A radioimmunoabsorbent assay for plasma somatostatin

A solid phase radioimmunoassay for determination of immunoreactive somatostatin (IRS) in plasma is described. Plasma samples obtained from 30 apparently healthy persons and from 5 anaesthetized pigs were extracted with acetone-petroleum ether. The antibodies (R 141 and R 101) were conjugated to cyanogenbromide activated microcrystalline cellulose. Tyr1-somatostatin was iodinated according to the lactoperoxidase method. After extraction the recovery of somatostatin varied between 80 and 118%. The sensitivity of the assay was 5--10 pg/ml and the intra- and interassay variation ranged between 8 and 20%. The mean (+/- S.D.) value of IRS in systemic blood in man was 77 (+/- 19) pg/ml. Intravenous administration of 10 micrograms/kg synthetic somatostatin to anaesthetized pigs was followed by a 20-fold increase in plasma IRS. The hypersomatostatinemia rapidly vanished with a half-life of 3.5 min. The level of IRS in cerebrospinal fluid was unchanged by intravenous somatostatin at this dose.