A rapid enzyme immunoassay for cholectystokinin octapeptide sulfate

A rapid and sensitive enzyme immunoassay (EIA) for cholecystokinin octapeptide sulfate (CCK-8S) has been developed. The assay is based on a double antibody method using N-terminal specific antibody to CCK-8S, and CCK-8S conjugated with horseradish peroxidase as the enzyme labeled antigen. The time for the first incubation was 2 h. The time for the second incubation, during which the first antibody was precipitated using the second antibody which contained polyethylene glycol 6000 as an accelerator of the immune reaction, was 5 min. The total assay time was less than 3 h. Intra- and interassay coefficients of variation were 4.4-5.8 and 2.7-10.97%, respectively. The minimal detectable dose was 2 pg of CCK-8S in this assay. To demonstrate the utility of this EIA, we applied this assay to evaluate changes in the levels of CCK-8S immunoreactivity in various regions of the brain after kainic acid-induced seizures in the rat. This treatment decreased the contents of CCK-8S immunoreactivity in the frontal cortex, amygdala and hippocampus. These data show that this EIA system is rapid and sensitive enough to measure changes in the tissue levels of CCK-8S.