Rate of Formation and Reduction of Nitrite-Induced Methemoglobin In Vitro and In Vivo as Influenced by Diet of Sheep and Age of Swine

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Abstract
Drenching sheep twice daily with a sucrose solution providing 60 gm. of sugar per day, or the addition of 500 gm. of corn per day to a forage ration, offered a large degree of protection against the methemoglobinemia induced by 20 gm. of orally-administered sodium nitrate. Substitution of 100 gm. of soybean meal for an equal amount of corn appeared to reduce the protection provided by the corn. When 0.03 gm. of sodium nitrite per kg. of body weight was given by intravenous injection, no differences in methemoglobin values were observed for sheep on the various rations. No differences in the rate of methemoglobin formation or reduction were apparent when blood from these sheep was incubated in vitro with sodium nitrite. These data indicate that the effect of dietary variations on the severity of nitrate toxicity in sheep was probably due almost entirely to variations in nitrite accumulation in the digestive tract and not to differences in the rate of methemoglobin formation or reduction per se. Pigs given intravenous injections of 0.03 gm. sodium nitrite per kg. of body weight developed a lower degree of methemoglobinemia when treated at 1 week of age than the same pigs when similarly treated at approximately 3 months and 5½ months of age. While peak methemoglobin values (percent methemoglobin) obtained under in vitro conditions for the pigs of various ages were similar, a slower rate of methemoglobin reduction was observed for pigs at 5½ months of age. This difference in rate of methemoglobin reduction could not be explained on the basis of differences in reduced glutathione content of the blood, which tended to increase with increase in age, nor was it confirmed under in vivo conditions. These data indicate that heathy pigs 1 week of age were no more susceptible to nitrite-induced methemoglobinemia than the same pigs when older.