Maintenance of plasma-derived proteins at much lower concentrations in the uterine lumen of the rabbit: a kinetic study of passage.

Human serum albumin (HSA) and human gamma globulin (HGG) in serum and uterine fluid of nonpregnant rabbits at various times after an i.v. injection (100 mg/kg) were measured by a radial immunodiffusion test using specific antisera. The HSA concentration in uterine fluid rose to a peak at 12 hr when it was 11% of the serum concentration and then declined, whereas HGG reached a peak at 18 hr (3.2% of serum level) and decreased thereafter. The HSA passed 2 1/2 times faster than HGG, but both proteins equilibrated with uterine fluid in about 12-18 hr. Steady state levels of HSA and HGG indicated that uterine fluid: serum ratios were 1:10 and 1:20, respectively. Similar ratios were found for total protein and rabbit serum albumin (1:10) and rabbit gamma globulin (1:20). Therefore, except when there is a local immune response, the uterine lumen contains only about 5% of the serum antibody concentration. Available data in the mouse, rat and dog also indicate disparity between serum and uterine fluid protein levels.