Splanchnic nervous control of the stomach of the spiny dogfish, Squalus acanthias.

The splanchnic innervation of the stomach of Squalus acanthias has been studied using an isolated perfused stomach preparation and isolated strip preparations from the smooth muscle of the stomach wall. The stomach contracted in response to splanchnic nerve stimulation, and this response was mimicked by all three putative transmitter substances tested: adrenaline, acetylcholine and 5-hydroxytryptamine. The response to nerve stimulation was not affected by atropine (10(-6) M) or methysergide (10(-6) M), but was abolished by phentolamine (10(-6) M). This concentration of phentolamine had little or no effect on the responses of the stomach to exogenous acetylcholine or 5-hydroxytryptamine, but significantly blocked the response to exogenous adrenaline. The results are interpreted in favour of an adrenergic excitatory splanchnic innervation of the dogfish stomach. A "rebound" contraction of the stomach normally occurred upon cessation of the splanchnic nerve stimulation. This response disappeared together with the primary contraction after administration of phentolamine, suggesting the involvement of an adrenergic mechanism in the occurrence of the "rebound" contraction in this preparation. The present experiments did not provide any conclusive evidence for a splanchnic nervous control of the gastric vasculature.