Influence of thyroid hormone on (Na+ + K+)-dependent adenosine triphosphatase activity in rat submandibular glands.

Surgical thyroidectomy decreased (Na+ + K+)-dependent adenosine triphosphatase (Na-K-ATPase) activity in rat submandibular glands. Three successive doses of triiodothyronine (100 microgram/100 g of body wt) to euthyroid and hypothyroid rats produced 24 and 23 per cent increase in the enzyme activity, compared to control values. When hypothyroid rats were given smaller doses of triiodothyronine (4 microgram/100 g body wt every 48 h) for 27 days, Na-K-ATPase activity increased 40 per cent over the corresponding values in the control hypothyroid rats. Thus, thyroid hormone acts on rat submandibular glands to increase the Na-K-ATPase activity of that target tissue.