Study objectives: We compared the myocardial lesions caused by the long-term inhibition of nitric oxide (NO) biosynthesis with those associated with renovascular hypertension (two-kidney, one-clip model [2K-1C]) and superimposed streptozotocin-induced diabetes mellitus (DM).
Design: Prospective trial.
Setting: University laboratory.
Interventions: Male Wistar rats were classified into the following groups: (1) a control group; (2) the L-NAME group (treatment with the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester [L-NAME], 75 micro mol per rat per day, orally); (3) the 2K-1C group (renovascular hypertension); (4) the DM group (treatment with streptozotocin, 60 mg/kg via intraperitoneal route); and (5) the 2K-1C plus DM group (renovascular hypertension and streptozotocin-induced DM). Arterial BP was measured by a tail-cuff method for 3 weeks, after which histologic and stereological analysis of the heart was done and cardiac NO synthase type 3 (NOS3) levels were assessed by Western blotting. The circulating levels of nitrates/nitrites and thromboxane B(2) (TXB(2), the stable metabolite of thromboxane A(2)) were also measured.
Results: In DM and 2K-1C rats, the myocardial lesions consisted mainly of recent myocardial infarcts, which were more severe in the 2K-1C plus DM group. In L-NAME-treated rats, multiple foci of reparative fibrosis and fresh myocardial necrosis resembled the severe lesions found in the 2K-1C plus DM group. Although NOS3 protein expression increased (19 to 44%; p < 0.05) in all treated groups, serum nitrate/nitrite levels decreased only in the L-NAME group and the 2K-1C plus DM group. These two groups also showed a more pronounced increase in TXB(2) concentrations.
Conclusions: These results indicate that the association of hypertension and DM mimics the alterations induced by L-NAME in rats, which suggests a role for NO in the pathophysiology of hypertensive-diabetic cardiomyopathy.