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Control of the steelhead trout (Oncorhynchus mykiss) coronary microcirculation: Temperature effects and role of the endothelium

The effect of temperature on the local control of microvessel resistance in fish is poorly understood, plus the influence of prostaglandins (PG) and nitric oxide (NO) on vascular smooth muscle in these taxa is controversial. Thus, we measured the dose‐dependent responses of isolated coronary microvessels (< 150μm diameter) from 10, 5 and 1°C acclimated trout to several vasoactive compounds. While vessel sensitivity to most compounds was reduced at 1°C, cold exposure altered the response of vessels to low acetylcholine concentrations and increased the sensitivity of vessels to endothelin‐1. We also found that the dosedependent dilation caused by the endothelium dependent Ca2+ ionophore A23187 was abolished by indomethacin (Indo) and L‐NIO, cyclooxygenase and NO synthase inhibitors, respectively. This suggests a possible role for both PG and NO pathways in endothelial derived regulation of vascular resistance in this tissue. Finally, interleukin (IL)‐1β is linked with hypotension and cardiovascular collapse in mammals during heatstroke, and may have similar effects in fish. Isolated trout coronary vessels showed a dose‐dependent dilation to recombinant (r) IL‐1β that was not affected by an acute increase in temperature of 10 to 20°C. Moreover, the effect of rIL‐1β appears to be endothelium dependent and involve a PG pathway (vessel denudation and Indo both inhibited the rIL‐1β effect). Funding by NSERC & FCT.