Effect of prostaglandin E1 on hepatic cyclic AMP activity, carbohydrate and lipid metabolism

Glycogenolytic and haemodynamic responses to heat-aggregated immunoglobulin G and prostaglandin E2 in the perfused rat liver

Infusion of heat-aggregated immunoglobulin G (HAG) into perfused livers from fed rats caused transient increases in hepatic glycogenolysis and portal-vein pressure, accompanied by a transient increase in hepatic glycogen phosphorylase alpha content. The hepatic responses to HAG were inhibited by indomethacin (2 microM). In contrast, HAG was without effect on phosphorylase alpha content and glucose output in isolated hepatocytes. HAG infusion caused a transient decrease in hepatic cyclic AMP. Lowering the extracellular Ca2+ concentration to 6 or 50 microM attenuated markedly the glycogenolytic and haemodynamic responses to HAG; efflux of Ca2+ from the liver was not observed in response to HAG. Co-infusion of the specific platelet-activating-factor antagonist U-66985 (1-O-octadecyl-2-O-acetyl-sn-glycero-3-phosphoric acid 6'-trimethylammoniumhexyl ester) did not attenuate the glycogenolytic response to HAG. Infusion of prostaglandin E2 caused increases in glucose output, portal-vein pressure and the reduction state of the cytosolic NAD(H) redox couple similar to those seen with HAG. The present study suggests that the glycogenolytic activation after HAG infusion may be an indirect consequence of the haemodynamic response of the hepatic vasculature to stimulation of the reticuloendothelial cells of the liver.

Inhibition of glucagon-stimulated hepatic glycogenolysis by E-series prostaglandins

The effect of E-series prostaglandins (PGE) on hepatic glucose metabolism is controversial. This study uses isolated rat hepatocytes and exogenously added PGE analogs or frequent native PGE additions (to compensate for hepatic PGE degradation) to define PGE's effect on hepatic glycogenolysis. 16,16-Dimethyl PGE2, 15(S),15-methyl PGE2, PGE1 and PGE2 all inhibit glucagon-stimulated glycogenolysis. It is concluded that E-series prostaglandins can act directly on the liver to inhibit glycogenolysis.

Inhibitory effect of prostaglandins on the stimulation by glucagon and adrenaline of formation of cyclic AMP in rat hepatocytes

Several prostaglandins were found to inhibit hormone-induced cyclic AMP accumulation in suspensions of intact rat hepatocytes. Prostaglandin E1 in concentrations of 0.05--25 micrometers inhibited the cyclic AMP response to glucagon. Maximal inhibition was about 50%. The effect was rapid, being evident within 30 s. Prostaglandins E2, F1 alpha, F2 alpha, A1 and A2 also inhibited the glucagon effect on cyclic AMP in hepatocytes. In cells made highly responsive to adrenaline, by pretreatment of the animals with the carcinogen 2-acetylaminofluorene, and inhibitory effect of prostaglandin E1 was seen also on adrenaline-induced cyclic AMP accumulation. The mechanism of the inhibitory effect of prostaglandins on hormone-stimulated cyclic AMP accumulation was not clarified. Prostaglandin E1 did not inhibit glucagon binding to intact hepatocytes, and so far we have not been able to demonstrate any effect of the prostaglandins on the adenylate cyclase or phosphodiesterase in broken cell preparations. It is concluded that while several previous studies have shown that stimulatory effects of prostaglandins on cyclic AMP are only marginal or lacking in parenchymal liver cells the present data indicate that several prostaglandins exert strong inhibitory interference with hormone-induced cyclic AMP accumulation.

Secretin-like choleretic effect of prostaglandins E1 and E2 in cats

1. The effects of intraportal and hepatic arterial infusion of prostaglandins E1 and E2 on liver function and circulation was studied in fasting chloralose anaesthetized cats. 2. Infusion of the prostaglandins at rates of 0-1, 1-0 and 5-0 mug/kg.min caused a 35-40% increase in bile flow. This may be explained by a decrease in the reabsorption or a secretion of sodium ions by the ductular cells. The canalicular bile production and bile flow. This may be explained by a decrease in the reabsorption or a secretion of sodium ions by the ductular cells. The canalicular bile production and bile acid excretion was not affected by the prostaglandins. 3. Infused at rates of 1-0 and 5-0 mug/kg.min the prostaglandins caused a transient decrease in mean arterial blood pressure and mesenteric vascular resistance. The resistance in the intrahepatic arterioles and low-pressure vessels was not affected. 4. The prostaglandins did not influence the splanchnic uptake of oxygen and ethanol, whereas a slight increase in the splanchnic glucose output occurred. 5. The effects of the two prostaglandins were identical and not related to the route of administration.

Effect of PGE1 on gluconeogenesis and glycerol esterification in perfused liver of fasted rats

Using perfused livers of rats fasted for 48 hours, glucose production and incoroporation of 2-14C pyruvate (trace dose) into perfusate glucose were studied. Both were found to be inhibited by PGE1 (infuced at a concentration of 0.5 mu/min) by about 60%. The incorporation of 1-14C glycerol into perfusate glucose and into glycerol-glyceride part of the liver glycerides were also studied, using the same test conditions. The former incorporation was significantly inhibited (56%) and the latter strongly stimulated (360 %) by PGE1. PGE1 had no effect on glucose production in a perfusate overloaded with sodium pyruvate, nor on pyruvate carboxylase and phospho-enolpyruvate carboxykinase activity. this was in contrast with the results obtained in perfusions with a trace dose of 2-14C pyruvate. The results showed that PGE1, at the physiological concentration used, stimulated the incorporation of 1-14C glycerol into glycerol-glyceride part of liver glycerides and, when there was no overload of pyruvate present in the perfusion medium, inhibited gluconeogensis at some point, possibly, but perhaps not exclusively, between the glycerol and glucose steps.