In vivo studies on methemoglobin formation by sodium nitrite

The oral LD5o of NaNO₂ for rats was found to be 0.15 g per kg body weight. The methemoglobin level increased to 45-80%, 1 h after the administration of the LD5o dose and returned to the normal level after 24 h. The dose-maximum methemoglobin concentration curve was found to be Sshaped. Formation of nitrosyl hemoglobin preceded that of methemoglobin, its maximum concentration being a quarter of that of the latter derivative. In rats receiving 0.5% NaNO₂ as drinking water, the concentration of methemoglobin showed a characteristic daily change (4 to 88%) due to the circadian rhythm of the animal in drinking. After 6 months, slight nitrosyl hemoglobin production, Heinz body formation, anisocytosis, and hypohemoglobinemia were observed.