PLASMA-LEVELS OF SECRETIN IN MAN AND DOGS - VALIDATION OF A SECRETIN RADIOIMMUNOASSAY

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  • 1 January 1976
    • journal article
    • research article
    • Vol. 79  (6) , 658-665
Abstract
A secretin radioimmunoassay that is sufficiently sensitive to measure circulating levels of secretin in the plasma of man and dogs was developed and validated. At a final dilution of 1:50,000, the antibody bound 30-40% of radioiodinated (125I) 6-tyrosyl synthetic secretion. Pure natural porcine secretion was used as a reference standard and a linear dose-response curve was generated with 10 to 1000 pg of the polypeptide. Little or no cross-reactivity was found when graded doses of other gastrointestinal polypeptides were assayed in the RIA and immunoreactive secretion (IRS) in volumes of serum up to 300 .mu.l could be measured accurately. Mean basal levels of IRS in the peripheral plasma of 22 normal human subjects was 216 .+-. 11.8 pg/ml, in the peripheral plasma of dogs was 154 .+-. 6.1 pg/ml, and in the portal plasma of dogs was 283 .+-. 22.2 pg/ml. Basal IRS levels inportal plasma were significantly higher than in peripheral plasma (P < 0.05). In studies on the release of secretion in 3 normal human subjects, the mean basal level of secretion in peripheral plasma was 124 .+-. 8 pg/ml. This level was increased to 137 .+-. 6, 137 .+-. 7, 149 .+-. 9, and 169 .+-. 10 pg/ml. during duodenal acidification with 0.15, 0.30, 0.77 and 1.25 meq 0.1N HCl/min. The secretin response was related to the amount of acid used to irrigate the duodenum. In 6 dogs mean basal levels of secretin in the portal vein were 438 .+-. 102 pg/ml. Secretin levels were significantly elevated above basal (P < 0.05) at 5, 10, 15, 20, 25 and 30 min during irrigation of the duodenum with 0.1N HCl and remained elevated for 5 and 10 min after duodenal acidification.

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