Adverse effects of constitutively active alpha(1B)-adrenergic receptors after pressure overload in mouse hearts

Cardiac hypertrophy and function were studied 6 wk after constriction of the thoracic aorta (TAC) in transgenic (TG) mice expressing constitutively active mutant alpha(1B)-adrenergic receptors (ARs) in the heart. Hearts from sham-operated TG animals and nontransgenic littermates (WT) were similar in size, but hearts from TAC/TG mice were larger than those from TAC/WT mice, and atrial natriuretic peptide mRNA expression was also higher. Lung weight was markedly increased in TAC/TG animals, and the incidence of left atrial thrombus formation was significantly higher. Ventricular contractility in anesthetized animals, although it was increased in TAC/WT hearts, was unchanged in TAC/TG hearts, implying cardiac decompensation and progression to failure in TG mice. There was no increase in alpha(1A)-AR mRNA expression in TAC/WT hearts, and expression was significantly reduced in TAC/TG hearts. These findings show that cardiac expression of constitutively actively mutant alpha(1B)-ARs is detrimental in terms of hypertrophy and cardiac function after pressure overload and that increased alpha(1A)-AR mRNA expression is not a feature of the hypertrophic response in this murine model.