AJP - Heart and Circulatory Physiology, Vol 253, Issue 2 341-H346, Copyright © 1987 by American Physiological Society
Effects of L-thyroxine in rats with chronic heart failure after myocardial infarction
R. Gay, T. A. Gustafson, S. Goldman and E. Morkin
The effects of thyroid hormone on left ventricular (LV) function and myosin
isoenzyme distribution were evaluated in rats 3 wk after myocardial
infarction. When compared with normal rats, animals selected for study had
moderately severe LV dysfunction as judged by decreased aortic and LV
systolic pressures and a 34% decrease in LV maximum rate of pressure
development (dP/dt). Average LV end-diastolic pressure was increased to 26
+/- 1 mmHg from 5 +/- 1 mmHg. The infarcted rats were divided into
saline-treated control (n = 10) and treatment (n = 13) groups. The latter
group received thyroxine (T4, 1.5 micrograms/100 g body wt) immediately
after the first determination of pressures and at 24 and 48 h. At 72 h,
aortic and LV pressures and myosin isoenzyme composition were measured. In
the thyroxine-treated group LV end-diastolic pressure decreased from 27 +/-
2 to 18 +/- 2 mmHg, and LV dP/dt increased from 5,627 +/- 249 to 6,064 +/-
355 mmHg/s. Heart rate and aortic pressure did not change. After saline
injections, LV end-diastolic pressure remained elevated, and the other
hemodynamic parameters were unchanged. Determination of ventricular myosin
isoenzyme composition in the saline-treated group revealed an increase in
the V3 myosin isoform and a decrease in the V1 isoform as compared with the
normal values. This pattern was not altered by T4 treatment. A separate
group (n = 7) of rats was treated with a 10 times larger dose of thyroxine
(15 micrograms/100 g body wt) for the same period of time. In this group,
there was neither hemodynamic improvement nor changes in myosin isoenzyme
distribution.(ABSTRACT TRUNCATED AT 250 WORDS)
