FURTHER STUDIES ON HYPOTHALAMIC-PITUITARY-TESTICULAR FUNCTION IN OLD RATS

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Abstract
Hypothalamic-pituitary-gonadal axis dysfunction in old age was studied in 24 mo. old male Wistar rats which were compared with 3 mo. old animals. The hypothalamic LH-RH [luliberin] content and the pituitary LH [lutropin] were significantly lower in the old than in the young adult animals. The plasma concentrations of LH and testosterone [T] were significantly higher in the young rats. The primary cause of these age-dependent changes probably is a hypothalamic dysfunction. When isolated Leydig cells of young and old rats were incubated in vitro, the T secretion per cell was significantly smaller in old than in young cells with or without hCG [human chorionic gonadotropin] stimulation. In vivo stimulation of rats by i.v. injection of biologically active iodinated hCG revealed that the intratesticular uptake of the gonadotropin was not different in young and old rats. The T response was significantly reduced in old age. An in vitro desensitization experiment, in which the LH receptor capacity was artificially reduced demonstrated that the 40% reduction of receptor capacity in old testes as described earlier will not impair the testicular uptake of gonadotropin from blood. Repeated injection of hCG results in equally elevated T concentrations in young and old rats.