Effects of protein kinase C modulation on hepatic hemodynamics and glucoregulation

This study evaluated the effects of PKC activation using phorbol 12-myristate 13-acetate (PMA) and PKC inhibition using the isoquinoline sulfomide derivative H-7 on hemodynamics and glucoregulation in the isolated perfused rat liver. Livers were isolated from fed male Holtzman rats and perfused with Krebs Ringer bicarbonate solution under a constant flow of 50 ml/min at 35degreeC. Portal vein pressure, glucose and lactate concentrations in the medium and oxygen consumption rates were continuously monitored by a Grass polygraph, YSI glucose and lactate monitors, and a YSI oxygen monitor, respectively. PMA at concentration of 2 to 200 nM increased the portal vein pressure, glucose and lactate production, but decreased oxygen consumption rate in a dose-dependent fashion. H-7 (200 micrometer) attenuated PMA (50 nM)-induced vasoconstriction (15.1+/-1.36 vs 10.56+/-1.17 mmHg), glucose production rate (91.3+/-6.15 vs 71.8+/-2.50 micromoles/g/hr), lactate production rate (72.4+/-6.82 vs 53.6+/-4.82 micromoles/g/hr) and oxygen consumption rate (33.7+/-1.41 vs 27.9+/-1.75 microliter/g/min). The effects of PMA were blocked either by addition of verapamil (9 micrometer) or perfusion with Ca2+-free KRB. These results suggest that the hemodynamic and glucoregulatory changes in the perfused rat liver are mediated by protein kinase C activation and require Ca2+ influx from the extracellular fluid.

Enhancement of O-dealkylation in Mouse Liver by Dietary Administrations of BHA and BHT: Studies with Isolated Perfused Livers and Hepatic Microsomes

Effects of feeding 2(3)-tert-butyl 4-hydroxyanisole (BHA) and 3, 5-di-tert-butyl 4-hydroxytoluene (BHT) on the rates of mixed function oxidation and conjugation enzyme reactions have been determined using isolated hepatic microsomal fractions and isolated perfused livers of mice. The treatments with either of the antioxidants have increased the rates of O-demethylation for p-nitroanisole and of O-deethylation for 7-ethoxycoumarin up to 2-fold, both in microsomes and in perfused liver. Analysis of the perfusate showed that the increased amounts of p-nitrophenol and 7-hydroxycoumarin produced by the elevated mixed-function oxidase activities were reflected by the increase in the amounts of glucuronide conjugates and not in the increase for the amounts of the sulfate ester conjugates. Comparison of results also indicated that in the perfused liver, the maximal rate of metabolite conjugation is limited by the maximal rates of the initial mixed function oxidase activities.