CHANGES IN SMOOTH-MUSCLE CONTRACTILITY OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS WALBAUM) INTESTINE DURING ACCLIMATION TO ALTERED TEMPERATURE

The effects of altered water temperature in vivo on in vitro smooth mu scle contractility of rainbow trout intestine were investigated. Tempe rature has a significant effect on receptor-mediated intestinal smooth muscle contractility in the rainbow trout. The efficacy of 5-HT, carb achol, and transmural stimulation increased with temperatures above 10 -degrees-C, with an optimal increase at 15-degrees-C. There was also a modest increase in the potency of 5-HT and carbachol within 2 days of establishing trout at 20-degrees-C. By day 8, most of these changes h ad either stabilized or were returning to control values, suggesting t hat acclimation changes in membranes and enzyme activities were taking effect. However, the contractile responses to carbachol and transmura l stimulation were still increasing at this time. This may imply that the muscarinic receptors are more resistant to membrane acclimation ch anges and may take longer to adapt. Because these experiments were con trolled for handling stress and seasonal changes that affect contracti lity, we have been able to demonstrate some early changes in smooth mu scle contractility that occur during acclimation to altered temperatur e.