Comparable Testosterone Responses Are Produced by Constant Infusion of LH or GnRH in Normal Men

Summary

Luteinizing hormone (LH) was infused continuously at a rate of 1.3 IU/min to 4 normal adult men. A 4 to 5-fold increase in serum LH was noted by 8 hours. Serum FSH declined steadily throughout the infusion period in the face of rising concentrations of gonadal steroids. Basal plasma testosterone of 4.7 ± 0.4 ng/ml rose progressively to a peak of 11.1 ± 0.9 ng/ml at hour 56 (p < 0.005). A similar pattern was demonstrated by plasma androstenedione. Plasma 17α-hydroxyprogesterone rose from a basal concentration of 0.81 ± 0.14 ng/ml to a peak concentration of 2.6 ± 0.3 ng/ml at hour 36 of the infusion and subsequently declined. A similar course was followed by serum estradiol-17β, which achieved a maximal concentration of 70.0 ± 10.4 pg/ml at hour 36.

Results are compared to those obtained with continuous infusion of GnRH in normal adult men. Testosterone responses were similar, whereas elevations in 17α-hydroxyprogesterone and estradiol were higher following GnRH infusion. This difference may be consequent upon a direct gonadal effect of GnRH, or may be secondary to local regulation of testicular steroidogenesis by estradiol-17β.

Key-Words:

GnRH - LH - Testosterone