Effects of N-G-nitro-L-arginine on the blood pressure of spontaneously hypertensive rats with different degrees of hypertension

The effects of NG-nitro-L-arginine (L-NNA) on blood pressure of various str ains of spontaneously hypertensive rats were studied. Blood pressure of the rats was higher in the order of WKY, SHR, SHRSP, M-SHRSP. L-NNA caused an elevation of the blood pressure, which was greatest in SHR and smallest in WKY and M-SHRSP. Endothelium-dependent relaxation of aortae by acetylcholin e was greatest in preparations from WKY and it decreased as the blood press ure of rats increased. Phenylephrine (higher than 10(-6) mg/kg) caused an e levation of the blood pressure, which was greatest in SHR and smallest in M -SHRSP. It was suggested that L-NNA elevated blood pressure by inhibiting t he basal or flow-induced release of nitric oxide from the endothelium that is causing a reduction in vascular smooth muscle tone. The smaller effect o f L-NNA in WKY was due to weak smooth muscle tone, while the smaller effect in SHRSP and M-SHRSP is due to impaired function of endothelium.