Adenosine modulates cardiovascular functions through activation of extracellular signal-regulated kinases 1 and 2 and endothelial nitric oxide synthase in the nucleus tractus solitarii of rats.
BACKGROUND
The nucleus tractus solitarius (NTS) is the primary integrative center for baroreflex. Adenosine has been shown to play an important modulatory role in blood pressure control in the NTS. Our previous results demonstrated that adenosine decreases blood pressure, heart rate, and renal sympathetic nerve activity and modulates baroreflex responses in the NTS. We also demonstrated that a nitric oxide synthase (NOS) inhibitor may block the cardiovascular effects of adenosine in the NTS, which suggests interaction between the adenosine receptor and NOS. However, the signaling mechanisms of adenosine that induce nitric oxide release in the NTS remain uncertain. The aim of the present study was to investigate the possible signal pathways involved in the cardiovascular regulation of adenosine in the NTS.


RESULTS
Adenosine was microinjected into the NTS of urethane-anesthetized male Sprague-Dawley rats. Blood pressure and heart rate decreased significantly after microinjection. The cardiovascular effects of adenosine were attenuated by prior administration of the mitogen-activated protein kinase/extracellular signal-regulated kinase inhibitor PD98059 (6 nmol/60 nL) or an endothelial NOS-selective inhibitor, L-NIO (6 nmol/60 nL); however, the neuronal NOS-specific inhibitor vinyl-L-NIO (600 pmol/60 nL) did not attenuate the cardiovascular effects of adenosine. Western blot and immunohistochemistry studies demonstrated that adenosine induced extracellular signal-regulated kinases 1 and 2 and endothelial NOS phosphorylation in the NTS. Pretreatment with PD98059 diminished the endothelial NOS phosphorylation evoked by adenosine.


CONCLUSIONS
These results represent a novel finding that extracellular signal-regulated kinases 1 and 2 is involved in cardiovascular regulation in the NTS. They also indicate that the cardiovascular modulatory effects of adenosine in the NTS are accomplished by activation of mitogen-activated protein kinase/extracellular signal-regulated kinases 1 and 2 and then endothelial NOS.
Ho
Wen-Yu
WY
Graduate Institute of Medical Sciences, National Defense Medical Center, Taipei, Taiwan.
Lu
Pei-Jung
PJ
Hsiao
Michael
M
Hwang
Hwong-Ru
HR
Tseng
Yu-Chou
YC
Yen
Mao-Hsiung
MH
Tseng
Ching-Jiunn
CJ
D000241:Adenosine / Q000494:pharmacology / Q000502:physiology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002320:Cardiovascular Physiological Phenomena; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D017552:Solitary Nucleus / Q000378:metabolism*
D052250:Nitric Oxide Synthase Type III; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D000241:Adenosine