Background The precise role of paracrine and autocrine factors in mechanical load-induced activation of cardiac gene expression is unknown. Here we report the effects of endothelin-1 (ET-1) and angiotensin II (Ang II) receptor antagonism on acute pressure overload-induced activation of cardiac B-type natriuretic peptide (BNP) gene expression in spontaneously hypertensive rats (SHRs) in vivo and on mechanical stretch-induced increase in atrial BNP gene expression it vitro. Methods and Results Acute pressure overload produced in conscious SHRs by infusion of arginine(8)-vasopressin (0.05 mu g . kg(-1) . min(-1)) for 2 hours resulted in an increase in BNP mRNA levels in the left ventricle as well as in the atrium. Bolus injections of bosentan (mixed ETA/ETB receptor antagonist, 10 mg/kg IV) but not losartan (AT(1) receptor antagonist, 10 mg/kg IV) blocked the increase of the BNP mRNA levels produced by pressure overload in the left atria, whereas the elevation of BNP mRNA levels was similar (a 1.9-fold increase) in the left ventricles of vehicle-, losartan-, and bosentan-infused SHRs. In an isolated perfused rat heart preparation, infusion of bosentan (1 mu mol/L) for 2 hours inhibited the mechanical stretch-induced increase in BNP mRNA levels in the right atria, whereas an AT(1) receptor antagonist, CV-11974 (10 nmol/L), had no effect. Conclusions The findings of the present study demonstrate that Ang II and ET-1 are not obligatorily required for stretch to trigger the increased BNP gene expression in ventricular myocytes invivo. In contrast, mechanical load on the atrial myocytes did initiate an ET-1-dependent expression of BNP gene showing that endogenous ET-1 production differentially regulates BNP gene expression in atrial and ventricular myocytes.
