Anybody have an idea why these two studies conflict with each other?
In the first study it suggest that arginine fed to rats at 2% in diet induces renal failure but the second study says no adverse effect in rats fed up to 5% arginine in diet.
http://www.ncbi.nlm....pubmed/12670191
influence of green tea polyphenol in rats with arginine-induced renal failure.
Abstract
To determine whether green tea polyphenol ameliorates the pathological conditions induced by excessive dietary arginine, green tea polyphenol was administered to rats at a daily dose of 50 or 100 mg/kg body weight for 30 days with a 2% w/w arginine diet. In arginine-fed control rats, urinary and/or serum levels of guanidino compounds, nitric oxide (NO), urea, protein, and glucose increased significantly, while the renal activities of the oxygen species-scavenging enzymes superoxide dismutase (SOD) and catalase decreased, compared with casein-fed rats. However, rats given green tea polyphenol showed significant and dose-dependent decreases in serum levels of creatinine (Cr) and urea nitrogen and urinary excretion of Cr, and they exerted a slight reduction of nitrite plus nitrate, indicating that green tea polyphenol reduced the production of uremic toxins and NO. In addition, in arginine-fed rats the urinary urea, protein, and glucose level increases were reversed by the administration of green tea polyphenol. Moreover, in rats given green tea polyphenol the SOD and catalase activities suppressed by excessive arginine administration increased dose-dependently, implying the biological defense system was augmented as a result of free radical scavenging. These results suggest that green tea polyphenol would ameliorate renal failure induced by excessive dietary arginine by decreasing uremic toxin, and NO production and increasing radical-scavenging enzyme activity.
http://www.ncbi.nlm....pubmed/15204729
Thirteen-week oral toxicity study of L-arginine in rats.
Abstract
The amino acid L-arginine (Arg) has been used extensively in dietary and pharmacological products. This study evaluated toxicological and behavioral effects of Arg produced by Ajinomoto Co. (Tokyo, Japan) during a dosing study with male and female Sprague-Dawley rats. The amino acid was incorporated into a standard diet at doses equal to 1.25%, 2.5%, and 5.0% (w/w). A control group of rats received only a standard diet. All diets were administered ad libitum for 13 continuous weeks. To examine recoverability of any potential effects, the administration period was followed by a 5-week-long recovery, during which only a standard diet was provided. In male and female rats in each concentration group, treatment-related changes were not observed for clinical signs, body weights, diet consumption, ophthalmology, gross pathology, organ weight, or histopathology. An elevated level of plasma glucose was detected in some male rats (5.0%, w/w) during the analysis conducted in the fifth week of administration; however, the degree of the change was within the physiological range, and no changes were observed at the end of the administration period. In the same group, an increase in hemoglobin, together with a tendency toward an increase in the red blood cell counts, was found, but the change was considered toxicologically insignificant. The no-observed-adverse-effect level (NOAEL) for Arg was estimated at 5.0% (w/w) for both genders (males, 3.3 +/- 0.1 g/kg/day; females, 3.9 +/- 0.2 g/kg/day).
They didn't say they actually induced any renal failures in the 1st study. They only talk about measuring increased nitric oxide (NO), urea, protein, and glucose, which are believed to be markers associated with renal failure, and note a decline in those levels when polyphenols are also taken. They therefore inferred a lower risk of renal failure. Also, the 1st study's abstract doesn't specify when they took their measurements... my guess is they did it right at the end of the 30 day test period. In the 2nd study they focused on marker recovery and measured 5 weeks after 13 weeks of test dosages ended. So the studies would not contradict each other unless they also waited 5 weeks in 1st study to take measurements. Which I doubt is the case.
It is curious that they did not measure blood pressure, which is probably the biggest risk factor for renal failure. Increased NO production lowers high blood pressure. I assume the green tea polyphenol plus arginine test group would have had increased blood pressure compared to the arginine-only group. Which would undercut the inference drawn in the 1st study.
The biggest thing I get from the 1st study is that green tea polyphenols probably neutralize the effects of arginine so it would probably be a waste to take them together. What I do is cycle my arginine and polyphenols (with antioxidants) on alternate weeks. Also note the arginine dosage they used for the 5% case translates to 3.3 g/kg of rat body weight daily suggesting the 2% case translates to about 1.32 g/kg rats or 220 mg/kg humans assuming a 6:1 rat to human conversion ratio. Which would be over 15 grams per day for a 70 kg human male.
Howard
