Cardiac function in juvenile salmon (<Emphasis Type="Italic">Salmo salar L</Emphasis>) in response to lipopolysaccharide (LPS) and inhibitors of inducible nitric oxide synthase (iNOS)

Salmon alevins responded to LPS with an initial increase in heart rate followed by a steady decrease over 2–3 days exposure and after 4 days heart rate had decreased significantly compared to control alevins. Effects of increasing concentrations of the inhibitor 1400W, which is highly specific for iNOS, were investigated in LPS exposed and control alevins. In alevins exposed to LPS for 4 days the heart rate increased a few seconds after addition of 1400W which was attributed to the vasoconstrictory effects of lowered levels of NO. In unexposed alevins application of the inhibitor 1400W resulted in decreased heart rate after about 30 min. A possible explanation for the decrease in heart rate resulting from an LPS challenge is that increased expression of iNOS produces increased NO levels and vasodilation. There is support for this idea since inhibition of iNOS using 1400W reverses this response. The results suggest that larval fish have at least some elements of a functional cytokine signalling system.