ROLE OF NITRIC OXIDE IN THE CONTROL OF BLOOD PRESSURE IN YOUNG AND ADULT SPONTANEOUSLY HYPERTENSIVE RATS

1. The depressor response to sodium nitroprusside (SNP) and the pressor response to N^ω‐nitro‐L‐arginine methyl ester (L‐NAME) were investigated in anaesthetized and ganglion‐blocked 6 week old (young) and 20 week old (adult) spontaneously hypertensive rats (SHR), and the results were compared with those in age‐matched normotensive Wistar‐Kyoto (WKY) rats. 2. SNP produced a dose‐dependent decrease of the mean blood pressure (BP) in both strains, and no differences in vascular sensitivity to SNP were observed between the strains. 3. L‐NAME caused dose‐dependent pressor responses in both strains. The sensitivity and the maximal response to L‐NAME in SHR were significantly greater than those in age‐matched WKY (P < 0.05 or 0.01; t‐test, 13d.f. in both ages). However, there were no significant differences in the responses between ages in each strain. 4. Acute reduction of BP induced by 7‐O‐ethylfangchinoline did not affect the responses to SNP and L‐NAME in the adult SHR. 5. These results indicate that a greater amount of NO is tonically released in SHR and that its contribution to BP control is greater in SHR than in WKY, whereas vascular sensitivity to NO does not differ between the strains. In addition, acute changes in BP do not affect the degree of dependency on NO for BP control.