Introduction
Gonadal function declines with age in both men and women. The sequelae of female gonadal hypofunction are well characterized and substantial: a growing body of evidence implicates female hypogonadism (i.e. reduction in circulating estrogen) in the pathophysiology of mood disorders, Alzheimer's disease, osteoporosis, and heart disease in aging women (Paganini-Hill & Henderson, 1994; Tang et al., 1996; Grady et al., 1992; Robinson et al., 1994). Such knowledge, and the relative ease of estrogen replacement, has led to productive therapeutics research with important public health implications.
But there is no parallel characterization of the male hypothalamic–pituitary–gonadal (HPG) axis. Although it is now known that testosterone (T) secretion declines substantially with age (Araujo et al., 1998; Villareal & Morley, 1994; Dai et al., 1981; Field et al., 1994), the medical and psychiatric sequelae of normative gonadal hypofunction and the potential therapeutic implications are mostly unexplored. Moreover, since hypogonadism commonly presents as a neuropsychiatric symptom complex, delineation of the role of the HPG axis in the psychiatric problems of aging may be of particular relevance. For example, the suicide rate in elderly white males triples from the sixth decade to the ninth decade; in elderly women, it remains unchanged after age 40 (Meehan et al., 1991). It is possible that this difference is related to untreated hypogonadism among men.