Melatonin, the chief secretory product of the pineal gland, is a direct
free radical scavenger. In addition to a direct scavenging effect on
nitric oxide (NO), its inhibitory effect on
nitric oxide synthase (NOS) activity has been also reported.
L-arginine is the substrate for both NOS and
arginase. It has been suggested that there is a competition between
arginase and NOS and that they control each other's level. NO plays a crucial role in the pathogenesis of myoglobinuric
acute renal failure (ARF). In this study, the authors aimed to investigate the effect of
melatonin on
arginase activity,
ornithine, and NO levels on the myoglobinuric ARF formed by intramuscular (i.m.) injection of hypertonic
glycerol. Forty rats were randomly divided into four groups. Rats in
SHAM were given saline, and those in groups ARF, ARF-M5, and ARF-M10 were injected with
glycerol (10 mL/kg) i.m. Concomitant and 24 hours after
glycerol injection for the ARF-M5 and ARF-M10 groups, melatonin--5 mg/kg and 10 mg/kg, respectively--was administrated intraperitoneally. Forty-eight hours after the
glycerol injection, kidneys of the rats were taken under
anesthesia.
Arginase activity,
ornithine, and NO levels in the kidney tissue were determined.
Melatonin had an increasing effect on kidney tissue
arginase activities and
ornithine levels while decreasing NO concentration. It is possible that besides the direct scavenging effect, the stimulatory effect of
melatonin on
arginase activity may result in an inhibition of NOS activity and, finally, a decrease in the kidney NO level.