Renal Sodium-Glucose Cotransporter Activity and Aquaporin-2 Expression in Rat Kidney during Chronic Nitric Oxide Synthase Inhibition

Abstract

Background/Aims: The renal sodium glucose cotransporter (SGLT2) and the water channel aquaporin-2 (AQP2) play a critical role in tubular sodium and water reabsorption and in the regulation of extracellular fluid volume both in physiologic and pathophysiologic conditions. However, there is little information about SGLT2 and AQP2 expression and/or activity in hypertension and there are no reports during hypertension induced by chronic nitric oxide synthase (NOS) inhibition. Methods: Hypertension was induced in rats by oral administration of N^G-nitro-L-arginine methyl ester (L-NAME) (20 mg/kg/24 h) for 6 (H6) or 12 (H12) weeks. SGLT2 activity was measured using α-¹⁴C-methylglucose active uptake. The expression level of transporters was assessed by immunohistochemistry and/or immunoblotting. Results: SGLT2 activity was reduced in both H6 and H12; this was due neither to a decrease in SGLT2 expression nor to a change in membrane phospholipid composition. In H6, AQP2 expression diminished only in the inner medulla (IM), while in H12 it diminished in both outer (OM) and IM. This reduced expression of AQP2 may partially account for the increased urinary volume and decreased urinary osmolality in H12, since we obtained a strong correlation between AQP2 expression and these urinary parameters in both OM and IM. Conclusion: We propose that in rats in which hypertension is induced by NOS inhibition, SGLT2 activity and AQP2 expression are modified to compensate for the elevated arterial pressure. However, we cannot discount the possibility that the observed changes are due to the decrease in NO production itself.

Renal Response to L-Arginine in Diabetic Rats. A Possible Link between Nitric Oxide System and Aquaporin-2

“…This is in accordance with a previous work of our laboratory, where we showed that AQP2 is down regulated in the renal medulla of rats made hypertensive by chronic inhibition of NOS [27]. Besides, we have recently demonstrated a synergistic effect of NO and NFATc (nuclear factor of activated T cells) promoting an increase in AQP2 mRNA and protein in mouse papilla and activation of the AQP2 promoter in kidney-derived cells [47].…”

“…Animals were allowed to acclimatize to metabolic cages for two days and then fasted for 24 h before the collection of urine to avoid differences in plasma glucose concentration and NOx excretion due to different food intake. Urine samples (24 h) were analyzed for total protein by a turbidimetric method using trichloroacetic acid as previously described [27]. Urine analysis for glucose and ketones was carried out using reactive strips (Keto-Diastix Bayer Diagnostics S.A., Argentina).…”

Expression and Activity of SGLT2 in Diabetes Induced by Streptozotocin: Relationship with the Lipid Environment

“…Animals were left to acclimatize to the metabolic cages for 2 days before the urine collection. Urine samples (24 h) were analyzed for urinary protein excretion (U p ) by a turbidimetric method using trichloroacetic acid [18] as previously described [19]. Urine analysis for urinary ketone excretion (U ketones ) was undertaken using a nitroprusside test (Keto-Diastix Bayer Diagnostics S.A., Buenos Aires, Argentina).…”

“…BBV from rat renal cortex were prepared by MgCl 2 precipitation and differential centrifugation as previously described [19]. The enrichment in BBV was determined previously by the increase in brush border markers such as γ-glutamyl transferase activity and sphingomyelin (SM) [20].…”

“…Immunoblotting analysis was used to identify SGLT2 and beta-actin in BBVs as previously described [19]. Blots were incubated overnight at 4°C with SGLT2 antibody (Alpha Diagnostic International, San Antonio, Tex., USA) diluted in blocking solution (1:1,000) and beta-actin antibody (1:3,000; Chemicon International, USA).…”