Effects of pentobarbital and cyproheptadine on brain ischemia induced by bilateral occlusions of carotid arteries and vertebral arteries of second cervical vertebra in rats

In vivo and in vitro evidence for ATP-dependency of P-glycoprotein-mediated efflux of doxorubicin at the blood-brain barrier

We investigated the role of ATP in the active efflux of doxorubicin (DOX) mediated by P-glycoprotein (P-gp), the multidrug-resistance (MDR) gene product, at the blood-brain barrier. In transient brain ischemic rats prepared with 4-vessel occlusion of vertebral and common carotid arteries for 20 min, a procedure that depleted their brain ATP content to 3% that of normal rats, the estimated permeability coefficient of DOX was increased 17-fold (to 243 +/- 2.5 microL/min/g brain). When the ATP content recovered to a normal level by means of 30-min and 24-hr cerebral recirculation of blood, the permeability coefficient recovered to 14.0 +/- 5.0 and 18.4 +/- 2.3 microL/min/g brain (mean +/- SEM, N = 3-6), respectively, very close to the control permeability (14.3 +/- 1.5 microL/min/g brain). The uptake of DOX by primary cultured brain capillary endothelial cells expressing P-gp at the luminal membrane was increased significantly (up to 2-fold), which correlated well with the decrease of cellular ATP contents caused by treating the cells with metabolic inhibitors. Evidence for the ATP-dependent transport of DOX obtained from the present in vivo and in vitro studies strongly indicates that P-gp in the brain capillaries functions actively as an efflux pump in the physiological state, providing a major mechanism to restrict the transfer of DOX into the brain.

In vivo evidence for ATP-dependent and P-glycoprotein-mediated transport of cyclosporin A at the blood-brain barrier

To evaluate the significance of P-glycoprotein (P-gp)-mediated active efflux on the blood-brain barrier (BBB) permeability of cyclosporin A (CsA) in vivo, we investigated the effects of ATP depletion in the brain and of a multidrug-resistant (MDR) reversing agent on the transport of CsA across the BBB. Using transient brain ischemia obtained by 4-vessel occlusion of vertebral and common carotid arteries in rats to deplete ATP content in the brain, the estimated permeability surface area product (PS) value of [3H]CsA was increased 2.7-fold compared with that in normal rats, whereas the PS value of [14C]sucrose was not altered. Additionally, when quinidine hydrochloride (QND) was infused into the brain through a microdialysis probe implanted in the rat hippocampus, the extravascular extraction of CsA was increased to approximately 2.5-fold of the control, whereas no difference in the extravascular extraction between control and normal rats having no implanted dialysis probe was observed. Furthermore, the efflux rate from brain to blood of CsA was decreased remarkably to 5% of control at steady-state by co-administration of CsA with QND directly into the brain through the dialysis probe. The ATP-dependent and QND-sensitive efflux of CsA from the brain strongly indicates that P-gp in the brain capillary endothelial cells functions as an efflux pump under the physiological state, and that P-gp-mediated efflux of CsA is a major mechanism of the restricted transfer from blood into the brain.