INHIBIN AND AGE IN MEN

OBJECTIVE Normal elderly men are reported to have decreased testicular function despite elevated gonadotrophin levels. We wished therefore to determine if changes in testicular function occur over the age range 19-60 years. DESIGN Single fasting blood samples were obtained between 0800 and 0900 h. PATIENTS Working men in a large industrial company between the ages of 19 and 60 years participated in the study. MEASUREMENTS FSH, serum immunoreactive inhibin and total testosterone were measured, the latter two as measurements of Sertoli and Leydig cell function respectively. RESULTS The mean baseline serum immunoreactive inhibin level was significantly lower in men from the older age groups, 31-40 years (479 U/l), 41-50 years (439 U/l) and 51-60 years (415 U/l) than in men from the youngest age group, 21-30 years (613 U/l) while serum FSH was higher in men from the older age groups, 41-50 years (3.7 lU/l) and 51-60 years (6.1 lU/l) than in men from the youngest age group, 21-30 years (2.6 lU/l). There appears to be a change in both FSH and inhibin production, consistent with a primary decline in testicular function. There was no significant difference in testosterone levels between the older age group, age 51-60 years and the younger age group, age 21-30 years. However, testosterone levels were significantly lower in the 41-50 year age group, when compared with the 21-30 year, this significance levelling out at about age 45 years. CONCLUSION The data are consistent with the hypothesis that immunoreactive inhibin reflects inhibin bioactivity, and that inhibin plays a role in the feedback control of FSH secretion in men.