THE EFFECTS OF ACUTE TEMPERATURE-CHANGE ON SMOOTH-MUSCLE CONTRACTILITY OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS WALBAUM) INTESTINE

The effects of altered temperature in vivo on in vitro smooth muscle c ontractility of rainbow trout intestine were investigated. Initial ana lysis of the data revealed a seasonal variation in the maximal tension of intestinal smooth muscle attainable with 5-hydroxytryptamine (sero tonin), carbachol, KCl, and transmural stimulation in vitro. Peaks occ urred in spring and troughs in autumn. There was no seasonal cycling o f the potency of the stimulants. All data regarding the efficacy of th e stimulants were subsequently corrected for seasonal variation. The r esponse of smooth muscle depends on the temperature of the water in wh ich the fish are placed (2-degrees-C-20-degrees-C). There was a marked linear increase in efficacy and a slight increase in potency of the s timulants with increasing temperature. Changes in responsiveness of th e intestinal smooth muscle occurred within 30 min of moving the fish b etween tanks. Smooth muscle reactivity returned to pretreatment values by 48h. Any changes in responsiveness with regards to time were unlik ely to be as a consequence of water temperature, but may have been a r esult of handling stress.