Age-Related Changes in the Male Reproductive System

In male mammals, changes at all levels of the hypothalamic-pituitary-testicular axis, including alterations in the GnRH pulse generator, gonadotropin secretion, and testicular steroidogenesis, in addition to alterations of feed-forward and feed-back relationships contribute to the age-related decline in circulating testosterone concentrations. The rate of age-related decline in testosterone levels is affected by the presence of chronic illness, adiposity, medication, sampling time, and the methods of testosterone measurement. Epidemiologic surveys reveal an association of low testosterone levels with changes in sexual function, body composition, physical function and mobility, and increased risk of diabetes, late life persistent depressive disorder (dysthymia), unexplained anemia of aging, osteoporosis and bone fractures. Age-related decline in testosterone should be distinguished from classical hypogonadism due to known diseases of the hypothalamus, pituitary, and the testis. In young hypogonadal men who have a known disease of the hypothalamus, pituitary, and testis, testosterone therapy is generally beneficial and has been associated with a low frequency of adverse events. However, neither the long-term benefits in improved health outcomes nor the long-term risks of testosterone therapy are known in older men with age-related decline in testosterone levels. Well-conducted randomized trials have found that testosterone replacement of older men with unequivocally low testosterone levels improves sexual desire, erectile function, and overall sexual activity; lean body mass, muscle strength and some measures of physical function and mobility; areal and volumetric bone density and bone strength; depressive symptoms; and corrects anemia of aging. Testosterone treatment does not worsen lower urinary tract symptoms but the effects of long-term testosterone treatment on the risk of prostate cancer and major adverse cardiovascular events remain unknown. Although testicular morphology, semen production, and fertility are maintained up to a very old age in men, there is clear evidence of decreased fecundity with advancing age and an increased risk of specific genetic disorders related to paternal age among the offspring of older men. Thus, reproductive aging of men is emerging as an important public health problem whose serious societal consequences go far beyond the quality-of-life issues related to low testosterone levels. For complete coverage of all related areas of Endocrinology, please visit our on-line FREE web-text, WWW.ENDOTEXT.ORG.