0000000000953891
AUTHOR
Javier Marti
Regulation of the Urea Cycle during Lactation
We have recently shown that the uptake of amino acids by rat lactating mammary gland is 15 mmoles/day (1). This effect is achieved by an increase in food intake during lactation and probably by changes in amino acid metabolism in other tissues. Rat liver removes 75% of the total amino acids derived from a protein meal (2); therefore plays a key role in the regulation of plasma amino acid concentration.
Effect of Thyroid Hormones on Urea Biosynthesis and Related Processes in Rat Liver*
The results of the few studies on the effect of the thyroid status on nitrogen metabolism have been inconclusive and/or contradictory. In an attempt to elucidate this important relationship, we have studied the effect of experimental hypo- and hyperthyroidism on urea biosynthesis and related processes. We have found that the capacity of the liver to synthesize urea was increased in hypothyroid rats, as were the activities of the urea cycle enzymes; there were also changes in the activities of some related enzymes and in the levels of intermediates and amino acids. Isolated hepatocytes from these rats showed an increased capacity for urea synthesis. In hyperthyroid rats the picture was more …