Fasting and postprandial plasma GIP values in man measured with seven different antisera

In the present study GIP was measured with seven different antisera in fasting and postprandial plasma samples from eight healthy subjects. The mean fasting plasma GIP values ranged from 12 to 92 pmol/l, and the mean postprandial GIP values from 35 to 235 pmol/l. All seven antisera recognized three molecular forms of GIP, and none showed any appreciable crossreactivity with other gastrointestinal peptides. However, a remarkable range in crossreactivity, from 78 to 8%, with C-terminal GIP was found. The most likely explanation for the great differences in plasma GIP values measured appears to be differences in crossreactivity with human GIP.