title: Glucagon increases hepatic efficacy for urea synthesis.
abstract: The effect of glucagon on the relation between urea synthesis and blood amino acid concentration was studied in seven healthy volunteers. Alanine was given as prime-continuous infusions and, after 1 hr for equilibration, the urea nitrogen synthesis rate was measured in two periods of about 2 hrs as urinary excretion corrected for accumulation and intestinal hydrolysis. During one of the periods, glucagon was infused to obtain a constant concentration of 200-1200 ng/l. The spontaneous urea synthesis during the alanine infusion was 86-141 mmol/hr and linearly related to the alanine concentrations of 1.33-2.99 mmol/l. The hepatic clearance of alanine-nitrogen to urea-nitrogen, assessed by the ratio between the increase in the urea synthesis rate and alanine concentration, was 23 +/- 4 l/hr (mean +/- S.D.). Glucagon increased the rate of urea synthesis by 35 +/- 11 mmol/hr (p less than 0.02) and decreased the alanine concentration by 0.22 +/- 0.06 mmol/l (p less than 0.01). Glucagon increased the hepatic nitrogen clearance to an average of 42 +/- 13 l/hr (p less than 0.01). The difference between infusion of amino-nitrogen and appearance of urea-nitrogen was +15 +/- 10 mmol/hr during alanine infusion alone and -11 +/- 25 mmol/hr during exogenous glucagon. The loss of nitrogen could be accounted for by depletion of non-alanine amino acids from the blood. Glucagon increases the efficacy of urea synthesis, which may be of importance for catabolism by changing the hepatic contribution to nitrogen homeostasis.
authors.affiliation: Division of Hepatology, Rigshospitalet, Copenhagen, Denmark.
authors.forename: H
authors.initials: H
authors.lastname: Vilstrup
authors.forename: B A
authors.initials: BA
authors.lastname: Hansen
authors.forename: T P
authors.initials: TP
authors.lastname: Almdal
mesh_terms: D000328:Adult; D000409:Alanine / Q000494:pharmacology; D005260:Female; D005934:Glucagon / Q000494:pharmacology*; D006801:Humans; D007260:Infusion Pumps; D008099:Liver / Q000378:metabolism*; D008297:Male; D009584:Nitrogen / Q000378:metabolism; D012016:Reference Values; D014508:Urea / Q000378:metabolism*
chemical_list: D014508:Urea; D005934:Glucagon; D009584:Nitrogen; D000409:Alanine