Acute myocardial infarction inhibits the neurogenic tachycardic and vasopressor response in rats via presynaptic cannabinoid type 1 receptor.

The present study was carried out to examine whether acute experimental myocardial infarction affects the sympathetic transmission to vessels and the heart of pithed rats via a presynaptic mechanism and, if so, to check whether inhibitory presynaptic cannabinoid (CB) receptors and endocannabinoids are involved in this response. In pithed and vagotomized rats, electrical stimulation (0.75 Hz; 1 ms; 50 V; 5 or 15 pulses for increases in heart rate or blood pressure, respectively) of the preganglionic sympathetic nerve fibers or intravenous injection of isoprenaline (0.1 nmol/kg) or noradrenaline (1 nmol/kg) increased heart rate and blood pressure by approximately 50 beats/min and 40 mm Hg, respectively. Ligation of the left coronary artery reduced the electrically (as opposed to the chemically) induced tachycardic and pressor responses by approximately 30 to 40%. The inhibitory effect of myocardial infarction was prevented by the CB(1) receptor antagonist rimonabant but not by the CB(2) receptor antagonist N-[(1S)-endo-1,3,3-trimethyl-bicyclo[2.2.1]heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyra-zole-3-carboxamide (SR144528) and the transient receptor potential vanilloid 1 receptor antagonist capsazepine. The inhibitory effect of myocardial infarction was slightly enhanced by the inhibitors of anandamide and 2-arachidonyl glycerol degradation, 3'-(aminocarbonyl)[1,1'-biphenyl]-3-yl)-cyclohexylcarbamate (URB597) and 4-nitrophenyl-4-(dibenzo[d][1,3]dioxol-5-yl(hydroxy)methyl)piperidine-1-carboxylate (JZL184), respectively. Rimonabant increased myocardial infarction-induced mortality. Our results demonstrate that during the early phase of myocardial infarction the activation of presynaptic CB(1) receptors by endogenously formed cannabinoids contributes to the inhibition of the neurogenic tachycardic and vasopressor responses. Thus, the CB(1) receptor-mediated inhibition of excessive noradrenaline release from the sympathetic nerve fibers innervating the heart and vessels might play a protective role in myocardial ischemia.