Effect of fasting on amino acid metabolism by lactating mammary gland: studies in women and rats.
Concentrations of free amino acids were measured in human milk and arterial blood from lactating women after an overnight fast or after a controlled breakfast. The concentrations of many free amino acids in milk (except L-tyrosine, L-aspartate, L-asparagine, L-glutamate and L-glutamine) were lower after an overnight fast than after breakfast. Similarly, the arterial concentrations of amino acids were lower except for L-asparagine, L-alanine, L-tyrosine and L-phenylalanine. Net uptake of amino acids by the mammary gland of the lactating rat was significantly lower after starvation for 6 or 24 h than in the fed state because the arteriovenous differences of amino acids and the blood flow were significantly lowered. Starvation produced a significant decrease of 2-amino-[1-14C]isobutyric acid uptake by isolated acini from lactating rat. These results show that short-term starvation decreases the amino acid supply and transport in mammary gland as well as the free amino acid concentration in milk.
D000596:Amino Acids / Q000378:metabolism*; D000621:Aminoisobutyric Acids / Q000378:metabolism; D000818:Animals; D001940:Breast / Q000098:blood supply / Q000378:metabolism*; D005215:Fasting; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007774:Lactation; D008321:Mammary Glands, Animal / Q000098:blood supply / Q000378:metabolism*; D008895:Milk, Human / Q000378:metabolism; D011247:Pregnancy; D051381:Rats; D011919:Rats, Inbred Strains; D012039:Regional Blood Flow
D000596:Amino Acids; D000621:Aminoisobutyric Acids; C100049:2-aminoisobutyric acid