Reaction of metallic copper with biological substrates.
Copper intrauterine devices (IUDs) weigh less after removal from the human uterus due to interaction of metallic copper with various biological substrates. 400 sq. mm of electrolytic grade copper foil was placed in a mixture of .5 ml human uterine secretion and 2 ml of saline. After 18 h at 37.5 degrees C this material was lyzed and no longer viscous; a precipitate had formed and the copper strip was blackened. The cupric ionsconcentration in the solution was .0018 M. A similar incubation in 2.5 ml of saline alone yielded a cupric ion concentration of .00004 M. When the copper was incubated in a pH 8 buffer the corrosive action was slight as with saline. The amount of copper dissolved by the uterine secretion (1 ml/day) calculated for a 200 sq mm copper surface amounts to 60 mcg/day. When 1.8 ml of secretion was incubated with 400 sq mm without saline, lysis was shown and a cupric ion concentration of .01 M resulted. Bovineserum albumin served as a model substrate. The rate of dissolution of copper increased with increasing salt and albumin concentration. Copper immersed in albumin solution became dull due to preciptated protein on its surface, the portion of the strip extending into the air remained shiny, but a thin line at the interface became black suggesting that oxygen plays a role in the dissolution process. When oxidized .01 M glutathione was incubated with copper, cupric ions were formed; with reduced gluthathione, only a slight reaction occurred indicating the disulfide bond is a critical group in the copper dissolution process by biological materials. Turbidity, being a function of albumin concentration, arises from the precipitation of albumin by cupric ions which can be reversed at high albumin concentrations suggesting once cupric ions are formed, there is little competition for these ions. The finding that disulfide bonds oxidize metallic copper suggests ways by which the copper IUD might act: precititate albumin and change the uterine wall, reduce stickiness of secretions, lyse nucoid materials, inactivate enzymes, and kill sperm with cupric ions.