The Movement of Solutes Across the Epithelium of the Ducts and Cisterns in the Mammary Gland of the Ewe

Abstract

The role of the cisterns and large ducts in the overall process of milk secretion has been studied in experiments which have been carried out to determine the change in composition of solutions injected into the mammary gland cisterns of lactating and dry ewes. These solutions contained electrolytes, lactose, and a marker substance and were allowed to remain in the gland for periods of up to 4 hr. The concentration of sodium, potassium, chloride, and lactose in the solution injected into lactating glands approached with time that in milk. The data indicated that the rate of change in concentration of sodium, potassium, and chloride was more rapid than could be accounted for by the mixing of the injected solution with milk from the ducts. Sodium, potassium, and chloride ions were secreted into solutions in which the concentrations of these ions were lower than those in milk and sodium and chloride ions were absorbed from solutions in which their concentration was higher than that in milk. Water absorption occurred from the solutions containing sodium and chloride ata higher concentration than that in milk. In the dry gland the composition of the solutions injected approached with time that of involution secretion which has a higher sodium and chloride and lower potassium and lactose concentration than normal milk. Lactose was absorbed from dry glands but not from the lactating glands.