The transfer of N-acetyl-4-aminoantipyrine and of thiocyanate from blood to milk

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Abstract
Summary: The entry into milk from blood of N-acetyl-4-aminoantipyrine (NAAP) and urea, compounds known to be distributed evenly throughout the whole of body water, and thiocyanate and thiosulphate, the distribution of which is confined largely to extracellular fluid, has been investigated. The concentrations of NAAP and urea in blood and in milk were similar, but the concentrations of thiocyanate and thiosulphate in milk were much lower than the concentrations in blood plasma. A progressive increase in the ratio of the thiocyanate concentration in milk to that in blood occurred with advancing lactation and marked variations in the thiocyanate ratio of the milk of the separate quarters were observed in some cows, and these variations in the ratio were closely related to variations in the chloride content of the milk; similar inter-quarter variations in the ratio for NAAP were not observed. With NAAP, there was a continuous equilibrium between blood plasma and milk within the udder, whereas with thiocyanate the content in milk after its secretion into the ducts and cisterns of the udder appeared to be largely independent of later changes in the concentration of thiocyanate in blood plasma. These results are discussed in relation to the secretion of chloride in milk.