Stereological structural alterations of the heart and kidney were studied in four groups (n=5) of spontaneously hypertensive rats (SHRs) treated for 30 days: (i) control, (ii) NG-nitro-L-arginine methyl ester [L-NAME; nitric oxide (NO) synthesis inhibitor] alone, (iii) enalapril alone and (iv) L-NAME plus enalapril. Blood pressure (BP) was elevated significantly in NO-deficient SHRs (rats receiving L-NAME) or significantly lower in enalapril-treated SHRs. Co-administration of L-NAME and enalapril caused a 20% decrease in BP compared with untreated SHRs. NO-deficient SHRs had a decrease in body mass, but this loss of body mass was prevented efficiently in the enalapril-treated group. Enalapril treatment decreased the left ventricular (LV) mass index in SHRs, even in animals with NO synthesis blocked. NO deficiency in SHRs caused a larger decrease in the number of LV cardiomyocyte nuclei, which had a negative correlation with both LV mass index and BP. The volume-weighted glomerular volume (VWGV) separated the SHRs into two groupings: (i) control and NO-deficient SHRs, and (ii) enalapril- and L-NAME plus enalapril-treated SHRs. There was a significant difference between these two groupings, with VWGV being more than 15% smaller in the latter compared with the former grouping. The present findings reinforce the evidence that enalapril efficiently treats genetic hypertension, and demonstrate that this effect is observed even when NO synthesis is inhibited. Enalapril administration also decreases cardiac and renal structural damage caused by genetic hypertension, as well as by the interaction between genetic hypertension and NO deficiency.

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