Lack of stimulation of kidney Na-K-ATPase by thyroid hormones in long-term thyroidectomized rabbits

The effects of long-term thyroidectomy and of subsequent triiodothyronine administration on kidney Na-K-ATPase were studied at the level of single nephron segments and were compared to the short-term effects previously reported. After 8-11 weeks, thyroidectomy resulted in a marked decrease in Na-K-ATPase activity in all the segments of the rabbit nephron, the proximal tubule, the thick ascending limb of Henle's loop, the distal convoluted tubule and the collecting tubule. Within this delay, thyroidectomy also decreased the ouabain-insensitive Mg-ATPase activity, the basal and hormone-stimulated adenylate-cyclase activity, and the volume of tubular epithelium in all the segments where these parameters were measured. Administration of 50 micrograms/kg body weight triiodothyronine to 8-11 weeks thyroidectomized rabbits did not restore Na-K-ATPase activity in any nephron segment within 48 h. These observations are different from those reported in animals thyroidectomized only 1 week before study since, within this latter delay, thyroidectomy altered specifically Na-K-ATPase activity, this action was observed on the proximal and collecting tubules exclusively and, triiodothyronine administration corrected Na-K-ATPase alterations after 48 h. Results of the present study indicate that in the long term, thyroidectomy has a wide spectrum of renal effects which involves the whole nephron and most cellular functions. The tubular involution induced by long-term thyroidectomy is probably responsible for the inability of kidney cells to quickly increase their Na-K-ATPase activity in response to hormonal stimulation.