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Experimentally Induced Androgen Depletion Accentuates Ethnicity-Related Contrasts in Luteinizing Hormone Secretion in Asian and Caucasian Men

Division of Endocrinology and Metabolism (J.D.V.), Department of Internal Medicine, Mayo Medical and Graduate Schools of Medicine, General Clinical Research Center, Mayo Clinic, Rochester, Minnesota 55905; Department of Internal Medicine and General Clinical Research Center (A.B., R.S.S., C.W.), Harbor-University of California at Los Angeles Medical Center, Torrance, California 90509; and Endocrine Service, Medical Section (A.I.), Salem Veterans Affairs Medical Center, Salem, Virginia 24153

Address all correspondence and requests for reprints to: Johannes D. Veldhuis, Division of Endocrinology and Metabolism, Department of Internal Medicine, Mayo Medical and Graduate Schools of Medicine, General Clinical Research Center, Mayo Clinic, Rochester, Minnesota 55905. E-mail: veldhuis.johannes{at}mayo.edu.

The basis for ethnicity-related distinctions in gonadotropin secretion are unknown but may have important populational and physiological implications. In male contraceptive trials, exogenous testosterone and progestins suppress spermatogenesis to a greater degree in Asian than Caucasian men. In addition, iv infusion of testosterone inhibits LH release more in Asian than Caucasian volunteers. We test the converse postulate that experimental reduction of androgen-dependent negative feedback by way of the steroidogenic inhibitor combination ketoconazole/dexamethasone will unveil ethnicity-related mechanisms of regulated LH secretion in young men. LH release was monitored by sampling blood every 10 min for 24 h followed by immunoradiometric assay, model-free pulse detection, an entropy (regulatory) statistic, and cosine regression. Statistical comparisons revealed that healthy young Asian and Caucasian men maintain comparable baseline concentrations of LH, testosterone, estradiol, SHBG, and molar testosterone to SHBG ratios. In contrast, the two ethnic groups differ prominently in each of basal, pulsatile, entropic, and 24-h rhythmic LH adaptations to short-term androgen withdrawal. Therefore, we postulate that physiological nonuniformity of sex steroid-dependent negative feedback in particular may contribute to populational diversity in LH regulation.