NOREPINEPHRINE-INDUCED CARDIAC-HYPERTROPHY OF THE CAT HEART

Norepinephrine administration causes progressive hypertrophy of the mammalian heart as measured by myocardial mass. The purpose of this study was to determine the growth response of the myocardial tissue components as well as the myocardial cell itself to norepinephrine. Young, adult cats were given low doses of norepinephrine in dextrose or dextrose alone twice daily for 15 days. On day 16, there were no changes in the animals body weight, right ventricular systolic pressure, right ventricular end-diastolic pressure, heart rate, cardiac index, or blood pressure. However, the right ventricle/body weight, the left ventricle/body weight and the total heart weight/body weight were increased significantly in the norepinephrine treated animals. The increase was on the order of 40%. The cardiac muscle cell was also significantly increased in size and both the right and left ventricular cardiac muscle cells exhibited a dramatic increase in size as measured by cross sectional area. Upon stereological examination it was found that the amount of hypertrophy as seen in the cardiac muscle cells was paralleled by the hypertrophy seen in the other tissue components of the myocardium. The volume density of the muscle cells, the interstitial components, as well as the blood vessel compartment were identical in the control and in the norepinephrine-treated groups. In conclusion, this study demonstrates that the response of the myocardium to norepinephrine is similar to that seen in response to a volume overload rather than that seen in response to pressure overload.