The effects of clonidine on NOS inhibition induced hypertension, vascular alpha adrenoceptor sensitivity and plasma nitrite/nitrate levels in rats

ABSTRACTThe Effects of Clonidine on NOS Inhibition Induced Hypertension, Vascular AlphaAdrenoceptor Sensitivity and Plasma Nitrite/Nitrate Levels in RatsEffects of long-term clonidine administration on chronic NOS inhibition induced hypertensionand vascular α-adrenoceptor sensitivities remain to be elucidated. The aim of the presentstudy is to investigate mechanisms of NOS inhibition induced hypertension and effects ofclonidine on chronic NG-nitro-L-arginine (L-NNA) induced hypertension. All groups wereadministrated L-NNA and/or clonidine in two different concentrations for ten days. L-NNAwas administrated in concentration of 15 and 45 mg/100ml to dLNNA and yLNNA groups,respectively. Clonidine was also administrated in concentration of 150 and 225 g/100ml toKLO and yKLO groups, respectively. Blood pressure and heart rates were measured with tail-cuff method, plasma NOx levels with spectrophotometer. The α-adrenoceptor responses wereevaluated in toracic aorta rings in ?in vitro? conditions. Clonidine prevented the L-NNAinduced hypertension dose-dependently, but did not effect the heart rates decreased by L-NNA. The heart rates and blood pressure of normotensive rats were not changed by clonidinealone. Plasma NOx levels increased in dLNNA group but did not change in other groups. Thesensitivity of toracic aorta rings to phenylephrine and clonidine in yLNNA group andphenylephrine in dLNNA group increased. The sensitivity of toracic aorta rings tophenylephrine in yKLO group and to clonidine in KLO group increased. This study supportsthe idea suggesting that symphathetic nervous system activation is primarily responsible forthe chronic NOS inhibition induced hypertension. In conclusion, it was shown for first timethat clonidine prevented chronic NOS inhibition induced hypertension dose-dependently.. Key Words: Hypertension, Nitric Oxide, Clonidine, Alpha Adrenergic Receptors