Effect of Intermittent Infusion of LH-Releasing Hormone on Serum LH and FSH Levels In Immature Male Rats

The effect of intermittent intravenous infusions of LH RH on serum LH and FSH levels was studied in immature male rats. At the end of the infusion, serum LH and FSH levels were higher than those after saline infusion. One hr after the end of infusion of LH RH, serum LH levels fell, reaching saline control values, but FSH levels remained higher. Moreover, a pulsative pattern of LH release but not of FSH, was obtained during the intermittent infusion with LH RH. These findings indicate that under appropriate conditions after the administration of LH RH, it is possible to find high FSH levels without a concomitant rise of LH levels. The continued elevation of FSH may be explained by the longer biological half life of FSH. Estradiol benzoate depressed the basal serum FSH level and augmented LH release after intermittent infusion with LH RH, indicating that estrogen modified FSH/LH ratio. The results suggest that discordance of plasma LH and FSH levels which is occasionally observed in some physiological conditions does not necessarily indicate the presence of another FSH RH which is distinct from LH RH decapeptide.