Uptake and biliary excretion of Cu64 in rabbits in relation to blood ceruloplasmin.

Abstract

It has been postulated that one of the important biological functions of the alpha-2 globulin, ceruloplasmin, is the regulation of the biliary excretion of inorganic copper(1). However, there is little experimental evidence to support this theory(2,3). With the availability of an experimental technique for modifying the blood ceruloplasmin levels(4), it became feasible to reexamine the problem as to possible correlations between serum ceruloplasmin, liver uptake, and biliary excretion of Cu64 in the rabbit. Three groups containing 9 to 12 male albino rabbits (12-13 weeks old) were employed. One group was maintained for 10–15 days on a commercial dry ration containing molybdate-sulfate, a diet known to reduce ceruloplasmin levels in the rabbit and greatly elevate total blood copper(4,5). A second group, which served as controls, was maintained on the commercial ration without added salts. A third group was maintained on a ration mixed with inorganic copper, 0.005% copper as Cu2SO4 for 4 weeks in order to elevate serum ceruloplasmin levels (5,6). Ceruloplasmin was measured as p-phenylenediamine oxidase activity in each rabbit serum 24 hours before administration of the isotope(7). Animals were given an intravenous injection of 75 microcuries of high activity Cu64 acetate (6 μg copper) via the marginal ear vein and sacrificed 2, 25, and 50 hours later. Levels of Cu64 activity were measured in 0.1–0.5 ml of bile immediately withdrawn from the gall bladder. Suitable samples of liver and cross sections of cortex and medulla of the kidney were hydrolyzed with sulfuric, perchloric and nitric acids(8). Each sample was returned to a standard volume and Cu64 activity determined. The values obtained were corrected for radioactive decay and expressed as percent of the dose administered (Table I). Radioactive copper was determined in a well-type, thallium-activated sodium iodide crystal scintillation counter. In those rabbits maintained on a high molybdate-sulfate diet there resulted a marked diminution of serum ceruloplasmin levels, uptake of Cu64 by liver, and excretion of copper at 2, 25, and 50 hours (Table I). Cu64 uptake by liver in this group was reduced to 35.7% of the control level 2 hours after injection. Along with a 20% reduction in serum ceruloplasmin, the biliary excretion of Cu64 was virtually zero. This sharp suppression in liver uptake and biliary copper excretion in 2, 25, and 50 hours occurred despite an elevation in the non-ceruloplasmin copper pool(4,5). On the other hand, a significant increase in the concentration of Cu64 in the kidney was noted in this group as compared to the other 2 groups.