Stimulation of Release of FSH and LH by Infusion of LH-RH and Some of its Analogues

Abstract

Previous studies showed that LH-releasing hormone(LH-RH) can stimulate a considerable release of FSH as well as LH in vivo if given by prolonged intravenous infusion. The effect of the duration of the infusion with synthetic LH-RH was investigated in 25-day-old male rats. LH as well as FSH was released in significant amounts after infusion with LH-RH for 30 min, and 1,2, 3, and 4 h. The release of FSH, however, did not show any dose-response relationship when LH-RH was infused for 30 min. On the other hand, if the duration of the infusion was prolonged, a dose-response relationship became apparent. The steepest dose-response curve in terms of FSH release was obtained after 4 h infusion, in the range between 25 and 200 ng of LH-RH. Two peptides (pyro)Glu-His-Trp-NH<sub>2</sub>, which is the N-terminal tripeptide of LH-RH, and (pyro)Glu-Tyr-Arg-Trp-NH<sub>2</sub>, which possesses a low degree of LH-RH activity (1 part in 7,000) but which was said to be devoid of FSH-RH activity, were also infused. (Pyro)Glu-His-Trp-NH<sub>2</sub> did not raise LH or FSH levels in doses of 200–1,000 µg, but (pyro)Glu-Tyr-Arg-Trp-NH<sub>2</sub> was shown to possess a definite FSH-RH activity comparable to its LH-RH activity.