Abstract
Previous findings have shown that thyroid hormone markedly increases the speed of diastolic relaxation in the heart. This thyroid hormone-dependent change is also accompanied by an increased Ca2+ pumping ability in the sarcoplasmic reticulum. In an effort to determine the underlying cause of improved Ca2+ transport, mRNA levels of the slow Ca2+-ATPase of the sarcoplasmic reticulum were quantified on Northern blots. In hypothyroid rat hearts, the steady state level of Ca2+-ATPase mRNA was only 36% of control levels, whereas hyperthyroid rat heart mRNA levels were 136% of control. Ca2+-ATPase mRNA responded rapidly to T3, as the mRNA level was significantly increased by 2 h and normalized by 5 h after T3 injection into hypothyroid rats. The well established effect of thyroid hormone on improved myocardial contractility and increased speed of diastolic relaxation may in part relate to specific alterations in the level of the mRNA coding for Ca2+-ATPase, resulting in increased pump units.
Highlights
The cDNA encoding this enzyme has recently been cloned [6], and the availability of such a probe led us to investigate whether or not the previously published effects on activity might be due to increased numbers of pump units, reflected in changes of the specific mRNA
Ca2+-ATPasemRNA responded rap- status between the three groups was documented by comparison of idly to T3,as the mRNA level was significantly increased by2 h and normalizedby 5 h after T3 injection into hypothyroid rats
The well established effect of thyroid hormone on improved myocarcdoianltractility and increased speed of diastolic relaxation may in ventricle weight/body weight ratios (g/kg)
Summary
The cDNA encoding this enzyme has recently been cloned [6], and the availability of such a probe led us to investigate whether or not the previously published effects on activity might be due to increased numbers of pump units, reflected in changes of the specific mRNA. Alsot,he rapid effects of T3 on Ca2'-ATPasemRNAwere investigated to determine whether or not thyroid hormones regulate Ca2'-ATPase mRNA levels on a short termbasis. Previous findings have shown that thyroid hormone markedly increases the speed of diastolic relaxation iAnnimal Preparation-Male Spraque-Dawley rats were purchased the heart.
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