Temporal variation in serum nitrite levels in rats and mice

Although considerable evidence implicates involvement of nitric oxide (NO) in circadian regulation, little is known about possible 24h variations in b asal NO metabolism. In this study, daily variations in serum nitrite levels were studied in locally bred mice and rats during the months of September and October. The serum was separated from blood samples obtained at six dif ferent times of the day and night (1h, 5h, 9h, 13h, 17h, and 21h after ligh ts off [HALO] from male albino mice and rats). As an index of in vivo NO ge neration, serum nitrite levels (determined by the diazotization method) in rats exhibited significant temporal fluctuation (unpaired Student t test), with the concentration highest at 5 HALO and 21 HALO and lowest at 9 HALO. No such temporal variation was detected in mice in these studies conducted on locally bred animals in the autumn.