AJP - Gastrointestinal and Liver Physiology, Vol 254, Issue 4 602-G609, Copyright © 1988 by American Physiological Society
Kinetics of hepatic alanine uptake and urea synthesis in pigs
H. Vilstrup and L. T. Skovgaard
Division of Hepatology and Experimental Pathology, Rigshospitalet, Copenhagen, Denmark.
The kinetics of hepatic alanine uptake and urea synthesis in relation to
sinusoid alanine concentration was investigated in seven anesthetized pigs
weighing 63 kg, using liver vein catheterizations. Each experiment consists
of four steady-state periods of 40 min with alanine concentrations in the
range of 0.4-27 mmol/l. The process rates were measured as the products of
transhepatic concentration gradients and hepatic blood flow rate,
determined by indocyanine green. The data suggest that both processes
follow saturation kinetics, that there exists a sinusoidal concentration of
alanine below which net removal is limited, and that urea synthesis
consists of two components: one alanine independent and one depending on
alanine concentration according to Michaelis-Menten kinetics. The kinetic
parameters were estimated iteratively by the maximum likelihood method. The
maximum rate of alanine uptake was 1.13 +/- 0.74 mmol.min-1.kg liver wt-1
(mean +/- SD), the alanine concentration resulting in half-maximum alanine
uptake rate was 1.69 +/- 0.99 mmol/l, and the removal-limiting alanine
concentration was 0.27 +/- 0.09 mmol/l. The maximum rate of urea-N
synthesis was 1.49 +/- 0.87 mmol.min-1.kg liver wt-1, the alanine
concentration resulting in half-maximum urea-N synthesis rate was 2.32 +/-
1.11 mmol/l, and the alanine concentration-independent urea-N synthesis
rate was 0.13 +/- 0.10 mmol.min-1.kg liver wt-1.
