Amino Acid and Glucose Uptake by the Isolated Perfused Guinea‐pig Mammary Gland

Abstract

A technique has been developed for perfusion of the isolated guinea-pig mammary gland. Perfusate flow rates per unit weight of tissue were similar to in vivo mammary blood flow in lactating rats and 2-3 times mammary blood flow in the lactating cow and goat.Amino acid uptake was measured by the arterio-venous difference technique. The uptake of 'essential' amino acids correlated with their relative content in guinea-pig milk protein, but uptake of 'non-essential' amino acids was insufficient to account for the predicted rate of protein synthesis. Uptake of most amino acids was dependent on the rate of supply of exogenous substrates. Glucose uptake was variable but mean uptake during perfusion correlated with the rate of substrate infusion and gland weight. After addition of [U-14C]glucose to the perfusate in one experiment, alanine, serine, glutamic acid, aspartic acid and proline residues in milk casein became significantly labelled.The maintenance of high perfusate flow rates was found to depend on the attention paid to filtration of the perfusate, but the rate of amino acid uptake was probably dependent on the availability of tryptophan.

Modelling Mammary Metabolism in the Dairy Cow to Predict Milk Constituent Yield, with Emphasis on Amino Acid Metabolism and Milk Protein Production: Model Construction

“…Histidine, lysine, methionine, the combined pool of tyrosine plus phenylalanine, and threonine were chosen as state variables because of their potential to be rate limiting in relation to milk protein synthesis (Mepham, 1982;Fraser et al, 1991). Histidine, methionine and TP are members of the group I EAA as denoted by Davis & Mepham (1974, 1976 which show mammary gland uptakes that agree very closely with their outputs in milk protein. However, the possibility that tryptophan could be limiting milk protein synthesis warrants evaluation.…”

Physiology and Biochemistry of Lactation

“…Use of the isolated perfused guinea pig mammary gland preparation (S.R. Davis and Mepham, 1974) is thought to avoid such problems, and when used in conjunction with the 'paired tracer' technique of Yudilevich et al (1979) permits measurement of both entry and efflux of amino acids. Evidence has been presented, using this technique, for the presence in guinea pig mammary glands at peak lactation of A, L, ASC and y+ systems, but A system activity was assessed as very low (Mepham et al, 1984).…”

Effects of Exogenous Cortisol on the Uptake of Corticosteroids by the Isolated Perfused Guinea-Pig Mammary Gland

“…The following experiments were undertaken to elucidate the role of corticosteroids during lactation in the guinea-pig and to determine any effects of corticosteroids on the uptake of amino acids by the isolated perfused mammary gland. materials and methods Perfusion technique The method was that described by Davis «ft Mepham (1974) with the minor modifications given by Peters (1977). Guinea-pigs were of the Dunkin-Hartley strain from the Sutton Bonington colony and glands for perfusion were removed 7-10 days post partum.…”