AJP - Endocrinology and Metabolism, Vol 252, Issue 3 E408-E413, Copyright © 1987 by American Physiological Society
Alanine uptake by liver at midpregnancy in rats
M. Pastor-Anglada, X. Remesar and G. Bourdel
The participation of the liver to the increase in alanine utilization seen
at midpregnancy was studied in 9- and 12-day pregnant rats. Liver
fractional extraction of alanine was assessed in vivo from the changes in
concentration in afferent and efferent vessels. Hepatic active transport of
alanine was determined in vitro using isolated plasma-membrane vesicles.
Compared with nonpregnant controls, alanine fractional extraction was
significantly increased on day 12 but not on day 9 of pregnancy. Vesicles
isolated from 9- and 12-day pregnant animals had a greater capacity for
Na+-dependent transport than those from controls. Eadie-Hofstee plotting
showed that this increase was due to an increase in Vmax with no change in
Km. Both A and ASC systems contributed to the Vmax increase. These results
indicate that, although by day 9 the liver has developed an increased
capacity for alanine uptake, the actual extraction is seen only by day 12
of pregnancy. At this stage the liver participates actively in the turnover
of alanine and the development of hypoalaninemia.
