[Effect of CCK receptor antagonists on plasma CCK bioassay]

Fasting and postprandial plasma CCK levels of 102 normal subjects were measured by bioassay with dispersed rat pancreatic acini. The reference values ranged from 0 to 4.2 pmol/L (CCK-8 equivalents) for fasting and from 1.1 to 13.5 pmol/L for postprandial state. There was no significant difference between male and female, or in different age groups. The effects of CCK receptor antagonists of 3 different categories on CCK bioactivity in plasma measured by the bioassay were investigated. L 364,718 (5 nmol/L), proglumide (1.0 mmol/L), or Bt2-cGMP (0.1 mmol/L) was either extracted by SEP-PAK C18 cartridges together with human plasma containing 8 pmol/L of CCK-8, or added into the plasma extracts before the assay. The CCK bioactivity was inhibited by all of the 3 CCK antagonists. The action of L364,718 could be eliminated by the procedure of plasma extraction, but not of proglumide or Bt2-cGMP. It was suggested that CCK bioassay can be used even if L364,718 was administered. However, CCK cannot be measured accurately if there are proglumide or Bt2-cGMP in the plasma.