Abstract-B-type natriuretic peptide (BNP) plasma concentrations are raised in patients with heart failure. In several experimental models of cardiac overload, however, BNP mRNA and plasma BNP peptide levels are normal, despite the persistent increase in blood pressure and ventricular hypertrophy. In this study, the role of transcriptional mechanisms in the regulation of BNP gene expression were studied in angiotensin (Ang) II-induced hypertension by injecting DNA constructs containing the BNP promoter (Ϫ2200 to 75 bp of the transcriptional start site) linked to luciferase reporter into rat myocardium. Ang II was administered to conscious rats via intravenous infusion for 2 hours or by subcutaneous minipumps for 6 hours, 12 hours, 3 days, 1 week, and 2 weeks. Ang II increased blood pressure and cardiac mass and induced changes in diastolic function. The left ventricular BNP mRNA levels increased 2.2-fold (PϽ0.001) at 2 hours and peaked at 12 hours (5.2-fold, PϽ0.001). Thereafter, BNP mRNA levels decreased (1.8-fold induction at 3 days, PϽ0.05) and returned to control levels at 1 week, despite persistent hypertension and myocardial hypertrophy. Left ventricular BNP peptide concentrations followed the changes in BNP mRNA levels. The BNP promoter was activated 2.7-fold (PϽ0.05) at 2 hours and remained upregulated up to 2 weeks (2. The plasma concentration of BNP is raised in patients with cardiac disease, particularly those with heart failure. 3,4 BNP level is useful in the diagnosis of congestive heart failure 5 and may effectively guide treatment of patients in heart failure. 6,7 In experimental animal models, cardiac BNP gene expression increases rapidly in response to hemodynamic overload. 8 -10 However, controversy persists regarding to BNP gene expression in ventricular myocardium under normal conditions and in chronic cardiac overload. Indeed, conflicting studies both in the human and in animals describe either increased 9,11-14 or unchanged left ventricular BNP mRNA levels [15][16][17][18][19][20] in heart failure and hypertension. The reason for the normal BNP mRNA levels despite constant cardiac overload is not known but could result from transcriptional and/or translational mechanisms. To date, there are no reports on the molecular mechanisms responsible for regulating the BNP gene expression during cardiac overload in vivo.The aim of this study was to examine the effect of pressure overload on BNP gene expression and transcription in vivo.Hemodynamics, cardiac hypertrophy, systolic and diastolic function, left ventricular BNP mRNA and immunoreactive (ir)-BNP levels, and plasma ir-BNP concentrations were measured in rats infused with angiotensin (Ang) II for 2 hours, 6 hours, 12 hours, 3 days, 1 week, and 2 weeks. To measure the level of BNP gene transcription, DNA constructs containing the rat BNP promoter 2200 bp upstream of the transcription initiation site linked to a reporter gene 21 were injected into the left ventricular myocardium of rats. Finally, to explore further the possible mechanisms regu...

This study examined the role of angiotensin II in the increase of blood pressure, activation of cardiac natriuretic peptide gene expression, left ventricular hypertrophy, and vascular changes in nitric oxide-deficient hypertension. N(G)-nitro->L-arginine methyl ester (>L-NAME, 20 mg/kg/d), angiotensin II type 1 receptor (AT ) antagonist losartan (20 mg/kg/d), or their combination were administered orally for 8 weeks in Wistar rats. >L-NAME elevated systolic blood pressure, which reached its maximum within 4 weeks (200 +/- 4 mm Hg). Despite hypertension, >L-NAME administration for 8 weeks did not induce left ventricular hypertrophy. Losartan treatment significantly decreased the development of hypertension induced by >L-NAME and decreased left ventricular hypertrophy in untreated rats. In contrast, losartan did not prevent the hypertrophic remodeling of the mesenteric resistance arteries induced by >L-NAME. >L-NAME treatment increased ventricular atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) mRNA levels and immunoreactive BNP levels significantly. Losartan therapy decreased the >l-NAME-induced ventricular ANP gene expression by 69% (p < 0.05) and also reduced ventricular BNP mRNA levels so that it did not differ from control. Losartan treatment alone decreased ventricular immunoreactive ANP and BNP levels by 30% (p < 0.05). These results show that ventricular ANP and BNP gene expression are dissociated from the increased ventricular mass in nitric oxide deficiency-induced hypertension. Results suggest that >l-NAME-induced hypertension and the associated activation of ventricular ANP and BNP gene expression are, at least in part, mediated by angiotensin II, whereas the resistance vessel hypertrophy following nitric oxide synthase inhibition is angiotensin II independent.

The mechanisms mediating the activation of cardiac gene expression during pressure overload are not fully understood. We examined whether angiotensin II-induced activation of ventricular gene expression is related to blood pressure and ventricular mass or requires other factors by infusing angiotensin II in sham-operated and adrenalectomized rats. In sham-operated rats, angiotensin II (33 microg/kg x h, sc) produced a significant increase in mean arterial pressure (measured by telemetry) within 3 h. Mean arterial pressure (up to 45 h) and the increase in left ventricular hypertrophy in adrenalectomized rats during angiotensin II infusion were similar to those in sham-operated rats. Angiotensin II produced 3.6-fold (P < 0.01) and 20.4-fold (P < 0.001) increases in ventricular atrial natriuretic peptide mRNA levels at 12 and 72 h, respectively. Angiotensin II infusion for 12 h also significantly increased the ventricular mRNA levels of B-type natriuretic peptide (5.2-fold) and adrenomedullin (1.4-fold). Adrenalectomy either abolished (atrial natriuretic peptide and adrenomedullin) or blunted (B-type natriuretic peptide) the early activation of ventricular gene expression by angiotensin II. The baseline synthesis of atrial natriuretic peptide, B-type natriuretic peptide, and adrenomedullin in the ventricle remained unchanged in adrenalectomized rats. In conclusion, our results indicate that factors derived from the adrenals are required for angiotensin II-induced early activation of cardiac gene expression.