title: Cerebral metabolism of amino acids and glucose in fed and fasted sheep.
abstract: Net cerebral uptake from or release into whole blood of oxygen, carbon dioxide, glucose, amino acids, lactate, pyruvate, ketone bodies, and acetate was estimated in fed, 3-day-fasted, and 6-day-fasted sheep. The respiratory quotient was similar in all three groups of sheep (approximately 0.95). Glucose uptake (35 mumol X min-1 X 100 g-1) was maintained during fasting, and about 94% of the cerebral oxygen consumption could have been accounted for by glucose oxidation in all sheep. A cerebral uptake of the branched-chain amino acids (leucine, isoleucine, and valine) and proline also was observed with a concomitant production of glutamine and asparagine. The brains of fed and 3-day-fasted sheep were in nitrogen balance, but a small net release of nitrogen occurred in 6-day-fasted sheep (2 mumol N. min-1 X 100 g-1). A small amount of pyruvate was always released (1.4 mumol X min-1 X 100 g-1) into the blood, whereas lactate was released (6 mumol X min-1 X 100 g-1) only in 6-day-fasted sheep. Ketone body and acetate utilization always was negligible when compared with that for glucose. The total cerebral nonglucose carbon release found for 6-day-fasted sheep was equivalent to 23% of the glucose carbon taken up, although only 8% could have been derived directly from glucose. Thus, metabolism by the ovine brain seems resistant to prolonged periods of hypoglycemia with only small adaptations occurring after a 6-day fast.
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002560:Cerebrovascular Circulation; D005215:Fasting; D005260:Female; D005947:Glucose / Q000378:metabolism*; D007657:Ketone Bodies / Q000378:metabolism; D007700:Kinetics; D007773:Lactates / Q000378:metabolism; D019344:Lactic Acid; D008297:Male; D010101:Oxygen Consumption; D011773:Pyruvates / Q000378:metabolism; D019289:Pyruvic Acid; D012756:Sheep
chemical_list: D000596:Amino Acids; D007657:Ketone Bodies; D007773:Lactates; D011773:Pyruvates; D019344:Lactic Acid; D019289:Pyruvic Acid; D005947:Glucose