[Adaptive shifts in the activity of amino acid transport into mammary secretory cells in changed nutritional conditions].
On the basis of analysis of published data, direct (using 13C) and indirect methods of estimating the amino acid transfer into mammary secretory cells in vivo were compared and the modified indirect method was used to determine quantitatively the shifts in transport activity in lactating cows and goats in trials with amino acid deficit or excess and in investigations that used a hyperinsulemic-euglycemic clamp. The analysis suggests that inadequacy of traditional use of extraction efficiency as a measure of tissue affinity to substrate is associated with two shortcomings: 1) if the changes in mammary blood flow are more expressed compared to transport activity, the arteriovenous difference and extraction efficiency may change in opposite direction to the shifts in transport activity; 2) due to the effect of nonlinearity, in situations characterized by small ratio of blood flow: the transport activity extraction efficiency is insensitive to shifts on activity of transport. The re-analysis of published data using the modified inbdirect method indicated that the deficit of individual amino acid caused a rise in activity of their transport and the excess decreased a net transfer into cell. The insulineuglycemic clamp treatments increased the activity of amino acid transport into the mammary cell and milk protein yield. The results obtained suggest that net transmembrane transfer of amino acid into mammary secretory cell can be controlled by the cell itself according to metabolic demand.
Cherepanov
G G
GG
Makar
Z N
ZN
D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D006041:Goats; D007774:Lactation / Q000502:physiology*; D008297:Male; D008321:Mammary Glands, Animal / Q000378:metabolism*
D000596:Amino Acids