IMPROVEMENT OF ESTRADIOL 17-BETA-D-GLUCURONIDE CHOLESTASIS BY INTRAVENOUS ADMINISTRATION OF DIMETHYLETHANOLAMINE IN THE RAT

The intravenous administration of dimethylethanolamine in the rat promotes a selective enrichment of liver membranes with polyunsaturated phosphatidylcholines. The effect of dimethylethanolamine pretreatment on cholestasis induced by estradiol 17-beta-D-glucuronide, a potent cholestatic agent, was assessed in this study. Dimethylethanolamine, dissolved in sodium-taurocholate was infused intravenously (0.3 mg/kg/min) for 15 hr. One group of control rats (estradiol 17-beta-D-glucuronide controls) received the bile salt only. An estradiol 17-beta-D-glucuronide bolus was then injected intravenously (10.4 mg/kg) into dimethylethanolamine-pretreated and estradiol 17-beta-D-control rats, and its effect on bile flow and biliary lipid secretion was compared for 3 hr. The estradiol 17-beta-D-glucuronide inhibitory effect on bile flow and biliary lipid secretion was significantly antagonized by dimethylethanolamine pretreatment. The maximum inhibition of bile flow was found 30 min after estradiol 17-beta-D-glucuronide administration, when it decreased from 3.5 +/- 0.4-mu-l/min/100 gm (basal) to 0.9 +/- 0.3-mu-l/min/100 gm in estradiol 17-beta-D-glucuronide controls, whereas in dimethylethanolamine-pretreated rats this decreased only from 3.2 +/- 0.4 (basal) to 2.3 +/- 0.4-mu-l/min/100 gm. Bile flow and the biliary secretion of cholesterol, phosphatidylcholine and bile salts were significantly higher in the dimethylethanolamine-pretreated rats than in estradiol 17-beta-D-glucuronide controls (p < 0.02) during the cholestatic phase. The inhibitory effect of estradiol 17-beta-D-glucuronide on bile flow was associated with a marked decrease of membrane fluidity (p < 0.001) assessed by 1,6-diphenyl-1,3,5-hexatriene fluorescence anisotropy and with a cholesterol enrichment of microsomes, sinusoidal and canalicular liver plasma membranes and inhibition of sinusoidal Na+, K+-ATPase activity (p < 0.05). These membrane alterations persisted 180 min after estradiol 17-beta-D-glucuronide administration despite complete normalization of bile flow. Dimethylethanolamine pretreatment significantly counteracted the reduction of membrane fludity (p < 0.001), the cholesterol enrichment and the inhibition of Na+, K+-ATPase (p < 0.05) promoted by estradiol 17-beta-D-glucuronide administration in all membrane subfractions 30 and 180 min after administration. In addition, dimethlethanolamine-pretreated rats had more poly-unsaturated fatty acids in membrane phosphatidylcholine with respect to the control groups. Dilatation of canaliculi and loss of microvilli were evident in estradiol 17-beta-D-glucuronide controls 180 min after estradiol 17-beta-D-glucuronide administration. Dimethylethanolamine pretreatment antagonized the toxic effect of estradiol 17-beta-D-glucuronide cholestasis, particularly in the canalicular zone, which had a normal structure both 30 and 180 min after estradiol 17-beta-D-glucuronide administration. In conclusion, the intravenous administration of dimethylethanolamine improves the biochemical, biophysical and ultra-structural features of estradiol 17-beta-D-glucuronide cholestasis in the rat.