[Hormone studies in andrology].

Investigation of endocrine function is mainly performed by measuring plasma levels of the hormones concerned. Their evaluation must take into account the spontaneous alterations of hormonal plasma levels. With regard to gonadotrophins, the short-term episodic peaks of LH are significant. Testosterone levels, as well, show extensive short-term variations; in addition we find a marked circadian rhythm. Seasonal variations of longer duration are possibly superposed. Regarding the evaluation of testosterone levels, we must consider its protein-binding. Only the free fraction of the hormone is biologically active. Concerning the function and secretory capacity of endocrine organs, stimulation tests often provide us with better results than the determination of basal plasma levels. The gonadotropic function of the hypophysis can be stimulated by intravenous application of 100 micrograms GnRH leading to increased blood levels of LH and FSH. The stimulation of the testosterone biosynthesis is achieved by application of hCG. The testosterone plasma levels rise within a few hours; a second peak follows after about 48 hours. Functional tests are also significant regarding the therapeutical prognosis of spermatogenetic disorders treated with gonadotrophins. Their outcome is even better if the secretory capacity of the hypophysis and the Leydig's cell apparatus has been proved sufficient before treatment.