Assessment of the nitric oxide system in the heart, aorta and kidney of aged Wistar-Kyoto and spontaneously hypertensive rats.

OBJECTIVE: To assess the nitric oxide (NO) system in the cardiovascular and renal systems of old Wistar-Kyoto (WKY) rats and old spontaneously hypertensive rats (SHR) compared with young rats of the same strains. DESIGN AND METHODS: The NO pathway was assessed: (i) in analytical studies measuring the concentration of nitrate in plasma and the activity of NO synthases in the left ventricle, renal cortex and renal medulla; and (ii) in functional studies, in which we measured the blood pressure effects of NO blockade with intravenous N-nitro-L-arginine methyl ester (L-NAME, 0.1 mg/kg) in anaesthetized rats. In addition, we studied NO production in the aorta comparing the force attained by isolated segments exposed to cumulative concentrations of L-NAME (10(-7)-10(-3) mol/l).
RESULTS: Plasma nitrate was significantly higher in old rats of both strains. Calcium-dependent NO synthase activity was markedly upregulated in the left ventricle, renal cortex and renal medulla of the old rats, both in hypertensive and normotensive animals. Intravenous L-NAME elicited deeper pressor effects in the old rats of either blood pressure condition. Aortic segments from old WKY rats, but not those from SHR, achieved remarkably stronger tension in response to L-NAME compared with the young counterparts.
CONCLUSIONS: These findings suggest that the NO system is upregulated in the cardiovascular system and the kidney in senescence, even in hypertension.