AJP - Heart and Circulatory Physiology, Vol 250, Issue 5 861-H865, Copyright © 1986 by American Physiological Society
Thyroidectomy of SHR: effects on ventricular relaxation and on SR calcium uptake activity
R. L. Rodgers, S. Black, S. Katz and J. H. McNeill
Ventricular hypertrophy and hypothyroidism are each characterized by
impaired cardiac muscle relaxation and sarcoplasmic reticulum (SR) calcium
uptake activity. A previous report also showed that hypothyroidism does not
reverse ventricular hypertrophy (left-to-right ventricular weight ratios)
of spontaneously hypertensive rats (SHR). We characterized the effects of
thyroidectomy of 8 wk duration on relaxation of ejecting hearts and on SR
calcium uptake activity from SHR and nonhypertrophic Wistar-Kyoto rat (WKY)
controls. Relaxation was quantified by plotting maximum left ventricular
pulse pressure (Pmax) vs. the area under the falling phase of the left
ventricular pressure wave at three different pressure loads. Ventricles of
euthyroid SHR were characterized by impaired relaxation and depressed SR
calcium uptake activity compared with those of euthyroid WKY, confirming
earlier studies. Thyroidectomy reduced ventricular relaxation and SR
calcium uptake activities to about the same extent in SHR and WKY strains
so that these measurements were most depressed in the SHR hypothyroid
group. When all groups were considered, the extent of mechanical relaxation
ex vivo and the rate of SR calcium uptake in vitro were well correlated.
