Dose-related effects of the synthetic met-enkephalin analogue FK 33-824 on esophageal motor activity in healthy humans

The effects of FK 33-824, a methionine enkephalin analogue, 313, 625, 1250, 2500, and 5000 ng/kg body wt intramuscularly, on esophageal motor activity and cardiovascular and central nervous functions were studied in 8 healthy men. In the lower one-third of the esophagus, amplitude and duration of swallow contractions increased dose-dependently within 15 min after administration. In the middle one-third, amplitudes increased only slightly, whereas no systematic changes occurred in the upper one-third. The propagation velocity of the deglutitive wave accelerated dose-dependently between 15 and 10 cm as well as between 10 and 5 cm above the lower esophageal sphincter, the acceleration being more pronounced in the distal segment. Heart rate and systolic and diastolic blood pressure increased dose-relatedly, while no effects were found on electroencephalogram and reaction time. These results, together with earlier findings, support the notion of a participation of enkephalins in the regulation of the smooth muscle esophagus.