Abstract

PIP: In an effort to explain the mechanism of the increased efficacy of the copper-releasing IUD, the in vitro action of copper ions on the polysome patterns of rabbit endometrium and liver was studied. The uterine horns were extracted from female rabbits with prior sexual experience. The horns were sliced longitudinally, and the endometrium carefully scraped off with a curette. For each experiment the scrapings from 4 to 6 cornua were pooled, suspended in buffer A (.14 M sucrose containing .05 M Tris-hydrochloride, .05 M potassium chloride, .005 M magnesium chloride, 200 mcg/ml heparin and brought to pH 7.6), and divided into 5 equal fractions. To 4 of the fractions, copper (as copper chloride) was added to reach final concentrations of .15, 13, 1, and 1.5 mM, respectively. The fifth fraction served as a control with no copper added. The liver was extracted, homognized in buffer A, and treated in the same way as the endometrium. The homogenates were further adjusted, treated, centrifuged, and analyzed. Results showed that the in vitro addition of copper in concentrations as low as .15 mM produced a significant decrease in the amount of polysome aggregates that could be recovered from endometrium. Liver required concentrations of at least .3 mM to show a similar effect. For concentrations of 1.5 mM copper, the recoverable amount of the polysome fraction from liver and endometrium was 40% and 25%, respectively, of that recoverable without added copper. When the obtained polysomes were analyzed in a sucrose gradient, additions of increasing concentrations of copper induced a progressived decrease of the heavy components of the polysome patterns with a concomitant increase in the lighter components. The results which show copper as a possible dissociating agent of liver polysomes are important, but it is doubtful that liver concentrations of those required to dissociate polysomes (.3 mM) will ever be reached by the use of these IUDs. It is postulated that the impairment in polysome aggregation is part of the mechanism of the copper IUD, and it may modify both the endometrial characteristics and the blastocyst viability required for successful embryo development.