Effect of plasma proteins on buprenorphine transfer across dually perfused placental lobule

Objective. The aim of this investigation is to determine the effect of human serum albumin HSA and α-acid glycoprotein AAG on buprenorphine BUP transplacental transfer and distribution. Methods. The technique of dual perfusion of placental lobule DPPL was utilised. BUP was co-perfused with the marker compound antipyrine AP. In each experiment, the radiolabelled isotopes ³H-BUP and ¹⁴C-AP were added to enhance their detection limits. Human plasma proteins, HSA and AAG, were added to both the maternal and fetal circuits separately and in combination at their physiological concentrations in maternal and fetal circulations close to term. Results. Transplacental transfer of BUP, in absence of plasma proteins, is a two-step process: the first is its uptake by the syncytiotrophoblast from the maternal circuit, and the second is its transferrelease from the tissue to the fetal circuit. The addition of HSA to the perfusion medium affected only the second step of BUP transfer, but AAG affected both steps. The combined effect of HSA and AAG was not different from that observed in presence of the latter alone. Conclusions. Binding of BUP to circulating AAG could have an important role in the transfer of the drug from the maternal to fetal circulation.