Studies of Mammary Amino Acid Transport

Abstract

Experiments were conducted to study several different aspects of mammary amino acid transport. The experimental animals utilized were cow and rat. The major conclusions include the following: (1) Mammary tissue was shown to have relatively high (gamma)-glutamyl transpeptidase activity, and activity increased at the onset of lactation. This increase was shown to be dependent on prolactin. The timing and magnitude of the changes in (gamma)-glutamyl transpeptidase activity during pregnancy, lactation, and involution, as well as the involvement of prolactin in the adaptations which occur during lactogenesis, suggest this enzyme plays an important role in mammary function. These results would be consistent with a role for this enzyme in amino acid transport. (2) The plasma concentration of glutathione in bovine blood was found to be very small and no significant arterio-venous difference of plasma glutathione was detected across the mammary gland. However, a significant difference in whole blood glutathione was observed. It is possible that glutathione might be acted on by mammary (gamma)-glutamyl transpeptidase, thus supplying amino acids for milk-protein synthesis. (3) Bovine mammary slices were used to measure in vitro uptake of amino acids. The amino acid uptake pattern by slices was similar to uptake by the cow udder in vivo. This suggests that slices can be used as a valid system in the study of mammary amino acid transport.