Role for sensory neuropeptides in aa-induced coronary vasodilation: a potential mechanism for 12-LOX-induced cardioprotection?

A.M. Goddard & A. Ahluwalia, Clinical Pharmacology, William Harvey Research Institute, Barts and The London, Charterhouse Sq., London EC1M 6BQ

Eicosanoids derived via the 12-lipoxygenase (12-LOX) pathway of arachidonic acid (AA) metabolism are protective against the damaging effects of myocardial ischaemia-reperfusion (I/R) injury, although the precise mechanism underlying this action remains to be elucidated. Our previous studies suggest that the non-selective cation channel TRPV1 expressed on cardiac sensory nerve endings may be involved in the cardioprotective actions of 12-LOX (McLean et al., 2002), therefore we sought to further investigate this possibility.

Male Wistar rats (250-350g) were heparinized, surgically anaesthetized, hearts rapidly excised and submerged in ice cold Krebs solution until they had stopped beating. Hearts were then mounted in the Langendorff mode and perfused with modified Krebs solution aerated with 95 % CO 2/5 % O2 at 37°C. Following a 15min equilibration, bradykinin (30pmol) and sodium nitroprusside (0.1nmol) were tested to determine endothelium-dependent and smooth muscle function, respectively. Vasodilator dose-response curves to AA (10-10– 10-6 mol) were constructed in hearts perfused with 12-LOX (2 μgml-1) in the absence and then presence of the non-selective LOX inhibitor nordihydroguaiaretic acid (NDGA; 10μM for 30min), the 12-LOX inhibitor baicalein (10μM for 30min), the neurokinin (NK)1 receptor antagonist SR140333 (1μM for 15min), the calcitonin gene-related peptide (CGRP) 1 receptor antagonist αCGRP8-37 (0.3μM for 20min) and the TRPV1 blocker capsazepine (3μM for 20 min). Responses to 12(S)-hydroperoxyeicosatetraenoic acid (12-HpETE; 10-20– 10-15 mol) were also compared after infusion of vehicle control or either capsazepine (3μM for 20min) or the TRPV1 agonist capsaicin (1μM for 20min, followed by 30min washout). All experiments were conducted in the presence of the cyclo-oxygenase inhibitor indomethacin (5 μM).

AA-induced vasodilation was mediated by a product of the 12-LOX pathway of AA metabolism since 12-HpETE also produced dose-dependent vasodilation (n=7), but also responses to AA were significantly reduced by NDGA (P<0.0001, n=5) and baicalein (P<0.0001, n=6). Sensory C-fibres were involved in vasodilator responses since desensitization of C-fibres with capsaicin (P<0.0001, n=5) almost abolished responses to 12-HpETE and responses to both AA and 12-HpETE were significantly attenuated by capsazepine (P<0.0001, n=5). Furthermore blockade of sensory fibre-derived neuropeptide receptors using SR140333 and αCGRP8-37 significantly reduced responses to AA (P<0.0001, ~60% suppression, n=6, and ~80% suppression, n=4, respectively).

In conclusion, our data demonstrate that AA and 12-HpETE-induced coronary vasodilation is mediated by activation of sensory TRPV1 causing release of vasoactive CGRP and substance P. Together these data highlight a novel pathway that may play a role in the cardioprotective actions of the 12-LOX pathway of AA metabolism.

McLean , P. et al. (2002) Circulation Research 90: 465-472

AG is supported by a BHF PhD studentship.