Synthesis of Some Structural Analogues of LH-RH Modified in Position 5, theirin vivoandin vitroGonadotropin-releasing Activity and Immunoreactivity

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: Text Table Text. 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] aa 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%