[Biological manifestations of the andropause]

Aging in men is accompanied by signs of decreased virility and fertility: testicular volume, muscle mass, pilosity, sexual activity, daily production of spermatozoa, plasma testosterone levels, the number of Leydig cells and blood supply of the testicles decrease significantly with age. The pulsatility of LH levels in young and elderly men has been studied by taking plasma samples with an interval of 10 minutes for 12 hours. Age alterations at the hypothalamic-pituitary levels of testosterone production and an increase in gonadostat sensitivity to hormonal influences realized via the feedback mechanism are found. Whenever androgen therapy of eugonadal elderly men is considered, a sufficient dosage should be administered, as otherwise, due to the feedback effects, administered androgens, suppressing endogenous secretion might not increase plasma-testosterone levels. Changes in neurotransmitters and neuromodulators play a determinant role in the sexual behaviour of elderly men.