Atrial natriuretic peptide secretion in rabbits with aortic regurgitation

Effects of methylprednisolone on hemodynamics and beta-adrenergic receptor signaling in rabbits with acute left ventricular failure

Studies suggest that corticosteroids may restore the responsiveness to catecholamines in hypotensive patients. Since the significance of this promising intervention in congestive heart failure remains to be explored, we determined the effects of methylprednisolone, a potent activator of beta-adrenergic receptor signaling, on hemodynamics and beta-adrenergic receptor regulation in an animal model of heart failure. Acute left ventricular overloading was produced by aortic regurgitation (AR) in 22 Japanese white rabbits. Eleven animals received an intravenous administration of methylprednisolone (AR + PSL), while 11 received saline (AR + C) for 1 week. A sham operation was performed on 10 other rabbits (S). There was no difference between the AR + C and AR + PSL groups in the decrease in aortic diastolic pressure immediately after the production of AR. The aortic diastolic pressure and regurgitant fractions were also similar in the two groups. The left ventricular end-diastolic and end-systolic dimensions were both larger, and the left ventricular end-diastolic pressure was higher in AR + C or AR + PSL than in S rabbits. Between the AR + C and AR + PSL, there were no differences in any of these variables. Cardiac output was lower in AR + C, but not in AR + PSL, than in S. Cardiac output in AR + PSL was significantly higher than in AR + C. The myocardial concentration of norepinephrine and the number of beta-adrenergic receptors were both lower in the AR + C and AR + PSL than in the S groups. The number of receptors in AR + PSL was higher than in AR + C. Maximal isoproterenol-stimulated adenylyl cyclase activity was similar in the AR + C and AR + PSL groups. Results suggest methylprednisolone yielded some benefits, including an increase in cardiac output and in total beta-adrenergic receptor number, in this animal model of heart failure.

Abnormalities in sympathoneuronal regulation are localized to failing myocardium in rabbit heart

OBJECTIVES

This study investigated the differences in sympathoneuronal regulation between acute left ventricular failure and chronic biventricular failure to determine whether an increase in plasma norepinephrine concentration plays a primary role in the genesis of the desensitization phenomenon in heart failure.

BACKGROUND

It remains to be determined whether plasma norepinephrine plays a primary role in the pathogenesis of sympathetic desensitization in heart failure in vivo.

METHODS

Acute left ventricular failure was induced by aortic regurgitation in seven rabbits. Chronic heart failure was induced by adriamycin treatment in another seven rabbits.

RESULTS

Cardiac output was lower in rabbits with aortic regurgitation than in seven sham-operated rabbits. Left ventricular end-diastolic pressure was higher in rabbits with aortic regurgitation, but no significant difference in right ventricular end-diastolic pressure was observed. Beta-adrenoceptor density and norepinephrine concentration in the left ventricular myocardium were lower in rabbits with aortic regurgitation; no such differences were observed for the right ventricular myocardium. Cardiac output was lower in adriamycin-treated rabbits than in seven control rabbits. Both left and right ventricular end-diastolic pressures were higher in experimental rabbits than in control rabbits. Myocardial beta-adrenoceptor density and norepinephrine content were reduced in both ventricles.

CONCLUSIONS

In chronic heart failure induced by adriamycin, sympathoneuronal activity was altered in both ventricles, whereas in acute left ventricular failure induced by aortic regurgitation, sympathoneuronal activity was affected only in the left ventricle despite a similar increase in plasma norepinephrine concentration in both animal models. Local abnormalities in sympathoneuronal regulation in failing myocardium therefore appear to be responsible for these phenomena.