Down-regulation in vivo of PGE receptors and adenylate cyclase stimulation

Effects of prostaglandins on ethanol damage in primary cultured rat hepatocytes

OBJECTIVES

Several reports demonstrated that ethanol administration impairs the DNA synthesis in rat hepatocytes. Also, it has been demonstrated that prostaglandin (PG) helps prevent membrane damage by hepatotoxic chemicals. In this study, the authors examined PG's effects on the toxicity of ethanol in the primary culture of rat regenerations.

METHODS

We examined two kinds of parameters, i.e., DNA synthesis and lipid peroxidation in the primary culture of rat hepatocytes. Hepatocytes were isolated by the collagenase perfusion method. The rate of DNA synthesis was determined by pulse-labelling cultured cells with [3H]-thymidine. Incorporation of (3H)-thymidine was determined by liquid scintillation spectrophotometer. DNA content was measured by the fluorescence spectrophotometer. The lipid peroxidation was assayed with spectrophotometer.

RESULTS

The results were as follows: 1) PG family (PGA1, PGD2, PGE1, PGE2, PGG2a, PGI2 & Thromboxane B2) stimulated the DNA synthesis of hepatocytes (especially PGD2 and PGE1), 2) ethanol decreased DNA synthesis by clear dose-dependent manner, 3) the combined treatment of PGD2 or PGE1, prevents the decreasing of DNA synthesis, which was induced by ethanol, 4) in ethanol treatment, lipid peroxidation was decreased significantly, but PGD2, PGE1 and PGA1 were not affected, and 5) PGD2, PGE1 and PGA1 decreased lipid peroxidation with ethanol, significantly.

CONCLUSIONS

From these results, we concluded that PG could be useful for the treatment of degenerative liver disease and alcohol-induced liver disease in the assumption that further studies on the action mechanisms of PG will continue.

Acetylsalicylic acid (ASA) protects the prostaglandin-cAMP-system of human hypernephroma cells against irradiation-induced alterations

There is abundant evidence that inhibitors of prostaglandin (PG) biosynthesis might increase the radioresponse of certain tumour cells. This study investigated specific PG binding sites, eicosanoid production as well as intracellular cAMP levels in cultured human hypernephroma cells derived from 11 patients upon nephrectomy. Scatchard analyses of the binding data revealed specific PGE1-, PGE2- as well as PGI2-binding sites (PGE1: Bmax = 755 +/- 206 fmol mg-1 protein, Kd = 3.7 +/- 2.7 nM PGE2: Bmax = 494 +/- 221 fmol mg-1 protein, Kd = 4.2 +/- 2.5 nM; PGI2: Bmax = 693 +/- 164 fmol mg-1 protein, Kd = 6.0 +/- 4.5 nM). Significant (P < 0.01) increase in PG binding sites expressed on human hypernephroma cells (PGE1: Bmax = 1084 +/- 303 fmol mg-1 protein, Kd = 2.8 +/- 1.3 nM; PGE2: Bmax = 663 +/- 309 fmol mg-1 protein, Kd = 2.2 +/- 1.5 nM; PGI2: Bmax = 1021 +/- 391 fmol/protein, Kd = 4.2 +/- 3.6 nM) and inhibition of PG biosynthesis (TXB2: -82.5%, PGE2: -87.5%. PGD2: -80.6%, PGF2: -81.3%) were found after acetylsalicylic acid (ASA)-treatment (0.5 mg 10(-6) cells for 24 h). Following irradiation (60Co, 1.0 Gy/min-1 over 10(min), PG binding sites (PGE1: Bmax = 266 +/- 153 fmol mg-1 protein, Kd = 5.0 +/- 5.0 nM; PGE2: Bmax = 148 +/- 66 fmol mg-1 protein, Kd = 4.7 +/- 3.6 nM; PGI2: Bmax = 325 +/- 194 fmol mg-1 protein, Kd = 6.8 +/- 7.1 nM) were significantly (P < 0.01) diminished. However, irradiation had no significant effect on PG binding sites in ASA-pretreated cells (PGE1: Bmax = 699 +/- 240 fmol mg-1 protein, Kd = 3.5 +/- 1.8 nM; iloprost: Bmax = 766 +/- 452 fmol mg-1 protein, Kd = 3.2 +/- 2.2 nM). Although there was no significant difference in the basal values for cAMP between control and ASA-treated group cells, the PG-induced cAMP-production was less pronounced in the control group. Taken together, the findings suggest that ASA may modify the radioresponse of cultured human hypernephroma cells by preventing the decrease of PG binding sites induced by irradiation.

Effect of nonsteroidal anti-inflammatory drugs on glycogenolysis in isolated hepatocytes

E-series prostaglandins have previously been demonstrated to inhibit hormone-stimulated glycogenolysis when added to isolated hepatocytes of the rat. In the present study, the effect of nonsteroidal anti-inflammatory drugs, which inhibit cyclo-oxygenase activity, on glycogenolysis was examined in the hepatocyte model. Ibuprofen (80 microM), indomethacin (50 microM) and meclofenamate (60 microM) all increased rates of glycogenolysis when added under basal conditions. In contrast, piroxicam (50 microM) had no effect on glycogenolysis in the hepatocyte system. Concentrations of ibuprofen below 80 microM did not significantly increase rates of glycogenolysis. Ibuprofen (80 microM) had no effect on glycogenolysis in the presence of 10(-5)M adrenaline or 5 X 10(-7)M glucagon, but did increase glycogenolytic rates in the presence of 5 X 10(-8)M glucagon. Ibuprofen-stimulated glycogenolysis was inhibited by addition of prostaglandin E2 (PGE2). Under conditions where glucagon-stimulated glycogenolysis was inhibited by exogenous PGE2, addition of ibuprofen (80 microM) increased the rate of glycogenolysis. Ibuprofen had no effect on basal or glucagon-stimulated hepatocyte adenylate cyclase activity. In conclusion, these results demonstrate that nonsteroidal anti-inflammatory drugs which are carboxylic acids can increase the rate of glycogenolysis in isolated hepatocytes. The high concentrations of drug required to stimulate glycogenolysis, the lack of effect of piroxicam, and the demonstration of stimulation by ibuprofen in the presence of exogenous PGE2 all suggest that the stimulation of glycogenolysis by ibuprofen, indomethacin and meclofenamate is independent of cyclooxygenase inhibition. These observations are consistent with reports that carboxylic acid nonsteroidal anti-inflammatory drugs can interfere with hepatic intracellular calcium handling.