Kinin B2 receptor is not involved in enalapril-induced apoptosis and regression of hypertrophy in spontaneously hypertensive rat aorta: possible role of B1 receptor

Treatment with enalapril induces smooth muscle cell apoptosis and regression of aortic hypertrophy in spontaneously hypertensive rats (SHRs), whereas combined blockade of angiotensin II AT1 and AT2 receptors does not. We postulated that vascular apoptosis with enalapril involves enhanced half-life of bradykinin (BK) and kinin B2 receptor stimulation. SHR, 11-weeks old, were treated for 4 weeks with enalapril (30 mg kg−1 day−1), Hoe 140 (500 μg kg−1 day−1; B2 receptor antagonist), alone or in combination. Controls received vehicle. The half-life of hypotensive responses to intra-arterial bolus injections of BK were significantly increased in SHR anesthetized after 4 weeks of enalapril, an effect prevented by Hoe 140. The magnitude of BK-induced hypotension was significantly attenuated in all rats treated with Hoe 140. As compared to placebo, enalapril treatment significantly reduced blood pressure (−34±2%), aortic hypertrophy (−20±3%), hyperplasia (−37±5%) and DNA synthesis (−61±8%), while it increased aortic DNA fragmentation by two-fold. Hoe 140 given alone or in combination with enalapril affected none of these parameters. As a possible alternative mechanism, aortae isolated during the second week of enalapril treatment showed a transient upregulation of contractile responses to des-Arg9BK (EC50<1 nM), which were significantly reduced by [Leu8]des-Arg9BK (10 μM). Moreover, in vitro receptor autoradiography revealed an increase in expression of B1 and B2 receptor binding sites by 8–11 days of enalapril treatment. Aortic apoptosis induction and hypertrophy regression with enalapril do not involve kinin B2 receptors in SHR. Kinins acting via B1 receptors remains a candidate mechanism. Keywords: Hypertension, vascular hypertrophy, apoptosis, enalapril, kinin B2 receptor, kinin B1 receptor Introduction The development of hypertension is accompanied by cardiovascular hypertrophy and by enhanced growth of cardiac fibroblasts and vascular smooth muscle cells (SMCs) (Folkow, 1982; Lee et al., 1995; Hamet et al., 2001). In a genetic model of primary hypertension with low renin but high tissue angiotensin I-converting enzyme (ACE) levels, the spontaneously hypertensive rat (SHR), dysregulation of cell proliferation and death contributes to increased cardiovascular mass and DNA content (Walter & Hamet, 1986; Hamet et al., 1996; Thorin-Trescases et al., 2001). We previously reported that a transient burst of SMC apoptosis participates in the early phase of aortic mass regression in SHR treated with a variety of antihypertensive drugs (deBlois et al., 1997; Tea et al., 2000; Marchand et al., 2003). In losartan-treated SHR, onset regression of vascular hypertrophy is blocked by the coadministration of the caspase inhibitor z-VAD-fmk, suggesting an obligatory role for SMC apoptosis in this model of rapid vascular mass regulation (Marchand et al., 2003). The transient increase in vascular SMC apoptosis follows a time window that occurs within 1 week of treatment with AT1 receptor antagonists and around 2 weeks of treatment with an ACE inhibitor (ACEi) (deBlois et al., 1997; Tea et al., 2000). In contrast, blood pressure reduction follows a similar time course with both treatments. The different time course of apoptosis induction suggests that the underlying mechanisms differ for the two classes of drugs. We previously showed that regression of vascular mass and hyperplasia by valsartan is prevented completely by an antagonist of AT2 receptors (PD123319), suggesting the implication of this receptor in SMC apoptosis induced by AT1 receptor antagonists (Tea et al., 2000). Since ACEi reduces angiotensin II generation, this results in a reduced stimulation of AT1 and AT2 receptors. Since combined blockade of AT1 and AT2 receptors fails to induce vascular apoptosis in rats treated with valsartan+PD123319 for 2 weeks (Tea et al., 2000), these data further suggest a distinct pathway for ACEi and AT1 antagonists in regulating SMC apoptosis in this model. ACEi increases the half-life of kinins (Bhoola et al., 1992). Kinin B2 receptors contribute to the prevention of cardiovascular growth by ACEi in several models (Linz & Scholkens, 1992; Farhy et al., 1993; Linz et al., 1995; Benetos et al., 1997), although the role of kinins in regression of cardiovascular mass is less well defined (Black et al., 1996). The augmentation of bradykinin (BK) in the circulating levels could lead to apoptosis via the increased stimulation of B2 receptors and the subsequent increased release of nitric oxide, a known inducer of SMC apoptosis (Pollman et al., 1996; Ishigai et al., 1997). We therefore investigated the hypothesis that kinin B2 receptors are involved in the regression of aortic and cardiac DNA accumulation via apoptosis induced in SHR treated with enalapril.