The effects of Nω-nitro-L-arginine methyl ester (L-NAME) were examined on pressor responses elicited by sympathetic nerve stimulation (SNS) in the pithed spontaneously hypertensive (SH) and Wistar-Kyoto (WKY) rats. Frequency-response curves (1-20 Hz) were carried out by using the pithing rod to stimulate the sympathetic chain. SNS produced an increase in the blood pressure of the pithed rats which was dependent on the frequency of the applied stimuli, however, a significantly greater increase was observed for the blood pressure of SH versus WKY rats. Bolus i.v. injections of L-NAME (0.03-1.0 mg/kg) augmented the increase in the blood pressure resulting from SNS. The potentiating effects of L-NAME displayed frequency as well as dose-dependency and the augmentation produced following the administration of L-NAME was greater in magnitude in the SH as compared to WKY rats. These differential effects of L-NAME in SH versus WKY rats suggest that the levels of L-arginine-derived nitric oxide are higher in the SH rats. Such an increase may reflect a compensatory response resulting from the elevated blood pressure of the SH rats.
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