title: Role of thyroid hormone in regulation of renal phosphate transport in young and aged rats.
abstract: In the present study, we have examined the cellular mechanisms mediating the regulation of renal proximal tubular sodium-coupled inorganic phosphate (Na/Pi) transport by thyroid hormone (T3) in young and aged rats. Young hypothyroid rats showed a marked decrease in Na/Pi cotransport activity, which was associated with parallel decreases in type II Na/Pi cotransporter (NaPi-2) protein and messenger RNA (mRNA) abundance. In contrast, administration of long-term physiological and supraphysiological doses of T3 resulted in significant increases in Na/Pi cotransport activity, protein, and mRNA levels. Nuclear run-on experiments indicated that thyroid hormone regulates NaPi-2 mRNA levels by a transcriptional mechanism. In aged rats, although there were no changes in T3 serum levels (when compared with young animals), there were significant decreases in serum Pi concentration, renal Na/Pi cotransport activity, and NaPi-2 protein and mRNA abundance. These effects were mediated, at least in part, by a reduction in the transcriptional rate of the NaPi-2 gene, probably caused by, among other factors, a smaller response to the stimulatory action of T3. Compared with young rats, the old rats exhibited less sensitivity of the Na/Pi cotransporter to thyroid hormone, with-decreased effects in both hypothyroid (inhibitory) and hyperthyroid (stimulatory) animals.
authors: Department of Physiology, University of Zaragoza, Spain.
authors: A I
authors: AI
authors: Alcalde
authors: M
authors: M
authors: Sarasa
authors: D
authors: D
authors: Raldúa
authors: J
authors: J
authors: Aramayona
authors: R
authors: R
authors: Morales
authors: J
authors: J
authors: Biber
authors: H
authors: H
authors: Murer
authors: M
authors: M
authors: Levi
authors: V
authors: V
authors: Sorribas
mesh_terms: D000042:Absorption; D000375:Aging / Q000502:physiology*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D006980:Hyperthyroidism / Q000378:metabolism; D007037:Hypothyroidism / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000502:physiology*; D008297:Male; D010710:Phosphates / Q000097:blood / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D050608:Sodium-Phosphate Cotransporter Proteins; D050610:Sodium-Phosphate Cotransporter Proteins, Type II; D027981:Symporters; D013963:Thyroid Hormones / Q000502:physiology*; D014284:Triiodothyronine / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D010710:Phosphates; D012333:RNA, Messenger; D050608:Sodium-Phosphate Cotransporter Proteins; D050610:Sodium-Phosphate Cotransporter Proteins, Type II; D027981:Symporters; D013963:Thyroid Hormones; D014284:Triiodothyronine