Thyroid hormone control of Na+-K+-ATPase and K+-dependent phosphatase in rat heart.
To assess the possible role of the Na+ pump in mediating physiological responses to thyroid hormone in the rat myocardium, we examined the effects of L-3,5,3'-triiodothyronine (T3) on the activities of the closely associated enzymes, Na+-K+-dependent adenosine triphosphatase (Na-K-ATPase) and K+-dependent p-nitrophenyl phosphatase (K-dep-pNPPase). In hypothyroid rats, administration of T3 (50 microng/100 g body wt) resulted in significant increases (greater than 50%) in Na-K-ATPase and K-dep-pNPPase activities in both crude homogenates and microsomal fractions of the rat ventricle. Significant effects on Na-K-ATPase activity were also attained with low doses (1 microng/100 g body wt) of T3. A method was developed for assaying K-dep-pNPPase activity in cardiac slices. With this technique, enhancement in K-dep-pNPPase activity of 89.2% was found in ventricle slices after treatment of hypothyroid rats with T3 (50 microng/100 g body wt), implying that augmentation of the capacity of the Na+ pump is achieved in vivo. The potent analogue, L-3,5-diiodo-3' isopropyl thyronine (isopropyl T2) had the same effects on cardiac growth and Na-K-ATPase as T3, in hypothyroid rats. In contrast, the relatively inactive isomer, L-3,3',5'-triiodothyronine (reverse T3) had no significant effect on the heart weight-to-body weight ratio or on ventricular Na-K-ATPase activity.
D009597:4-Nitrophenylphosphatase / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D007037:Hypothyroidism / Q000201:enzymology; D008297:Male; D008861:Microsomes / Q000201:enzymology; D009206:Myocardium / Q000201:enzymology* / Q000648:ultrastructure; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D051381:Rats; D012964:Sodium / Q000378:metabolism; D013329:Structure-Activity Relationship; D013970:Thyronines / Q000031:analogs & derivatives / Q000494:pharmacology; D014284:Triiodothyronine / Q000494:pharmacology*
D013970:Thyronines; D014284:Triiodothyronine; D012964:Sodium; D010744:Phosphoric Monoester Hydrolases; D009597:4-Nitrophenylphosphatase; D000251:Adenosine Triphosphatases