Studies on bile secretion with the aid of the isolated perfused rat liver I. Inhibitory action of sporidesmin and icterogenin

Abstract

An isolated perfused rat liver preparation has been developed to aid the study of the mechanisms underlying the secretion of bile and the cholestatic actions of two naturally occurring agents, icterogenin and sporidesmin. The perfused liver produced bile for 3-5 h at a steady rate slightly above that observed in intact rats possessing external biliary cannulae. During this period of perfusion detailed biochemical and physiological studies on the behaviour of the liver were carried out. Morphological examination of the livers after several hours of perfusion was performed by means of electron microscopy and quantitative analysis of the pictures for certain structural elements has been performed. The addition of ethanol (final concentration 27 mM) to control perfusion had no significant effect on bile flow or liver morphology except that there was a decrease in the numbers of multi- and mono-vesicular bodies and in their relative proportions in the cytoplasm. There was a large though transient increase in perfusate lactate to pyruvate ratio and a sharp fall in the perfusate pH. Sporidesmin (2 mg in ethanol-buffer solution) rapidly decreased bile flow, and retarded the increase in the lactate to pyruvate ratio and the decrease in the pH of the perfusate seen in ethanol controls. Electron micrographs of the livers following sporidesmin administration showed large regions of the bile canaliculi devoid of microvilli and there was the appearance in the cytoplasm of lysosomal-like structures containing numerous glycogen granules. Icterogenin (4 mg in ethanol-buffer solution) produced a rapid cholestasis, inhibited the changes in the lactate to pyruvate ratio and the perfusate pH seen in the ethanol control preparations. Electron micrographs of the icterogenin-treated livers revealed changes in the canalicular membrane, extrusion of material into the canalicular lumen and aggregation of lysosomes in the cytoplasm. These studies suggest that bile flow in the rat is seriously affected by disturbances to the canalicular membrane, and preliminary biochemical investigations of these disturbances are reported here.