Aging of the male reproductive system.

Reproductive and sexual physiology, changes in body composition and mental performance in the aging male cannot simply be reduced to presumptive hypogonadism defined by low androgen serum levels or by decreasing levels of growth hormone (GH) and melatonin. Morphological changes in organs at different regulatory levels of hormonal networks governing, for example reproduction, such as diminished hypothalamic pulse generator mass, focal degeneration and loss of Leydig cells in testicular tissue, lead to diminished reserve capacities in production and to loss of coordinated pulsatile release of hypothalamic neuropeptides (e.g. gonadotropin releasing hormone, GnRH) and consequently diminished release of pituitary protein and glycoprotein hormones and testicular steroid hormones. Owing to presumptive alterations in feedback sensitivity, decreased testosterone levels do not necessarily upregulate pituitary LH secretion. Alternatively, increased serum levels of LH and FSH can be observed in old men either because of primary hypogonadism or to decreased hypothalamic opioid tone. In general, endocrine functions are sufficient to maintain fertility in elderly men because, except for sperm motility, quantitative and qualitative functional semen parameters are apparently not affected by age. Nevertheless, reduced endocrine and organic functions might become critical at different levels, with high inter-individual variability, of the hypothalamo/pituitary/gonadal-axis. One of the most intriguing organic manifestations of male aging is benign prostatic hyperplasia (BPH), the pathologic prevalence of which closely matches age. Age-associated changes in the endocrine system and in local networks of epithelial, stromal and luminal factors may play important roles in BPH development.