Isoproterenol induces activity fronts in fed dogs through somatostatin release

We confirmed previous studies by others that intravenous somatostatin infusions (1.4 and 2.5 micrograms/kg X h) induced jejunal activity fronts in fed dogs. This finding, coupled with earlier demonstrations that somatostatin is released from the stomach and pancreas in vitro by isoproterenol, led us to investigate the possible role of somatostatin in mediating isoproterenol-induced activity fronts. Plasma somatostatin and motilin concentrations were determined after a meat-base meal, before and after isoproterenol infusions (0.5 micrograms/kg X min). Jejunal activity fronts were initiated in 15 of 17 experiments an average of 25 min after the start of the isoproterenol infusion. The concentration of motilin did not change, but somatostatin concentrations increased progressively beginning 15 min after starting the isoproterenol infusion. Thus, isoproterenol released somatostatin in vivo and this release was associated with jejunal activity fronts. The rise in plasma somatostatin concentration was similar to that obtained after somatostatin infusions, although in the latter experiments the activity fronts began soon after initiation of the somatostatin infusion. The results suggest that isoproterenol-induced activity fronts are mediated by somatostatin. We speculate that beta-adrenergic nerves may induce activity fronts through somatostatin release, possibly in situations such as extreme stress.