Time course of AQP-2 and ENaC regulation in the kidney in response to PPAR agonists associated with marked edema in rats.
Peroxisome-proliferator-activated receptor (PPAR-gamma) agonists improve insulin sensitivity, but are associated with edema. Increased distal tubule sodium and water reabsorption through the epithelial sodium channel (ENaC) and aquaporin-2 (AQP-2) have been suggested to play mechanistic roles. To determine the molecular regulation of these proteins, we treated male, Sprague-Dawley rats daily by gavage with either vehicle, rosiglitazone (RGZ, 50mg/kg bw), or PD168 (a test compound causing marked edema, 10mg/kg bw), for 1, 3, or 5 days (n=6/treatment/time). On day 1, urine sodium excretion was significantly reduced by RGZ with a strong trend for PD168 (p-values 0.047 and 0.053, respectively) indicating early sodium retention. Blood pressure was lowered by RGZ- or PD168 treatment by 12h. Immunoblotting of whole kidney homogenates (WKHs) and a membrane-enriched fraction (MF) revealed increased band densities for AQP-2 in WKH (29 kDa and glycosylated bands) by both drugs at 1 day. However, at 5 days, the 29-kDa band was significantly decreased ( approximately 30% of vehicle). alpha-ENaC was increased by RGZ at 3 days; however both agents decreased alpha-ENaC by 5 days. In contrast, beta- and gamma-ENaC (85 kDa) were unchanged or decreased at all times by both agents. However, the 70-kDa band of gamma-ENaC (active band) in MF was increased in density (120-600%) by both agents on days 3-5. Overall, both agents resulted in early alterations in banding patterns for AQP-2 and ENaC subunits, many of which are described as activating changes. However, later reduction in AQP-2 and alpha-ENaC may represent an attempt to re-establish sodium and water balance.
Tiwari
Swasti
S
Division of Endocrinology and Metabolism, Department of Medicine, Georgetown University, Washington, DC 20007, USA. st285@georgetown.edu
Blasi
Eileen R
ER
Heyen
Jonathan R
JR
McHarg
Aileen D
AD
Ecelbarger
Carolyn M
CM
D052242:Adiponectin / Q000097:blood; D000818:Animals; D051399:Aquaporin 2 / Q000378:metabolism*; D001794:Blood Pressure / Q000187:drug effects; D004487:Edema / Q000139:chemically induced* / Q000378:metabolism*; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D007328:Insulin / Q000097:blood; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D009318:Natriuresis / Q000187:drug effects; D010080:Oxazoles / Q000633:toxicity*; D047495:PPAR gamma / Q000819:agonists*; D051381:Rats; D017207:Rats, Sprague-Dawley; D000077154:Rosiglitazone; D045162:Thiazolidinediones / Q000633:toxicity; D014230:Triazoles / Q000633:toxicity*; D014882:Water-Electrolyte Balance / Q000187:drug effects
D052242:Adiponectin; C496025:Aqp2 protein, rat; D051399:Aquaporin 2; D053503:Epithelial Sodium Channels; D007328:Insulin; D010080:Oxazoles; C532015:PD0344168; D047495:PPAR gamma; D045162:Thiazolidinediones; D014230:Triazoles; D000077154:Rosiglitazone