The metabolic cost of hepatic ammonia detoxification
K.B. Greaney, G.W. Reynolds, M.J. Ulyatt, D.D.S. Mackenzie and
P.M. Harris
AgResearch, Private Bag 11008, Palmerston North, New Zealand.
Proceedings of the New Zealand Society of Animal Production, 1996,
56: 130-132
The quantity of ammonia removed from portal blood by the ovine
liver was measured using four sheep prepared with in-dwelling catheters in
the hepatic region and fed either lucerne pellets (L) or white clover (WC) at
900 gDM/day. Following blood sampling, plasma ammonia and oxygen
concentrations were determined. The portal ammonia concentration and
flow were significantly (P<0.01) affected by the diet (304 and 646 µM; 641
and 1480 µM/min respectively). The ammonia flow across the liver was
significantly (P<0.01) affected by the diet (-578 and -1346 (µM/min
respectively). Hepatic oxygen consumption for the L diet was significantly
(P<0.05) less than that for WC (1.6 and 2.8 mM/min respectively), of which
24 and 32% respectively can be directly attributed to ammonia detoxication
to urea.
This work confirms earlier reports (Lobley et al., 1995) that the ovine liver
can detoxify at least 1400 µM/min of ammonia from the portal blood, albeit
at an elevated metabolic cost.
Keywords: NZSAPAB;
Ammonia; protein digestion; liver; sheep.
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Last Updated 18-03-1997
