Cannabinoids have recently been identified as cardioprotective agents (Lépicier et. al., 2003). However, the endocannabinoid, anandamide (AEA), was reported to be ineffective at reducing infarct size in rat isolated hearts subjected to ischaemia-reperfusion. In that study, AEA was dissolved in propylene glycol. Therefore, we tested whether anandamide, delivered in Tocrisolve100^TM (Tocris, UK), could reduce infarct size in a similar experimental model to the previous study.

Methods: Hearts taken from Male Wistar rats (250-350g) were perfused at a constant pressure (80 mmHg) and immersed in perfusate (Krebs bicarbonate solution + insulin, 100 mU.ml^-1) maintained at 37˚C. Electrical pacing was applied at 5 Hz during periods of perfusion. Left ventricular developed pressure (LVDP) was measured by means of a pressurised (5-10 mmHg) balloon inserted into the left ventricle and connected to a pressure transducer. Coronary flow (CF) was measured with a Transonic probe, placed between the perfusate reservoir and heart, connected to a T206 flow meter. Baseline mechanical function was recorded during an initial 15 min aerobic perfusion. Hearts were then subjected to 30 min of global, no-flow ischaemia followed by 2 h reperfusion and were electrically paced at 5 Hz whilst perfused. Infarct size (% of the left ventricle) was determined from triphenyltetrazolium chloride staining. Where used, SR141716A (SR6 CB₁ receptor antagonist, 1 µM) and SR144528 (SR8 CB₂ receptor antagonist, 1 µM) were present in the perfusate throughout the protocol. Vehicle (Tocrisolve100^TM + DMSO 0.1% vol.vol^-1, n = 9), AEA (1 µM, n = 7) or ACPA + JWH133 (1 µM each, n = 5) were infused 5 min prior to the onset of ischaemia and then throughout reperfusion. SR6 and SR8 were tested alone (n = 5 and 6, respectively) or in the presence of AEA (n = 6 and 6, respectively). Values (mean ± s.e.m) obtained after 2 h reperfusion were compared among the different experimental groups by analysis of variance supported by Dunnett’s post hoc test.

In vehicle-treated hearts, by the end of reperfusion, LVDP had recovered to 26±5% and coronary flow to 17±4% of baseline. Infarct size, measured at the end of reperfusion, was 21±3% of the left ventricle. AEA had no significant effect on recovery of LVDP or CF compared to control but significantly reduced infarction to 10±1% of the left ventricle. Alone, neither SR6 nor SR8 had any significant effect on infarct size (22±4% and 20±2% of the left ventricle respectively) or recovery of LVDP (24±4% and 28±5% of baseline, respectively) or CF (32±6% and 26±6% of baseline, respectively). However, both SR6 and SR8 blocked the reduction in infarct size induced by AEA (26±4% and 21±2% of the left ventricle, respectively), recoveries of LVDP and CF were not significantly affected. The combination of ACPA and JWH133 had no significant effect on the recovery of LVDP (10±1% of baseline) or CF (26±17% of baseline) or extent of infarction (19±5% of the left ventricle).

AEA delivered in Tocrisolve100^TM reduces infarct size when administered prior to ischaemia in rat isolated, Langendorff-perfused hearts. Activation of either CB₁ or CB₂ alone, or together, does not appear to account for cardioprotection induced by AEA.

Lépicier et al., (2003) Br J Pharmacol 139, 805-815