Effect of triiodothyronine on renal growth and renal sodium reabsorption in hypothyroid rats

Abstract

Experiments were carried out to compare temporal changes in the paraaminohippuric acid clearance (C _PAH), renal sodium reabsorption ($R_{Na^ + }$), ribonucleic acid (RNA), and deoxyribonucleic acid (DNA) content in hypothyroid rats after a single injection of triiodothyronine (T₃) (50 μg/100 g body wt).C _PAH and$R_{Na^ + }$ showed no changes at 24 and 48 h. At 72 h, however, significant increases of 41% and 42% (per g kidney wet wt) were observed inC _PAH and$R_{Na^ + }$, respectively. The cortex in T₃-treated hypothyroid rats showed a significant increase in the protein/DNA and RNA/DNA ratios at 24 h and progressive increases to a level of 24%, and 37%, respectively, at 48 h. No changes in DNA content were observed at either time-points. The results show that the increases in RNA/DNA and protein/DNA ratios upon T₃ treatment preceded the increases inC _PAH and$R_{Na^ + }$, suggesting a direct effect of T₃ on renal cortical growth, rather than a secondary response to a primary increase in renal functions.