSH (p<0.05) from the control levels on day 5 of implantation. On the other hand, CMA implantation induced a 33% decrease in serum LH (p<0.05) from the control level on day 3 of implantation, but no significant change in serum FSH levels. The injection of 2 μg/kg of LH-RH on day 7 of implantation induced significant lowering of LH and FSH levels. There was no significant difference between serum levels of the hormones 20 min after LH-RH injection for these two groups and those for the control group.These studies suggest that EE has a potent negative feedback effect on both LH and FSH secretion, and that CMA has a mild negative feedback effect on LH secretion.