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Journal of Experimental Biology 163,33-48 (1992)
Published by Company of Biologists 1992

INTRINSIC MECHANISMS CONTROLLING CARDIAC STOMACH VOLUME OF THE RAINBOW TROUT (ONCORHYNCHUS MYKISS) FOLLOWING GASTRIC DISTENSION

DAVID J. GROVE ¹ and SUSANNE HOLMGREN ²

¹ Marine Science Laboratories Menai Bridge, LL59 5EY Wales, UK
² Comparative Neuroscience Unit, Department of Zoophysiology, University of Göteborg Box 250 59, S-400 31 Goteborg, Sweden

To whom reprint requests should be addressed

1. Inflation of the cardiac stomach of the rainbow trout induced reflex muscular contractions. The stomach then slowly relaxed asymptotically towards its maximum volume. Continued distension caused the stomach to become compliant and this was irreversible within the time course of each experiment (8h). Repeated periods of rest and distension revealed a short-term inhibition of reflex contractions which recovered as resting periods were extended. Sectioning the vagosympathetic trunk did not influence the response to distension. Similar responses occurred in isolated, perfused stomachs.

2. Both tetrodotoxin and atropine plus methysergide induced immediate compliance, suggesting that it was caused by the blockade of enteric excitatory neurones. Atropine alone primarily reduced reflex contractions whilst methysergide completed this suppression and induced profound gastric relaxation.

3. Somatostatin reversibly suppressed reflex contractions whilst vasoactive intestinal polypeptide (VIP) induced gastric relaxation.

4. A model is proposed in which distension initially causes reflex activity via cholinergic and serotonergic nerves, whilst gastric tone remains high. Somatostatin then suppresses rhythmic contractions, whilst VIP suppresses the tryptaminergic mechanisms that maintain gastric tone.

5. The rainbow trout stomach possesses intrinsic mechanisms that mimic the extrinsic, nerve-controlled ‘receptive relaxation’ or ‘accommodation’ that follows feeding in higher vertebrates.

Key words: teleost fish, gastric distension, somatostatin, vasoactive intestinal polypeptide, Oncorhynchus ntykiss, rainbow trout

Accepted on September 24, 1991