Effect of thyroid hormone on the abundance of na, K-adenosine triphosphatase α-subunit messenger ribonucleic acid

The effects of thyroid hormone on Na, K-ATPase α-subunit mRNA (mRNA_α) content and Na, K-ATPase activity were measured in renal cortex, heart, and cerebrum of hypothyroid rats 24 and 72 h after injection of diluent or T₃. Use of a cDNA probe complementary to rat brain mRNA_α in Northern blot analysis revealed a single 26-27 S band in RNA isolated from these three tissues regardless of thyroid status. Tissue mRNA_α content was estimated by dot blot analysis of whole cell extracts and isolated total RNA. Injection of T₃ augmented mRNA_α content by 2.1- to 2.5-fold in kidney cortex and myocardium at 24 h. After three daily injections of T₃, the increases in mRNA_α were evident despite a global increase in RNA content associated with hypertrophy of these target tissues. Furthermore, the increases in abundance of mRNA_α after 72 h of T₃ treatment correlated with enhancement of Na, K-ATPase activity. In contrast, both mRNA_α and enzyme activity were invariant in the cerebrum. These data suggest that T₃-induced augmentation of Na, K-ATPase activity is mediated, at least in part, by increased mRNA_α content in target tissues.