Cold-acclimation leads to differential regulation of the steelhead trout (Oncorhynchus mykiss) coronary microcirculation.
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abstract
The regulation of vascular resistance in fishes has largely been studied using isolated large conductance vessels, yet changes in tissue perfusion/vascular resistance are primarily mediated by the dilation/constriction of small arterioles. Thus we adapted mammalian isolated microvessel techniques for use in fish and examined how several agents affected the tone/resistance of isolated coronary arterioles (<150 m ID) from steelhead trout (Oncorhynchus mykiss) acclimated to 1, 5, and 10C. At 10C, the vessels showed a concentration-dependent dilation to adenosine (ADE; 61 8%), sodium nitroprusside (SNP; 35 10%), and serotonin (SER; 27 2%) (all values maximum responses). A biphasic response (mild contraction then dilation) was observed in vessels exposed to increasing concentrations of epinephrine (EPI; 34 9% dilation) and norepinephrine (NE; 32 7% dilation), whereas the effect was less pronounced with bradykinin (BK; 12.5 3.5% constriction vs. 6 6% dilation). Finally, a mild constriction was observed after exposure to acetylcholine (ACh; 6.5 1.4%), while endothelin (ET)-1 caused a strong dose-dependent increase in tone (79 5% constriction). Acclimation temperature had varying effects on the responsiveness of vessels. The dilations induced by EPI, ADE, SER, and SNP were reduced/eliminated at 5C and/or 1C as compared with 10C. In contrast, acclimation to 5 and 1C increased the maximum constriction induced by ACh and the sensitivity of vessels to ET-1 (but not the maximum response) at 1C was greater. Acclimation temperature had no effect on the response to NE, and responsiveness to BK was variable.
