Mechanics of Bile Secretion

Abstract

In the isolated perfused rat liver prepn., bile flow in a vertical catheter continues at a steady rate from bile pressures negative with respect to the liver to bile pressures within 3 or 4 cm. of the max. attainable. Subsequently, bile flow drops rapidly to zero. The limiting bile secretion pressures thus detd. are consistently greater than the perfusion pressures throughout the physiological and sub-physiological range. Bile flow is a function of blood flow through the liver, falling sharply if blood flow rates in the isolated liver decrease below 10 cc./min. Bile flow rate can vary over a wide range without affecting max. bile secretion pressures. At bile pressures exceeding the max. secretion pressure, disappearance of bile from the biliary tree was demonstrated. Bile pressure and rate of backflow were related. The capacity of the biliary tree considered as an elastic reservoir was measured by changing bile secretion pressures and observing the extra vols. of bile appearing when bile pressures are made negative. The max. reservoir capacity thus demonstrated was the vol. of bile formed in 2 min. Bile production ceases at approx. 25[degree]C and is max. between 38-40[degree]C. Q10 averages 4.5 for the temp. range from 28-38[degree]C, 3.3 between 30 and 40[degree]C. Apparently bile formation involves active secretion supported by metabolic energy and is not based entirely on a filtration- reabsorption mechanism process: the max. bile secretion pressure probably is detd. by the critical pressure at which leaks appear in the biliary tree; therefore, the max. biliary secretion pressure is a measure of mechanical properties of the liver. In the rat, the capacity of the biliary tree to function as a reservoir, in lieu of the absence of a gall bladder, is extremely limited.