Improved Enzymatic Method for Determining Mannitol and its Application to Dog Serum after Mannitol Infusion

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Abstract
An enzymatic method for mannitol quantitation was developed. Its application in determining mannitol levels in serum samples from dogs after mannitol infusion is illustrated. The method is based on the spectrophotometric measurement of the initial rate of NADH formation in the reaction between mannitol and NAD catalyzed by mannitol dehydrogenase. A linear relationship between initial rates and mannitol concentration is seen between 17 .mu.mol/l and 6.7 mmol/l mannitol. From the extent of dilution of the serum sample in the assay this corresponds to serum levels of 0.5-200 mmol/l. Because of the high degree of substrate specificity of mannitol dehydrogenase and the extensive dilution of the serum sample in the assay reaction mixture, serum proteins and glucose do not interfere with the reaction. As a result, pretreatment of samples to remove glucose and deproteinization are unnecessary.