Direct Feedback Inhibition by Endogenous Testosterone on the Pituitary in Man

Abstract

Synthetic luteinizing hormone-releasing factor (LRF) was injected iv to 2 healthy menat successive 1-week intervals with increasing amounts of LRF from 50 to 800 μg and the effects on LH and testosterone titers just before and after successive stimulations were studied. The weekly baseline levels of plasma LH progressively decreased seven days after administrationof increasing amounts of injected LRF. Baseline LH titers fell to the lower portion of the normal range (48 ng/ml) in one man and to under the normal range (29 ng/ml) in the other. Higher peak values of plasma LH (up to 507 and 932 ng/ml) response to LRF occurred within 1 h with increased injected LRF from 50 to 100 or 200 μg. With larger doses of LRF, the peak values of plasma LH were much lower, as low as 185 and 277 ng/ml. These titers were close to the basal normal range. Weekly baseline titers of testosterone increased markedly following increased LRF. Peak plasma testosterone levels occurred within 180 min of each LRF stimulation. Testoster...