On the Role of Dihydrotestosterone in Regulating Luteinizing Hormone Secretion in Man*

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Abstract
The effect of dihydrotestosterone [17.beta.-hydroxy-5.alpha.-androstone-3-one (DHT)] in the negative regulation of LH [luteinizing hormone, lutropin] was studied throughout 3 mo. of percutaneous administration of this steroid to 6 normal male volunteers and 6 patients with primary testicular hypogonadism. Testosterone (T) was administered according to the same protocol to the 6 hypogonadal patients. Plasma T, DHT, estradiol, sex hormone-binding globulin and LH levels were measured by radioimmunoassay before and weekly during treatment. In normal men, plasma DHT rose regularly from 0.5 .+-. 0.2-3.3 .+-. 0.9 ng/ml after 3 mo. of treatment. Concurrently, T decreased 5.5 .+-. 2.0-2.9 .+-. 0.3 ng/ml and sex hormone-binding globulin levels decreased 1.2 .+-. 0.1-0.9 .+-. 0.05 mg/l. Mean basal LH levels remained stable between 1.9 .+-. 1.3-3.1 .+-. 1.1 mIU MRC [Medical Research Council units] LH 68/40 per ml throughout treatment. In hypogonadal men after DHT treatment, basal LH levels were not suppressed. After T administration, plasma LH decreased 19.8 .+-. 5.4 mIU/ml to normal levels (3.4 .+-. 2.7 mIU/ml). Evidently, high levels of plasma DHT, maintained over a long period, were unable to lower plasma LH in normal or hypogonadal patients; during the same length of time, high levels of plasma T were perfectly capable of achieving feedback regulation of LH secretion. It seems unlikely that circulating DHT plays an important role in the physiological regulation of LH secretion.