Reversible inhibition of gonadal functions by a potent gonadotropin-releasing hormone agonist in adult dog.

This study examines the recovery of spermatogenesis, testicular and plasma steroidogenesis and prostatic steroid content 26 weeks following cessation of daily treatment for 16 weeks with [D-Tryp6]LHRH ethylamide (LHRH-A) in the adult dog. While administration of LHRH agonist resulted in testicular and prostatic weight reductions of 40-60%, a complete recovery is observed 26 weeks after cessation of treatment. The number of sperm in LHRH-A-treated dogs declined rapidly in the first 4 weeks, after which no ejaculation or erection is observed in these animals. Spermatogenesis completely recovered four months following cessation of treatment. While testicular steroidogenesis is completely inhibited during the treatment with the agonist peptide, normal levels of testicular steroids are observed with the exception of 17-hydroxypregnenolone, dehydroepiandrosterone and androst-5-ene-3 beta,17 beta-diol which are elevated above control levels and, furthermore, an accumulation of these delta 5-steroids is also observed in the prostate after the end of treatment. Our data strongly suggest that chronic administration of an LHRH agonist may induce, after cessation of treatment, an overproduction of testicular steroids.