Neuropeptide Y modulation of sympathetic activity in myocardial infarction.
OBJECTIVE
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 animal 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 infraction. 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 with 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.
Basu
S
S
Department of Anatomy, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
Sinha
S K
SK
Shao
Q
Q
Ganguly
P K
PK
Dhalla
N S
NS
D000818:Animals; D001345:Autoradiography; D008297:Male; D017551:Microdialysis; D009203:Myocardial Infarction / Q000503:physiopathology*; D009478:Neuropeptide Y / Q000502:physiology*; D009638:Norepinephrine / Q000096:biosynthesis; D010286:Paraventricular Hypothalamic Nucleus / Q000737:chemistry; D051381:Rats; D017207:Rats, Sprague-Dawley; D017476:Receptors, Neuropeptide Y / Q000032:analysis; D013564:Sympathetic Nervous System / Q000502:physiology*
D009478:Neuropeptide Y; D017476:Receptors, Neuropeptide Y; D009638:Norepinephrine