INFLUENCE OF STAGE OF LACTATION ON GLUCOSE AND GLUTAMINE-METABOLISM IN ISOLATED ENTEROCYTES FROM DAIRY-CATTLE

Pathways of glutamine and glucose metabolism in early, mid-, and late lactation dairy cows were evaluated by in vitro incubations of enteroc ytes for 2 hours with [U-(14)-C]glutamine and [U-C-14]glucose. Enteroc ytes from early-lactation cows produced greater amounts of COP from gl utamine in concentrations that ranged from 2 to 8 mmol/L than enterocy tes from either mid- or late lactation cows. Enterocytes from early-la ctation cows also produced greater amounts of CO2 from 4 and 6 mmol/L glucose than enterocytes from either mid- or late-lactation cows. Glut amine was metabolized via glutaminolysis mainly to ammonia, alanine, a spartate, glutamate, and CO2, and more of these products were produced in enterocytes from early-lactation cows than from pooled mid- and la te-lactation (PML) cows. Glucose was metabolized mainly to lactate, as compared with pyruvate and CO2. Lactate and COP production were both greater in enterocytes from early-lactation cows than from PML cows. G lutamine as the sole substrate accounted for all the energy requiremen ts of enterocytes from early-lactation cows but contributed only 31% i n the presence of glucose. Similarly, glucose accounted for all the en ergy requirements of enterocytes from early-lactation cows and contrib uted 69% in the presence of glutamine. In enterocytes from all cows, t he rate of adenosine triphosphate (ATP) production was greater in the presence of both glucose and glutamine compared with that in the prese nce of either substrate alone. The rate of production of ATP from gluc ose as the sole substrate was two to three times greater than that obt ained from glutamine as the sole substrate in enterocytes from all gro ups of cows. Thus, we suggest that although glutamine is an important energy source for enterocytes, it is not quantitatively as important a s glucose as an energy source for enterocytes from lactating cows. Cop yright (C) 1995 by W.B. Saunders Company