Stimulation of Release of LH by Synthetic LH-RH in Vivo: I. A Comparative Study of Natural and Synthetic Hormones*

Abstract

Synthetic luteinizing hormone-releasing hormone (LH-RH) was synthesized by Merrifield's solid phase method based on the proposed structure of porcine LH-RH: (pyro)Glu-His-Trp- Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH₂. It was then purified by countercurrent distribution and electrophoresis. LH-releasing activity of the synthetic LH-RH was tested in ovariectomized estrogenprogesterone treated rats. The dosages were expressed by mole based on its tryptophan content. As small a dose as 3.47 × 10–¹² mole induced a significant rise of serum LH. At the same log dose intervals, the dose regression lines for synthetic LH-RH were parallel to those for natural LH-RH. Injection of either the natural or synthetic LH-RH preparations increased serum LH significantly 5 min after injection. The maximum rise in LH was attained between 10 to 20 min after injection. Then, serum LH levels slightly decreased but remained at approximately the same levels up to 60 min after injection. Significant (p < 0.02), but very slight increment of serum FSH was observed only in the rats injected with the high dose (3 × 10–¹² mole) of the natural pure LH-RH, 30 to 60 min after administration. Injection of low dose of the natural LH-RH and high and low dose of the synthetic LH-RH failed to increase serum FSH levels, which would simply be due to an insufficient dose of these materials. These results suggest that synthetic LH-RH behaves in a manner similar to natural LH-RH. (Endocrinology90: 163, 1972)