AbstractRates of secretion of milk constituents (fat, protein, lactose, Na+and K+) in the lactating goat were measured under normal circumstances and after injections of ouabain. In all experiments a close association was noted in the secretion rates for protein, lactose and K+. Under the influence of ouabain, the concentration of Na+in the milk tended to rise and that of K+to fall. The rate of milk fat secretion varied independently from the rates for the other constituents. It is reasonably assumed that the principal mechanism of milk protein secretion is by emptying of Golgi vesicles through the plasma membrane. The close correlation in rates for protein, lactose and K+supports the contention that all three are assembled in Golgi vesicles and secreted by the same mechanism.
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