Der Einfluß des Alterns auf die endokrinen Funktionen des Mannes

Abstract

From earlier investigations on the morphology of the human testis and sperm it can be stated that in older age the spermatogenic activity is not affected to a greater degree whereas the number of hormone-producing cells — the Leydig cells — decreases with age. Histochemically these cells showed a decrease of lipid constituents in their cytoplasma. In former years the age-depending androgen production in the human male was studied by bioassay of these hormones in the urine. A peak of androgen exretion was found between the ages of 25 und 30 years, followed by a steady decrease; beyond 60 and 70 years of age only a third of the maximum excretion was found. Investigations on the excretion of 17-ketosteroids and their fractions, throughout life, showed a similar relationship to aging, indicating primarily that adrenal precursors of urinary androgens decrease with age. Studies on the function of male secondary sex organs in old age have also been performed: from the third to the seventh decade of life a steady decrease of fructose content in the seminal plasma has been found, suggesting a reduced function of seminal vesicles. In the last years modern methods of steroid analysis gave more precise information about androgens in the older male. The excretion of testosterone glucuronoside — a good parameter for testosterone production in the male — showed a peak in the life span between 25 and 35 years; thereafter a gradual decrease was observed, reaching a constant level in the 7th decade. At this age and afterwards testosterone excretion was only one third of the maximum. In addition measurements of blood production rates of testosterone showed a decrease in older age groups; at the same time the metabolic clearance rate of testosterone was diminished. In contrast to urinary testosterone, the plasma concentration remained high until the 8th or 9th decade of life, a phenomenon which is partly explained by the diminished clearance rate of testosterone. However, a normal testosterone level in plasma cannot guarantee normal androgen action in old age, because the testosterone binding capacity of plasma increases and free plasma testosterone, which is thought to be the really active fraction, decreases with age. Furthermore some observations suggested that certain target organs demonstrated a decreased sensibility to testosterone in older age. In addition testosterone metabolism in the older male seemed to be changed to a more female pattern, especially concerning a greater conversion to 5s-metabolites and androstanediols.