Effects of 5-hydroxytryptamine on reperfusion injury in rat isolated heart and left atrium

Sian E James, Sally Coleman, Gary F Baxter. Cardiff University, Cardiff, United Kingdom.

Background: In acute coronary syndromes 5-hydroxytryptamine (5-HT) is released from platelet granules. Preliminary data suggests platelet and neuronal derived 5-HT may also exert autocrine/paracrine effects in the myocardium. There are reports that 5-HT triggers post-ischaemic contractile dysfunction and apoptosis (Rajesh et al, 2006). However more recent reports suggest that 5-HT can protect myocardium against ischaemia-reperfusion injury (Takano et al, 2004). The aim of this study was to examine the effects of 5-HT on infarct size following regional ischaemia and reperfusion in the isolated rat heart and on recovery of contractile function following simulated ischaemia of the left atria. We hypothesised that 5-HT can limit reperfusion injury in a concentration-dependant manner. Methods for isolated heart: Rats were anaesthetised with sodium pentobarbital and hearts excised for Langendorff perfusion with Krebs’ buffer. After stabilisation, hearts were subjected to 35 minutes of left coronary artery occlusion and 120 minutes of reperfusion, following which infarct size was determined by tetrazolium staining. 5-HT perfusion (50nM, 1μM, 10μM or 30μM) was commenced 5 minutes prior to reperfusion and continued until 10 minutes after reperfusion. Infarct size was expressed as a percentage of the ischaemic risk zone. Statistical comparison was made with ANOVA followed by Newman-Keuls multiple comparison post-hoc test, with a p-value<0.05 considered statistically significant. Methods for isolated left atria: Left atria were dissected from the isolated perfused hearts and mounted in an organ bath superfused with Krebs’ buffer, connected to an isometric transducer (resting tension, 0.5g) and electrically paced (2 Hz). Reoxygenation was for 60 minutes. Ischaemia was simulated by use of a glucose-free Kreb’s solution and gassing with 95% N2 for 45 minutes. 5-HT (50nM, 100nM and 1μM) was added to the bath at reoxygenation until wash out 15 minutes later. Statistical comparison was made with repeated measures ANOVA followed by Dunnett’s post-hoc test, with a p-value<0.05 considered statistically significant. Results for isolated heart: Control infarct size (% of ischaemic risk zone) was 60.8 ± 8.4%. The administration of 50nM 5-HT at reperfusion induced a significant limitation of infarct size (31.5 ± 4.5% p<0.05 vs. control). 5-HT at higher concentration also reduced infarct size but this did not reach statistically significance. Results for isolated left atria: 5-HT 1μM increased the developed tension in reoxygenation, with developed tension at 60 minutes being 47.0 ± 10.6%, (% baseline ± SEM) vs control of 38.9 ± 14.2%. 5-HT applied to normoxic left atria had no effect on contractile function at any concentration used. Conclusion: These findings support 5-HT having a cardioprotective action against reperfusion injury, which is independent of an inotropic effect. Further work will establish the mechanism of action of 5-HT by which this occurs.

Rajesh, K.G. et al (2006). 5-HT2 receptor blocker sarpogrelate prevents downregulation of antiapoptotic protein Bcl-2 and protects the heart against ischemia-reperfusion injury. Life Sci 79: 1749-1755.
Takano, S. et al (2004). Dual roles of 5-hydroxytryptamine in ischemia-reperfusion injury in isolated rat hearts. J Cardiovasc Pharmacol Ther 9: 43-50.