Synthesis of Five Cholecystokinin-like Peptides and Determination of Their Analgesic Effects

Five CCK (cholecystokinin)-like peptides [CCK(27-32)amide, CCK-6, CCK-7, Boc-CCK-7 and nonsulfated CCK-7] were prepared by stepwise condensation in combination with fragment condensation by the active ester procedure. The analgesic effects of these CCK-like peptides were measured in the writhing test. The ED50 value of CCK-7 was 1500 nmol/kg (1.8 mg/kg). Boc-CCK-7 appeared to reduce writhing between doses of 1 and 8 mg/kg but did not show a dose-dependent response. Other synthesic peptides produced no response even at a dose of 8 mg/kg. Our results suggested that CCK-7 is one of the shortest CCK-fragments that can retain the analgesic effect.