INSULIN AND GLUCAGON REGULATION OF GLUCONEOGENESIS IN PRERUMINATING AND RUMINATING BOVINE

Hepatocyte monolayers were established from young preruminating (7 to 14 d of age) or older ruminating (11 to 12 wk of age) calves and used to evaluate the effects of insulin and glucagon on incorporation of ca rbon from 2.5 mM [2(-14)C]propionate and 2.0 mM [U-14C]lactate into gl ucose and glycogen. Developmental state (young preruminating vs older ruminating) of the donor calf did not affect the rate of gluconeogenes is from propionate in the absence of hormones. Insulin decreased (P < .05) gluconeogenesis and increased (P < .05) glycogenesis from propion ate and lactate in hepatocytes from preruminating calves but had no ef fect on hepatocytes from ruminating calves. Lactate was poorly metabol ized to glucose and was not responsive to glucagon in hepatocytes from ruminating calves compared with hepatocytes from preruminating calves . Hepatocytes responded to glucagon by increasing (P < .05) gluconeoge nesis from propionate. Maximal responsiveness to glucagon did not diff er between ruminating and preruminating calves, but hepatocytes from p reruminating calves responded at lower glucagon concentrations (P < .0 5). These data demonstrate a similar capacity of hepatocytes from prer uminating and ruminating calves to metabolize propionate to glucose, b ut there was a seven- to eightfold decrease in gluconeogenesis from la ctate in ruminating calves that was accompanied by a decreased respons e to acute changes in insulin and glucagon.