Effects on other milk components

In addition to its effects on synthesis of milk proteins themselves, prolactin also induces the production in the mammary gland of other proteins/enzymes involved in production of milk components. Lactose synthetase and enzymes of lipid metabolism, including acetyl-CoA carboxylase and lipoprotein lipase, are among these inducible enzymes [75]. 

Prolactin also stimulates the sodium/potassium ATPase of the mammary gland, leading to uptake of potassium ions and extrusion of sodium ions from the epithelial cells [78]. Via this and other effects the hormone probably plays an important part in regulating salt and water relationships in the mammary gland. Milk secretion involves a considerable loss of both water and salts from the mother, and control of these is of crucial importance. 

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