Rationale The intrinsic cardiac nervous system is important in our understanding of cardiac physiology. Using a pharmacological approach, we investigated the hypotheses that these nerves play a role in (1) direct ischaemic preconditioning (IPC) and (2) the cardioprotection offered by the humoral mediator of remote ischaemic conditioning (RIC).
Methods For the IPC experiment, isolated Langendorff perfused rat hearts were subjected to one of the following conditions; (1) Control + Hexamethonium (50 µM), (2) IPC (3 × 5-min global ischaemia) + Hexamethonium, (3) IPC alone. All hearts were subjected to 35-min ischaemia followed by 60-min reperfusion. In the second study, RIC (4 × 5 min hindlimb ischaemia/reperfusion) or sham was performed on anaesthetised rats, before exsanguination and centrifugation to obtain platelet-free plasma. After dialysis across a <12–14 kDa membrane, the dialysate was perfused through a naïve isolated Langendorff rat heart prior to an ischaemia-reperfusion injury, as described above. The hearts were assigned to the following groups; (1) Sham dialysate, (2) RIC dialysate, (3) Sham+hexamethonium (50 µM), (4) RIC+hexamethonium, (5) Sham+atropine (100 nM), (6) RIC+atropine (100 nM). All hearts were analysed for infarct size using triphenyl-tetrazolium chloride staining. Data presented as mean ± SEM and analysed using analysis of variance.
Results Hexamethonium partially, but significantly, abrogated IPC-mediated cardioprotection (Control = 44.4 ± 4.0%, IPC+Hex = 31.8 ± 5.0%, p < 0.05 vs IPC = 14.2 ± 1.9%). RIC dialysate significantly protected a naïve heart from injury (RIC = 27.6 ± 2.3 vs Control = 42.9 ± 1.2, p < 0.05). Both hexamethonium (45.8 ± 2.5%) and atropine (36.5 ± 3.4%) abrogated dialysate-mediated protection.
Conclusion Intrinsic cardiac nerves seem to be important in the induction of protection both in IPC and the response to the humoral RIC mediator.
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