Comparison of total body urea production potential with total body carbamoyl phosphate synthetase (CPS-1) activity in newborn piglets infused with alanine at 50% of resting energy expenditure for 36 hours.
The calculated rate of urea production [U(p); mmol urea/(h. kg(0. 75))], based on urinary urea-N (UUN) excretion and changes in total body urea-N, was compared with the calculated total body V(max) of carbamoyl phosphate synthetase (CPS-1) of 24 neonatal piglets from four treatments as follows: 6 h baseline control (n = 8), 18 h of alanine intravenously (IV) at 50% of resting energy expenditure (REE; n = 4), 36 h of alanine IV at 50% of REE (n = 6), or 36 h of glucose IV at 50% of REE (n = 6). The following significant increases from baseline were seen in piglets infused with alanine for 36 h: 1) UUN excretion [10.6 +/- 5.9 mg N/(h. kg(0.75)) to 53.2 +/- 11.1]; 2) BUN concentrations (9.1 +/- 3.0 mmol urea N/L to 51.2 +/- 7.0); 3) calculated urea production [0.34 +/- 0.21 mmol urea/(h. kg(0.75)) to 2.39 +/- 0.53]; and 4) CPS-1 V(max) [2.0 +/- 0.81 mmol citrulline/(h. kg (0.75)) to 4.4 +/- 1.5], (P < 0.05). With the exception of CPS-1 activity, significant decreases from baseline were seen in these values in piglets infused with glucose for 36 h (P < 0.05). Comparison of calculated urea production with calculated total body CPS-1 V(max) at baseline, 18 or 36 h after the start of infusion of alanine or glucose revealed a positive relationship (slope = 0.263; P < 0.002). At all enzyme activities, infusion of alanine resulted in a significant increase in the rate of urea production compared with controls (P < 0.001). Total body CPS-1 activity varied from 1.8 to 5.8 times that of urea production, suggesting that CPS-1 did not limit urea production.
Department of Nutritional Sciences, University of Wisconsin-Madison, 53706, USA.
J A
JA
Davis
F R
FR
Greer
N J
NJ
Benevenga
D000409:Alanine / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D001806:Blood Urea Nitrogen; D002222:Carbamoyl-Phosphate Synthase (Ammonia) / Q000378:metabolism*; D002956:Citrulline / Q000378:metabolism; D004734:Energy Metabolism; D007700:Kinetics; D013552:Swine / Q000378:metabolism*; D013997:Time Factors; D014508:Urea / Q000378:metabolism*
D002956:Citrulline; D014508:Urea; D002222:Carbamoyl-Phosphate Synthase (Ammonia); D000409:Alanine