Role of Interstitial Angiotensin II and ATP in Mediating Renal Injury Induced by Recurrent Insulin Induced Hypoglycemia

Abstract

Aim: The present study hypothesizes that recurrent insulin induced hypoglycemia (RIIH) elevates renal interstitial ATP levels which in turn enhances AngII production. This interrupts the normal tubuloglomerular feedback (TGF) mechanism by stimulating afferent arteriolar vasoconstriction resulting in hypertension, which augments oxidative stress and could promote renal damage. Study Design: In the present study we adopted a microdialysis technique, which is a minimally invasive tool for monitoring chronic changes in renal interstitial fluid. Place and Duration of Study: Department of Basic Pharmaceutical Sciences, University of Louisiana at Monroe between September 2012 – October 2013. Methodology: Eight male Sprague Dawley rats (200-225 g) were anesthetized and microdialysis probes were inserted into their renal cortex. Post-surgery rats were treated with insulin (7U/kg body weight) for 2 weeks. Food and water intake were monitored daily. Physiological saline was perfused through the probe and dialysate was collected daily after insulin dosing and analyzed for ATP by luciferin-luciferase assay and AngII by EIA. At the end of the experiment, the hearts and kidneys were collected and analyzed for oxidative stress by EPR (Electron Paramagnetic Resonance) spectroscopy using CMH and CPH spin probes. Results: ATP and AngII levels were elevated from 31.65±4.4ng/µl (day 0) to 130.96±2.9 ng/µl (day 14) and 0.1±0.01 ng/ml (day 0) to 0.247±0.02 ng/ml(day 14), respectively. Elevation of peroxynitrite and superoxide anions were observed in the hearts and kidneys of insulin treated animals when compared to the control group. Conclusion: Thus the present study utilizes real-time chronic collections of renal interstitial samples to identify a potential mechanism where iatrogenic hypoglycemia promotes hypertension via a synergistic relationship between interstitial ATP, AngII and developed oxidative stress.