INSULIN RELEASE IN FASTING MAN INDUCED BY IMPURE BUT NOT BY PURE PREPARATIONS OF CHOLECYSTOKININ

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Abstract
Most preparations of cholecystokinin reported to release insulin have been impure. When highly purified preparations of extracted cholecystokinin and also the synthetic C-terminal octapeptide of the hormone became available for use in humans, we investigated their insulinotropic activity in comparison with a cruder preparation of cholecystokinin in 10 fasting non-diabetic subjects. The doses employed were 75 Ivy dog units, except for the synthetic C-terminal octapeptide of cholecystokinin that was given in a dose of 200 Ivy dog units to compensate for a shorter hawn every minute during 10 min after each injection, thereafter at intervals of 5 min. The mean plasma insulin level increased significantly, reaching a peak 4-5 min after iv injection of the cruder cholecystokinin preparation, but after the other two preparations the plasma insulin level was not significantly changed. The blood glucose level was not significantly changed by any of the preparations used. It is concluded that the plasma insulin peak seen in man after i.v. injection of the less highly purified preparation was due not to cholecystokinin but to some other agent present in this less pure preparation. The identity of this factor is discussed.