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THE RELATIONSHIP BETWEEN UREA AND PYRIMIDINE DE NOVO SYNTHESIS IN RUMINANT LIVER
Author(s) -
Motyl Tomasz,
Orzechowski Arkadiusz,
Pierzynowski Stefan
Publication year - 1988
Publication title -
quarterly journal of experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0144-8757
DOI - 10.1113/expphysiol.1988.sp003106
Subject(s) - orotic acid , urea cycle , urea , chemistry , ornithine transcarbamylase , ammonia , norvaline , carbamyl phosphate , pyrimidine metabolism , glycine , pyrimidine , medicine , biochemistry , valine , amino acid , purine , arginine , enzyme
The influence of ammonia and inhibition of the urea cycle by norvaline on orotic acid synthesis in five Polish Merino ewes was investigated. The sheep were exposed to 60 min of successive infusions of 0·9% NaCl, NH 4 Cl (20 µmol kg ‐1 min ‐1 ), and NH 4 Cl with DL‐norvaline (10 µmol kg ‐1 min ‐1 ) solutions administered to the mesenteric vein. The average rate of orotic acid output, urea output and ammonia uptake in the liver in control conditions (infusion of 0·9% NaCl) was: 1·09 nmol g ‐1 min ‐1 0·97 µmol g ‐1 min ‐1 and 0·94 µmol g ‐1 min ‐1 , respectively. Ammonia significantly stimulated the orotic acid output, urea output and ammonia uptake. At the same time liver uptake of glutamic acid, alanine and glycine increased. Norvaline as a competitive inhibitor of ornithine transcarbamylase depressed citrulline release and urea output in the liver, and elevated, although not significantly, the orotic acid output. It was concluded that ammonia stimulates the de novo synthesis of pyrimidine in the sheep liver but the participation in this effect of carbamyl phosphate generated in the urea cycle is limited.