AJP - Heart and Circulatory Physiology, Vol 248, Issue 3 305-H310, Copyright © 1985 by American Physiological Society
Isomyosin and thyroid hormone levels in pressure-overloaded weanling and adult rat hearts
A. F. Martin, D. C. Robinson and R. T. Dowell
We examined the relationship between ventricular isomyosin composition and
plasma thyroxine (T4) 5 wk after partial constriction of the abdominal
aorta in weanling (21 day) and adult (8 wk) rats. Cardiac enlargement in
weanling aorta-constricted animals was associated with a significant (P
less than 0.001) decrease in %V1 isomyosin in both left (32%) and right
ventricles (25%) with a corresponding increase in the %V3 isomyosin and a
reduction in plasma T4 levels. However, the ratio of V1/T4 was similar in
weanling control (17.8 +/- 0.8) and aorta-constricted (18.0 +/- 1.4) rats.
In adult aorta-constricted animals, there was a significant (P less than
0.001) reduction in the %V1 (16%) isomyosin in the left ventricle and a
smaller decrease in the right ventricular V1 (8%) with no change in plasma
T4 levels. There was also a significant difference in V1/T4 between control
(16.1 +/- 0.4) and aorta-constricted (13.9 +/- 0.7) adult rats in contrast
to the maintenance of the V1/T4 in weanling aorta-constricted animals. Thus
both increased workload and changes in thyroxine levels contribute to the
isomyosin redistribution seen in weanling rats subjected to a pressure
overload, whereas, in adult hypertrophied hearts, alterations of the
ventricular isomyosin composition appear to be due solely to the increased
pressure overload.
