Noradrenaline turnover and metabolism in myocardium following aortic constriction in rats.

STUDY OBJECTIVE

The aim was to provide meaningful information on the function of the sympathetic system soon after an increased pressure overload on the heart.

DESIGN

Noradrenaline storage, turnover, uptake, and synthesis were investigated at 3, 14, and 28 d after aortic banding in rats. Sham operated rats without aortic banding were used as control group.

EXPERIMENTAL MATERIAL

Left ventricle, spleen, and kidney from male Sprague-Dawley rats (175-200 g) were used in this study.

MEASUREMENTS AND MAIN RESULTS

Cardiac noradrenaline concentration was decreased at 3 d and 28 d after banding and increased at 14 d; left ventricular mass was increased from 14 d onwards. The rate of change in the specific activity of myocardial noradrenaline (noradrenaline turnover) as well as dopamine beta hydroxylase, an enzyme for noradrenaline synthesis, was unaltered at 3 d, increased at 14 d, and decreased at 28 d after aortic banding. Myocardial [3H]noradrenaline uptake, on the other hand, was decreased at all time points studied. The changes observed in the myocardium at day 14 were specific since noradrenaline turnover rate was unaltered in other peripheral organs such as spleen and kidney. Furthermore, after ganglionic blockade with pentolinium, both sham operated control and banded animals had identical, low noradrenaline turnover rate constants, and significant restoration of cardiac weight and noradrenaline stores was observed in the hearts from banded animals.

CONCLUSIONS

Noradrenaline turnover and metabolism are altered soon after imposing increased workload on heart. Whether or not the changes in the sympathetic activity are a prerequisites for hypertrophy still remains to be seen.