| Abstract: | Four analogues of LH-RH modified in position 5 have been synthesized using either classical procedures or the solid phase method. The gonadotropin-releasing activities were determined by radioimmunological measurements of LH and FSH in vivo and in vitro and the immunoreactivities by a specific LH-RH radioimmunoassay (RIA). The following relative potencies and immunoractivities were found: | | in vivo | in vitro | Immuno-reactivity | | LH-RH: | 100 % | 100 % | 100 % | | Tyr(Me)5] | -LH-RH: | 8.6% | 6.0% | 40.0% | | Phe5] | -LH-RH: | 42.5% | 27.5% | 17.0% | | Cha5] a Abbreviations were used according to 37]; Cha = cyclohexyl-L-alanine. | -LH-RH: | 22.4% | 27.8% | 10.0% | | Gly5] | -LH-RH: | 0.1% | 0.5% | 0.7% |  Volume 57 , Issue 7 6 November 1974 Pages 2131-2139 |
