Neuropeptide Y modulation of sympathetic activity in myocardial infarction

Objectives. We examined the possible effect of neuropeptide Y in modulating central sympathetic activity after myocardial infarction in rats. Background. Previous studies have shown the coexistence of neuropeptide Y and norepinephrine in the brain and a possible functional interaction between the two. Neuropeptide Y inhibits the release of norepinephrine at the presynaptic level and can be considered to act as a neuromodulator. Methods. Two groups of rats were examined in this study-an experimental group, defined as those rats undergoing left coronary artery ligation, and a sham group without coronary artery ligation, serving as the control group. The animals in both groups underwent microdialysis in the paraventricular nucleus at 2, 4 and 8 weeks after operation, Microdialysis samples were collected with and without injecting neuropeptide Y in the paraventricular nucleus. The concentration of norepinephrine was determined by injecting purified microdialysate samples during high performance liquid chromatography. To explore the receptor's possible role, autoradiographic localization of neuropeptide Y receptors in the paraventricular nucleus was also carried out in the experimental and sham groups. Results. The concentration of norepinephrine measured in the samples was decreased by 50% with neuropeptide Y in 2- and 4-week old rats after infarction, but by only 20% (p < 0.05) in 8-week old rats after infarction. The diminished inhibitory effects of neuropeptide Y on norepinephrine release was associated with increased sympathetic activity, as reflected by plasma norepinephrine; 8-week old rats after infarction had almost a 100% (p < 0.05) increase in their plasma norepinephrine level compared dth the sham group, Autoradiography revealed a significant decrease in density of neuropeptide Y receptors in the paraventricular nucleus in 8-week old rats after infarction (p < 0.05). Conclusions. The data presented in this report suggest that the reduction of the inhibitory activation of neuropeptide Y on sympathetic release may contribute to elevated norepinephrine levels after myocardial infarction.