Nicotinamide coenzyme concentrations in mammary biopsy samples from ketotic cows

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Abstract
A fluorimetric method for assay of nicotinamide-adenine nucleotide coenzymes has been developed for mammary tissue. Modifications of a method previously described for rat liver were devised to minimize both loss of activity and the development of a yellow colour. The results obtained were then linear, recovery of added coenzymes was between 88 and 105%, and precision ranged from 4% of the mean for NAD to 13% for NADPH2. Six cows diagnosed as having spontaneous uncomplicated acetonaemia were purchased. Mammary biopsies were performed, yielding 5-10 g. of tissue, which was then assayed for the coenzymes. On the next day the cow was treated with glucose, dexamethazone or nicotinic acid, except for a doubtful case, which was not treated. When recovery of the cow appeared complete, one or two more biopsies and assays were performed to serve as controls. Comparison of typical cases with apparently fully recovered cows showed that the concentrations of all forms of the nicotinamide-adenine nucleotide coenzymes was lower than normal during acetonaemia, although the ratio of oxidized to reduced forms was not changed. These results were interpreted to mean that a shortage of all forms of these coenzymes, rather than failure to convert oxidized into reduced forms or vice versa, is a metabolic difficulty in this disease. Such a shortage could provide a common factor for the impaired oxidative and reductive reactions which occur in bovine acetonaemia.