Solutions containing synthetic LRF (0.015, 0.15, 1.5, or 15 μM) were infused into a hypophysial portal vessel of adult, male rats at 2 μl/min for 30 min. A solution of NaCl (0.15M) was used as the solvent control. The release of LH and FSH was evaluated by determining the concentrations of these hormones in plasma of arterial blood of the recipient animals prior to, during, and after the infusion of LRF. Prior to the infusion, the plasma concentrations of LH and FSH in all animals were similar. The infusion of 0.15M NaCl had little effect on the release of LH or FSH. After the infusion of 0.015, 0.15, 1.5, or 15 μM LRF for 10 min, an increase in the plasma concentration of LH was seen. Throughout the infusion, the plasma LH levels continued to increase, attaining values after 30 min that were as much as 5-fold greater than the resting levels in some cases. Although the concentration of LRF in the infused solution varied from 0.015 to 15 μM, no dose-response relationship was seen, suggesting that maximal stimulation was induced by the smallest concentration of LRF. After the infusion was stopped, the LH levels in plasma fell slowly. However, 90 min after the infusion ceased, the LH levels were still markedly elevated over the pre-infusion values. LRF at 0.015 μM had no effect on FSH release. However, LRF at 0.15, 1.5, or 15 (μM stimulated the release of FSH. The results agree with the reports of other investigations that show that synthetic LRF stimulates the release of LH and of FSH.
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