Plasma somatostatin-like immunoreactivity during the interdigestive period in the dog.

To study possible physiologic relationships between somatostatin and the gastric interdigestive contractions (GIC), gastric motor activity, and plasma somatostatin-like immunoreactivity (SLI) concentration were determined simultaneously in four conscious dogs, each of which was studied on two separate occasions. Plasma SLI level was highest during the GIC period and lowest 60 and 80 min after the cessation of the GIC; the mean difference in plasma SLI was 41 +/- 6 pg/ml. When synthetic motilin, a known stimulus of GIC, was infused at a physiologic rate during the period in which plasma SLI levels were low, SLI rose to approximately the same values observed during the contraction period and GIC similar to those that occur spontaneously were observed. When synthetic somatostatin, a known inhibitor of endogenous motilin release, was infused at a rate that raised the plasma SLI to approximately the levels observed during the contraction period (0.1 microgram/kg per h), the appearance of the subsequent GIC was significantly delayed. These results are consistent with a physiological role for somatostatin in the regulation of GIC in dogs and suggest an interrelationship between motilin and somatostatin.