Inhibition of maturational changes in Leydig cell function by treatment of rats with an agonist of LH-RH.

Daily treatment of immature (30-day-old) male rats for 40 days with 50 ng of an agonist of LH-RH impaired normal development of Leydig cell function. This treatment partly or completely inhibited maturational increases in (1) the serum levels of testosterone, (2) seminal vesicle weight, (3) the in-vitro steroidogenic responsiveness of the testis, and (4) the in-vitro testicular binding of 125I-labelled hCG. In contrast, twice-weekly treatment of immature or adult rats with 50 ng LH-RH agonist had only minor effects on Leydig cell function, although hCG-binding was always significantly reduced. Testicular growth in immature rats was unaffected by daily injection of LH-RH agonist whereas twice-weekly treatment caused a small reduction in weight. None of the treatments had any major consistent effect on the pituitary or serum levels of gonadotrophins and prolactin, although daily treatment with the LH-RH agonist clearly reduced the responsiveness of the pituitary to the agonist, in terms of the amounts of LH and FSH released.