INTERACTIONS BETWEEN RUMINAL DEGRADABLE NITROGEN INTAKE AND IN-VITRO ADDITION OF SUBSTRATES ON PATTERNS OF AMINO-ACID-METABOLISM IN ISOLATED OVINE HEPATOCYTES

The effects of ammonia (as NH4Cl) and propionate on the partitioning o f amino acids between oxidation and gluconeogenesis were determined in isolated hepatocytes obtained from sheep fed a basal diet (50:50 brom egrass hay:corn; as-fed basis) with or without urea. Hepatocyte suspen sions were incubated with NH4Cl (0, 1.25, 2.5 and 5.0 mmol/L) and/or p ropionate (0, 2.5 and 5.0 mmol/L), in the presence of either 2.5 mmol/ L L-alanine and 18.5 kBq L-[1-C-14]alanine or 2.5 mmol/L L-glutamate a nd 18.5 kBq L-[1-C-14]glutamate. Increasing the level of ruminal degra dable nitrogen with urea increased in vitro rates of oxidation to, (CO 2)-C-14 of [1-C-14]alanine, but not [1-C-14]glutamate. Increasing in v itro concentrations of NH4Cl and propionate between 0 and 5 mmol/L red uced the rates of oxidation to (CO2)-C-14 of both [1-C-14]alanine and [1-C-14]glutamate. Synthesis of [C-14]glucose with [C-14]alanine, but not [1-C-14]glutamate as the substrate, was increased 100% by feeding urea. Increasing in vitro levels of NH4Cl between 0 and 5 mmol/L reduc ed the rates of conversion of [1-C-14]alanine and [1-C-14]glutamate to [C-14]glucose in hepatocytes isolated from sheep fed both diets. incr easing in vitro levels of propionate between 0 and 2.5 mmol/L elevated production rates of [C-14]glucose from both radiotracers, but from 2. 5 to 5.0 mmol/L propionate no further increase was evident. Feeding ur ea increased in vitro rates of urea nitrogen production. Increasing pr opionate levels between 0 and 5 mmol/L reduced ureagenic rates in live r cells isolated from sheep fed both diets. Oxygen (O-2) uptake was un affected by diet and NH4Cl; however, increasing propionate between 0 a nd 5 mmol/L increased rates of O-2 uptake. It is concluded that in iso lated sheep hepatocytes, detoxification of excessive ammonia may cause a repartitioning of alanine and glutamate metabolism towards oxidatio n and gluconeogenesis.