Clinical comparison of natural LH-RH, synthetic LH-RH, and two analogues of LH-RH

Two analogues of LH-RH as well as pure, natural LH-RH were compared with synthetic LH-RH in normal men. The 9-ethylamide LH-RH caused increments in plasma levels of LH and FSH comparable to those caused by synthetic LH-RH given at double the dose level. About twice the amount of the 5-phenylalanine analogue, as compared with synthetic LH-RH was required to release similar amounts of LH and FSH. Prolongation of action was found in some subjects by the addition of 16% gelatin to the im injections and mean maximum peaks may have been delayed when the 9-ethylamide LH-RH was given as a rapid iv injection. Pure natural LH-RH was as potent as the synthetic decapeptide.