Release of secretin--plasma levels reproduced by exogenous infusion.

Infusion of 0.1 M HCl (0.5 mmol/kg/hr over 20 minutes) into the duodenum of each of seven normal subjects led to a significant rise (P less than 0.05) in mean plasma secretion levels from 3.0 +/- 2.2 (SE) to 15 +/- 4.0 pmol/l. Intravenous infusion of secretin at a rate of 6.6 pmol/kg/hr (0.08 clinical units/kg/hr) reproduced the peak plasma levels of secretin observed during duodenal acidification. However, there was no detectable (2.5 pmol/l) change in plasma secretin after oral protein or glucose.