One of the major functions of the kidney is the transport of sodium and other solutes across the tubular epithelium. Generation of free radicals such as peroxyl, alkoxyl and aldehyde radicals can cause severe damage to the membrane bound enzymes such as Ca2+ ATPase, Mg2+ ATPase and Na+K+ ATPase (Pragasam et al., 2005).
Membrane Na+K+ ATPase play an important role in active transport of Na+ and K+ ions across the plasma membrane (Vani and Reddy, 2000). The enzyme Na+K+ ATPase utilizes the energy derived from ATP hydrolysis to pump out Na+ from inside the cell to transfer K+ from outside to cytosol. Its activity has been frequently used as a marker for plasma membranes and has been followed as a probe for monitering membrane integrity alteration in the physical state of various biological membranes (Stepherd, 1994).
Na+K+ ATPase activity markedly reduced in kidney and liver of ethylene glycol induced urolithic rats. This may be due to increased oxalate formation. Oxalate is known to interfere with a broad spectrum of solute transport processes in the renal tubule and inhibition of Na+K+ ATPase (Tulenko et al.,1988).
Ca2+ ATPase, the enzyme responsible for active calcium transport, is extremely sensitive to hydroperoxides and this may lead to its inhibition. Ca2+ ATPase activity was significantly lowered in the liver and kidney of ethylene glycol induced urolithic rats. The decreased activity of this enzyme may be due to the peroxide stress, which may act on the sulphhydryl groups present in the active sites of the Ca2+ ATPase (Srinivasan et al., 2004).
Mg2+ ATPase is to control the intracellular Mg2+ concentration which can modulate the activity of Mg2+ dependent enzymes and regulate rates of protein synthesis and cell growth (Sanu and Rubin, 1982). Ca2+ ATPase activity was significantly lowered in the kidney and liver of ethylene glycol induced urolithic rats. This may be due to free radical induced cell damage by oxalate and their severe cytotoxic effects, such as lipid peroxidation and protein oxidation in cell membrane followed by the alteration of the membrane fluidity, enzyme properties and ion transport.
Na+K+ ATPase, Mg2+ ATPase and Ca2+ ATPase in the plasma membrane keep the intracellular sodium low but intracellular magnesium and potassium high when compared with the levels in extracellular fluids (Pragasam and Kalaiselvi, 2005).
Our findings are in accordance with the studies of Prins et al. (2002) who showed that supplementation of L-arginine highly controlled the depletion of ATPase enzyme levels in tissues and restored the values to near normal levels in ethylene glycol treated rats.
Increased activities of serum and urine AST and ALT levels in ethylene glycol induced urolithic rats were observed. This can be attributed to the damaged structural integrity of the renal and hepatic cells causing the enzymes which are located in the cytoplasm to be released into the circulation (Senthilkumar et al.,2003).If membrane of other organelles such as mitochondria is damaged, soluble enzymes such as compartmentalized AST will also released. The release of these enzymes into the circulation will indicate both plasma and organelle membrane damage.
Reduced AST, ALT, ACP and ALP activities in renal and hepatic tissues of ethylene glycol induced urolithic rats was observed. This might be due to leakage of the enzyme into the general circulation from the collatered circulation. The stone formation may acclude the ureter, leading to an increase in back pressure in the renal pelvis and because of ischeamia, may ultimately damage the tubular cells (Thind and Nath 1978).
The above results are in agreement with the findings of Farooq et al. (2004), who reported that serum ACP and ALP levels were increased due to administration of oxalate and their levels were maintained near normal in phycocyanin supplementation.
Poonkuzhali et al. (1994) showed a decrease of kidney and liver marker enzymes and their restoration to near normal levels by uric acid administration to sodium glycolate fed urolithiatic rats. Similar results were also observed in our studies.