Characterization of the corticosteroid-binding globulin response to decidualization in the hamster

We sought to characterize the relationship between the decidualized uterus and circulating corticosteroid-binding globulin (CBG) levels during pseudopregnancy in the hamster. Blood CBG levels (as measured by [3H] cortisol binding) averaged 11-fold greater for decidualized hamsters than for sham-operated controls on day 8 of pseudopregnancy (PSP). We used sequential blood sampling from individual hamsters to monitor changes in CBG content after decidualization. The increase in blood CBG after decidualization was rapid, as evidenced by a significant difference in CBG content between sham-operated and decidualized groups within 24 h after surgery. We varied the extent of uterine traumatization to induce differing amounts of decidual tissue. Regardless of the amount of decidual tissue, all decidualized hamsters showed a significant increase in blood CBG; however, there was a dose-dependent relationship between the amount of decidual tissue formed and the magnitude of the CBG response. We used hysterectomy (on PSP day 6, after decidualization on PSP day 4) to determine if removal of the decidualized uterus influenced the duration of the CBG response. Bilateral hysterectomy blocked further increases in blood CBG, whereas in control animals (unilateral hysterectomy) blood CBG continued to increase after surgery. Thus, once the CBG response is initiated, the decidualized uterus is necessary to maintain elevated CBG levels. The findings in this study provide further evidence for the presence of a decidua-hepatic endocrine axis that appears to be responsible for elevation of circulating CBG levels during early pregnancy in the hamster.