Uneven and transient secretin release after a liquid test meal

In order to test the hypothesis that secretin may be released intermittently after feeding, the plasma secretin concentration was measured at short intervals, and the duodenal pH continuously recorded, after a liquid test meal in 10 human subjects. Secretin was measured with a radioimmunoassay in which the entire molecule is specifically recognized and the immunoreactivities of human secretin and of the porcine peptide used as standard are similar. In the total group, no significant variation of the mean plasma secretin concentration above basal was observed within 45 min after feeding. Analysis of the individual patterns revealed that secretin was released transiently in 5 of the 10 subjects, namely those showing variations of the duodenal pH down to or below 4.0 at some time after the meal. The mean peak delta secretin in these subjects was 7.2 pg ml-1 of plasma. In 7 additional subjects, bolus intravenous injections of 0.005 and 0.01 clinical units kg-1 of porcine secretin resulted in peak delta secretin concentrations of 5.5 and 10.5 pg ml-1, respectively, and were followed by a significant increase of bicarbonate output in the duodenal aspirate. These results indicate that secretin is released unevenly and intermittently in the early period after a liquid meal in man, in amounts that seem sufficient for the initiation of a significant bicarbonate response.