Sustained hyperosmolarity increses TGF-ß1 and Egr-1 expression in the rat renal medulla

Abstract Background Although TGF-s and the transcription factor Egr-1 play an important role in both kidney fibrosis and in response to acute changes of renal medullary osmolarity, their role under sustained hypo- or hyperosmolar conditions has not been elucidated. We investigated the effects of chronic hypertonicity and hypotonicity on the renal medullary TGF-s and Egr-1 expression. Methods Male adult Sprague Dawley rats ( n  = 6/group) were treated with 15 mg/day furosemide, or the rats were water restricted to 15 ml/200 g body weight per day. Control rats had free access to water and rodent chow. Kidneys were harvested after 5 days of treament. In cultured inner medullary collecting duct (IMCD) cells, osmolarity was increased from 330 mOsm to 900 mOsm over 6 days. Analyses were performed at 330, 600 and 900 mOsm. Results Urine osmolarity has not changed due to furosemide treatment but increased 2-fold after water restriction ( p p p p p p Conclusion We conclude that both TGF-s and Egr-1 are upregulated by sustained hyperosmolarity in the rat renal medulla, and it favors the expression of extracellular matrix components.