Effect of a test meal, duodenal acidification, and tetragastrin on the plasma concentration of beta-endorphin-like immunoreactivity in man.

The effects of various test materials on plasma beta-endorphin-like immunoreactivity (beta-EpLI) were investigated in man using a specific radioimmunoassay developed by the authors. Plasma beta-EpLI was determined after extraction by the acid/acetone method (recovery 73 +/- 5%). The intraassay and interassay coefficients of variation were 5.0% and 7.6%, respectively. The plasma concentrations of human beta-EpLI in normal subjects were 11.6 +/- 4.0 pmol/l for men (n = 23) and 10.7 +/- 4.8 pmol/l for women (n = 27). Ingestion of a test meal (150 g of Campbell's condensed meat soup) resulted in a biphasic rise in plasma beta-EpLI from the basal level of 4.4 +/- 1.0 pmol/l to 29.2 +/- 1.9 pmol/l after 5 min and 24.8 +/- 6.7 pmol/l after 90 min. Intraduodenal infusion of 115 ml of 0.1 M HCl over 10 min increased the plasma beta-EpLI level from 8.7 +/- 0.5 pmol/l to 15.5 +/- 0.4 pmol/l at 10 min after the start of infusion, but the level rapidly returned to the initial value after the end of the infusion. Intramuscular injection of 4 micrograms/kg body weight of tetragastrin markedly stimulated gastric acid output and beta-EpLI release, but pretreatment with 10 mg of histamine H2 receptor antagonist inhibited the gastric acid output and plasma beta-EpLI release induced by tetragastrin. These results indicate that beta-EpLI release is stimulated by ingestion of meat soup, duodenal acidification and tetragastrin administration. It is suggested that gastric acid participates, at least in part, in postprandial release of beta-EpLI, probably from the gastrointestinal tract.