Effect of chronic uremia on fructose 2,6-bisphosphate glycolytic and gluconeogenic enzymes in rat liver

Intestinal Absorption and Hepatic Extraction of Propranolol and Metoprolol in Rats with Bilateral Ureteral Ligation

To investigate the mechanism responsible for the increased bioavailability of propranolol in bilateral ureter-ligated (BUL) rats, the intestinal absorption and hepatic extraction of propranolol and metoprolol were evaluated. The initial absorption rate of these drugs after intra-intestinal administration was only slightly increased in the BUL rats, whereas the blood drug concentration in these rats was higher than that in control rats. The blood propranolol and metoprolol concentrations during intra-portal infusion in the BUL rat were significantly higher than that in the control rat. In the presence of NADPH, the intrinsic metabolic activity of metoprolol in hepatic microsomes was not altered by BUL. On the other hand, the NADPH generation rate in the hepatic cytosol in the BUL group was lower than that in the control group. These results indicate that the absorption rate-dependent decrease in hepatic first-pass clearance of propranolol and metoprolol due to saturation kinetics is marginal, and that the hepatic metabolic activity and extraction of the drugs is significantly decreased in BUL rats probably due to the reduced NADPH generation rate in the liver.

Regulation of the fructose 6-phosphate/fructose 2,6-bisphosphate cycle by enzyme phosphorylation and sn-glycerol 3-phosphate

The regulation of the Fru-6-P/Fru-2,6-P2 cycle by the cooperation of allosteric and covalent mechanisms was investigated in a reconstituted enzyme system under in vitro conditions. Phosphorylation of the bifunctional enzyme exerts a much stronger effect than sn-glycerol 3-phosphate in lowering the quasi-stationary concentration of fructose 2,6-bisphosphate and in increasing the critical concentration of the fructose phosphates, respectively. However, sn-glycerol 3-phosphate is able to strongly amplify the decrease of the quasi-stationary concentration of fructose 2,6-bisphosphate due to phosphorylation. The experiments can be described by a mathematical model involving rate equations for the dephosphorylated and the phosphorylated PFD-2 and FBPase-2. The results are compared with data from the literature obtained under in vivo conditions.

Insulin resistance of uremia

Glucose intolerance is a nearly universal finding in patients with chronic renal failure and in animal models of uremia. The glucose intolerance results from impaired insulin-mediated glucose disposal by muscle, adipose, and liver tissue. Insulin binding by these tissues is not reduced. Rather, several defects exist in the postreceptor cascade of insulin action. Although impaired insulin-mediated glucose uptake and metabolism occur, the primary defect and causative agent are not established. The purpose of the present article is to review recent literature on the potential mechanisms underlying the insulin resistance of chronic renal failure.