STUDIES ON THE STRUCTURE-ACTIVITY OF MOTILIN IN-VIVO - EFFECT OF MOTILIN SYNTHETIC ANALOGS IN CONSCIOUS DOG

Synthetic analogues of motilin were tested for their capacity to stimu late the intestinal motor activity of the conscious dog. Physiological doses (75 pmol/kg) of motilin 1-22 and of motilin fragments 1-21, 1-2 0 and 1-19 induced premature periods of phase III activity in all test ed animals. Motilin fragments 1-15, 1-12, 1-11 and 1-10 failed to infl uence the intestinal myoelectrical activity even when given at doses 1 0-times superior (750 pmol/kg). Motilin-like-immunoreactivity was meas ured in plasma during the analogues infusion. During the infusion of t he bioactive analogues (1-22, 1-21, 1-20, 1-19), plasma motilin increa sed by 174 +/- 25 fmol/ml while a small rise (22 +/- 7.6 fmol) was not ed with the inactive fragments (P < 0.001). Our data are in agreement with the in vitro findings that the N-terminal portion of the motilin molecule is responsable for its biological activity and suggests that the middle portion of the molecule is important to prevent degradation and maintain biological activity in vivo.