Plasma levels of secretin in man and dogs: validation of a secretin radioimmunoassay.

We have developed and validated a secretin radioimmunoassay that is sufficiently sensitvie to measure circulating levels of secretin in the plasma of man and dogs. At a final dilution of 1:50,000, the antibody bound 30 percent to 40 percent of radioiodinated (125 I) 6-tyrosyl synthetic secretin. Pure natural porcine secretin was used as a reference standard and a linear dose-response curve was generated with 10 to 1,000 pg. of the polypeptide. Little or no cross-reactivity was found when graded doses of other gastrointestinal polypeptides were assayed in the radioimmunoassay and immunoreactive secretin (IRS) in volumes of serum up to 300 mul could be measured accurately.