Testosterone and 17 OH-progesterone responses in men to 3 h LH infusions

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Abstract
LH is recognized as the Leydig cell stimulus for testosterone production. Yet earlier studies of bolus administered human pituitary LH did not result in testosterone elevations and spontaneous LH elevations infrequently cause recognizable parallel rises of testosterone in adult males. Therefore, 10 normal adult volunteers were given 3 h infusions of human pituitary LH A-3 (2 IU/kg) and sampling was continued for 3 h after the gonadotrophin was stopped. Testosterone, the precursor 17 OH-progesterone and LH were determined in blood samples. There was a mean 5.2-fold LH elevation. From a group baseline mean of 698 ng/100 ml ± 72 (± se) testosterone gradually rose and was significantly elevated at 90, 120 and 150 min (787 ± 67 P P < 0.04, and 804 ± 69 P < 0.001, respectively). 17 OH-progesterone was determined on 9 subjects and averaged 142 ng/100 ml ± 16 before LH and gradually rose to 178 ± 18 at 120 min (P < 0.05) and then declined slightly at 150 and 180 min. Both steroids significantly declined between 180 min (end of LH infusion) and 240 min with no further significant concentration changes. The two men with the highest basal testosterone titers showed the smallest testosterone increases, but in both 17 OH-progesterone rose. In conclusion tonic LH stimulation caused mean testosterone and 17 OH-progesterone to peak at 150 min and at 120 min, respectively. Factors within the Leydig cell appear to limit increases of testosterone and 17 OH-progesterone during the first few hours of enchanced gonadotrophin stimulation.