Plasma reproductive hormones in normal and vasectomized Chinese males

The longterm effect of vasectomy on plasma reproductive hormones was investigated in a cross-sectional study conducted in Chinas Sichuan Province. The study group included 505 men 30-73 years of age who had undergone vasectomy 1-25 years earlier and 298 nonvasectomized controls in the same age group. The mean age of vasectomized men was 48.8 years and that if controls was 46.3 years. The mean duration since vasectomy was 12.4 years in the study group. Study findings revealed a significant increase in plasma testosterone and follicle-stimulating hormone (FSH) with time since vasectomy but no difference was observed between the vasectomized men and nonvasectomized controls when age effects were controlled. The mean testosterone level in men vasectomized 1-11 years earlier (22.8 nmol/1) was significantly below that for nonvasectomized controls (24.9 mmol/1); however in men vasectomized 12-15 16-19 and 20+ years earlier the mean testosterone levels were higher (26.4 24.6 and 29.0 mmol/1 respectively). Plasma luteinizing hormone (LH) levels increased with age in both groups but the levels did not differ according to time since vasectomy. The rise in plasma LH without an associated decrease in testosterone levels in healthy men suggests either that the aging testis requires higher concentrations of gonadotropins to maintain its testosterone biosynthetic efficiency or that the biological to immunological ratio of the circulating LH may decrease with age.