Effect of somatostatin on blood levels of motilin and the interdigestive myoelectric complex in dogs.

A) Radioimmunoassay for motilin Synthetic porcine motilin (gift from Dr. H. C. Beyerman, Guelph, Netherlands) was iodinated by Hunter and Greenwood's technique (1963). Motilin labeled with 125I was purified on G-10 Sephadex and CM Sephadex G-25 columns. Motilin antibody (obtained from Dr. Yanaihara, Shizuoka, Japan) was used in a final dilution of 1/200,000. This antibody did not cross react with 10 pmol of gastrin 17, secretin, pancreatic polypeptide, bombesin, VIP, GIP or somatostatin. The antibody was specific for the central portion of motilin. At a final dilution of 1:10, the assay was sensitive to 50pg/m/ in plasma and the ID50 was 300pg/m/ of synthetic motilin added to plasma. The intra-assay variation was between 4.5 and 6.6% and the inter-assay variation, was 8.6% when tested with plasma motilin concentrations between 100 and 1000pg/m/. B) Dog experiments Under general anesthesia, monopolar silver-silver chloride electrodes were implanted to the serosal surface of the antrum and small intestine of mongrel female dogs (Carlson et al., 1975). Recording sessions on conscious animals were begun 2 weeks postoperatively. The dogs were fasted for 15hr before each experiment. Recordings were made with an 8 channel Brush Mark 200 recorder with the cannula used as an indifferent electrode. The four phases of the interdigestive complex were identified by visual inspection of the electromyograph (Code and Marlett, 1975). Part 1: Normal cycles of motilin and interdigestive activity. Three dogs were observed in a basal state for 3 consecutive cycles of interdigestive myoelectric complexes. Through an indwelling intravenous catheter, 3ml samples of blood were collected in EDTA tubes at 10min intervals during the whole experiment. Part 2: Effects of exogenous GH-RIH (somatostatin on normal cycles. Each experiment was performed once on each of 4 dogs. Thirty min after the end of a recorded activity front (phase III) in the duodenum, GH-RIH (Boeringher Mannheim Biochemicals) was infused at 2.5ƒÊg/kg/h or 0.625ƒÊg/kg/h for 3hr by a Harvard pump. Each dose was administered on a separate day. In an additional experiment, 2 animals received 5ƒÊg/kg/h. Part 3: Effect of exogenous GH-RIH on activity induced by exogenous motilin. Each experiment was