Fasting gastrointestinal motor and hormone patterns were studied in 11 healthy volunteers. Cyclic motor activity was present in all subjects during fasting, but the duration and site of onset of each cycle were variable, even in the same subject. Fasting gastrin, GIP, and glucagon levels remained low and constant during the 8-hr study, while plasma motilin levels exhibited cyclic variation in 7 of the 11 subjects. Achlorhydria (induced with cimetidine in 5 of the 11 subjects) did not alter the pattern of fasting motor activity or plasma motilin. In the remaining six subjects, the effect of liquid nutrient meals was examined. Ingestion of a sodium chloride bolus failed to disrupt fasting cyclic activity, while all nutrient-containing solutions inhibited gastric phase-2 motor activity, the duration of inhibition being longest for the mixed and lipid meals. All nutrient meals released GIP, while only protein and mixed meals released gastrin, and the lipid meal released motilin. Our study confirms the rhythmicity of interdigestive motor cycles in man and demonstrates their lack of dependence on gastric acid secretion and some relationship to motilin cycles in certain individuals as determined by radioimmunoassay. Transition from fasting to fed pattern (after liquid meals) is characterized by the inhibition of phasic gastric pressure changes in the antrum and the development of irregular activity in the intestine, similar in pattern to fasting phase 2. Because the duration of interruption of the gastric interdigestive pattern by meals depends on their nutrient content, we conclude that dietary composition may be a major determinant of the fasting-fed motor balance in man.
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