We investigated the effect of intravenous infusions of the therapeutically available amino acid solutions Moripron and Morihepamin (Roussel Morishita, Osaka, Japan) on gallbladder contraction and cholecystokinin (CCK) release in healthy male volunteers. Plasma CCK levels were measured by radioimmunoassay, using the antibody OAL-656, which is specific for the aminoterminus of CCK-8 and thus recognizes biologically active forms of all CCKs. The volume of the gallbladder was calculated by ultrasonographic measurements. Intravenous infusion of Moripron at the rate of 3.33 ml/min for 60 min, caused gallbladder contraction, with a peak response of 31.3 +/- 8.6% of the fasting volume at 45-60 min, and a significant increase in plasma CCK concentration, from 1.8 +/- 0.2 pmol/l to a peak of 9.9 +/- 1.5 pmol/l, at 30-45 min. The maximum gallbladder contraction and the peak CCK release during the Moripron infusion were not significantly different from findings after a test meal. There was a close relationship between the peak plasma CCK concentration and the maximal gallbladder contraction during the administration of Moripron, and this agent, even when infused at the rate of 1.67 ml/min, significantly increased plasma CCK levels and gallbladder contraction. Intravenous infusion of Morihepamin had no significant influence on gallbladder volume or plasma CCK levels. The discrepancy in responses appeared to be related to differences in composition between Moripron and Morihepamin, and not to the total dose of amino acid. Intravenous infusions of amino acids appear to have different effects on gallbladder contraction and plasma CCK secretion depending on the amino acids composition. Our findings suggest that an intravenous infusion of Moripron could be used for the prophylaxis of acute acalculous cholecystitis and sludge formation due to reduced biliary motility in patients on total parenteral nutrition.