Capsaicin-sensitive sensory neurons regulate myocardial nitric oxide and cGMP signaling

We studied whether tissue levels of nitric oxide (NO) and cGMP are regulated by sensory nerves in normoxic and ischemic hearts. Wistar rats were treated with capsaicin to deplete neurotransmitters from capsaicin-sensitive sensory nerves. In separate experiments, capsaicin was applied perineurally to both vagus nerves for selective chemodenervation of vagal cardiac afferent nerves. Systemic capsaicin administration significantly decreased basal myocardial NO content assessed by electron spin resonance (ESR) spectroscopy, whereas, local treatment of vagus nerves did not change it. Both systemic and local capsaicin treatment decreased cardiac cGMP content measured by radioimmunoassay. In separate experiments, isolated hearts from control and systemic capsaicin-treated rats were subjected to 30-min global ischemia. NO signal intensity increased 10-fold after ischemia, whereas, cardiac cGMP decreased. Capsaicin pretreatment did not influence ischemic NO or cGMP content. These results suggest a major role for capsaicin-sensitive sensory neurons in the maintenance of basal but not ischemic myocardial NO and cGMP content. Vagal sensory nerves may be involved in the regulation of basal myocardial cGMP but not basal NO level. Consequently, basal NO content in the heart is regulated primarily by spinal afferent nerves.