Physiological doses of secretin do not stimulate acute insulin release

To study the effect of physiological increments in plasma secretin concentrations on basal and glucose-stimulated insulin release, bolus iv glucose injections (5 g) were given to normal weight volunteers (less than 108% ideal BW) before, during, and 30 min after a secretin infusion at a rate of 0.125 U/kg.h, raising mean plasma immunoreactive secretin to 35.5 +/- 8.3 pg/ml. Acute insulin responses to glucose were unaffected during or after the secretin infusion. Furthermore, when plasma glucose was elevated to postprandial levels (128--165 mg/dl), a similar secretin infusion also failed to alter acute insulin responses. In addition, no changes in basal glucose or insulin levels were found when endogenous secretin concentrations were increased by intraduodenal acid infusion. Thus, increases in plasma secretin to concentrations seen in the postprandial state fail to alter acute insulin secretion. It is unlikely that secretin plays any role in the intestinal stimulation of insulin secretion.