Perfusion of the isolated mammary gland of the goat.

Abstract

Improvements to a previously reported technique for the perfusion of isolated goat mammary glands are described. Secretion of milk of relatively normal composition in vitro has been maintained at approximately 50% of the in vivo rate for about 12 hr. Factors found to be important for successful perfusion are a normal rate of mammary blood flow, the provision of adequate glucose, acetate and amino acids, and the inclusion in the circuit of an efficient oxygenator and dialyser.Contrary to earlier results successful perfusions have been performed with glands from anaesthetized and from shot animals, although removal of glands from the tranquillized animal under spinal anaesthesia is still preferred. There was a marked dependence of milk secretion rate on the rate of blood flow below a critical value, but at supra‐normal flows there was no correlation between these variables. Evidence has been obtained suggesting that kinins or similar substances may be formed during perfusion.The specific dependence of milk secretion on glucose is again stressed. Other carbohydrates sustained oxygen consumption similar to that shown with glucose, but by contrast did not support the secretion of water, a small amount of milk low in lactose but high in fat and protein being produced. Although milk fat secretion was dependent on the provision of acetate, the omission of β‐hydroxybutyrate, lactate and neutral fat (all shown to be absorbed by the gland in vivo) from the substrate mixture did not seriously impair milk fat secretion in vitro. Amino acids were shown to be necessary for normal rates of milk protein secretion, but the alteration of the substrate mixture to correspond to the amino acid absorption observed in vivo produced no significant change in milk secretion from that observed when amino acids were infused at rates corresponding to their occurrence in casein. The infusion of B vitamins and various hormones had no effect on milk secretion. Perfusions carried out with a conscious goat in circuit were no more successful than the completely in vitro system, but glands grafted onto recipient goats (even males) following complete removal from the donors produced substantially more milk than in vitro preparations.In some experiments milk [Na] and [Cl] increased during perfusion while [K] and [lactose] decreased, these trends being apparent in milk secreted before perfusion was begun and being probably due to the oxytocin used to produce milk ejection. In other experiments milk [Na] and [Cl] showed little change but [K] and [lactose] tended to rise.Possible factors limiting the performance of perfused organs are discussed.