Abstract 223: Genetic Deletion or Pharmacological Blockade of Ddah-1 Impairs Reabsorption of Fluid From the Rat Renal Proximal Tubule Perfused in vivo.
Nitric oxide (NO) stimulates proximal tubule (PT) Na+ and fluid reabsorption. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase (NOS) but its effects on tubular function are unknown. ADMA is metabolized by dimethylarginine dimethylaminohydrolase (DDAH) whose type 1 isoform is predominant in the PT. SNIPs of DDAH-1 predicted the rate of decline of renal function in patients with chronic kidney disease (CKD). Therefore, we tested the hypothesis that DDAH-1 metabolizes ADMA in the proximal tubule and thereby enhances PT fluid reabsorption (Jv). Jv was measured in anesthetized rats by direct in vivo microperfusion and recollection of artificial tubular fluid (ATF) in S2 segments of the PT isolated between oil blocks. Addition of a selective inhibitor of DDAH-1, L-257 (10-4M) to ATF did not effect Jv when compared to addition of vehicle (3.40.6 vs 3.10.3 nl/min/mm). However, L-257 administered as a bolus intravenous injection (60mg/kg) 2hrs before microperfusion of the PT with L-257 significantly reduced Jv to 1.80.2 nl/min/mm, (P<0.05) and significantly enhanced urine flow rate (2.1±0.3 vs 9.0±1.8 μl/min; P<0.05). Microperfusion of ADMA (10-4 M) or L-NAME (10-4 M) into the PT both reduced Jv significantly to 2.00.2 and 1.80.2 nl/min/mm, respectively (P<0.05). Rats pretreated with a rapid intravenous injection of siRNA targeted to DDAH-1 that reduced its renal mRNA expression significantly also had reduced Jv (3.1±0.2 vs 2.2±6.2 nl/min/mm; P<0.05) and had a further reduction in Jv with 10-4M ADMA added to ATF to 1.4±0.1 nl/min/mm; (P<0.005). In conclusion, PT fluid reabsorption is regulated by ADMA and its tubular metabolism by DDAH-1. The two hour delay in the effects of a bolus injection of L-257 to diminish Jv indicated the time required after inhibition of DDAH-1 for accumulation of sufficient tubular ADMA to impair PT reabsorption. Thus, L-257 is a novel regulator of PT function and is a proximal tubule diuretic. SNIPs that alter DDAH-1 in the PT may change renal function and contribute to CKD progression.
- © 2012 by American Heart Association, Inc.