Transient blood-brain barrier passage of polar compounds at low pH.

The brain uptake index (BUI) of polar 14C-labeled test compounds with molecular weights (MWs) of 79-70,000 was examined using the single-pass carotid injection technique in pentobarbital-anesthetized rats. Compounds were injected in 40 mM malonate, pH 2.5, and 10 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid, pH 7.

Terminal endothelial cells of lymph capillaries as active transport structures involved in the formation of lymph in rat skin.

Electron microscopic examination of lymph capillaries of the dermal papillae of rat scalp skin revealed continuous extension of the lymph collection system into 4 to 10 micron diameter lumen capillaries with thin walls, scant basement lamellae (membranes), and blind-endings of 1 to 4 micron lumen diameter within endothelial-type cells. These terminal endothelial cells also displayed intracytoplasmic channels and pinocytotic vesicles, extensive cytoplasmic processes and a high cytoplasmic volume-percent of mitochondria suggesting active transport capabilities of lymphatic endothelia. The mitochondrial cytoplasmic volume-percent (mean 14.

Field dependent transverse relaxation rate increase may be a specific measure of tissue iron stores.

The degree to which MRI magnet field strength affects measured transverse relaxation rates (R2) defines a measure termed the field dependent R2 increase (FDRI). We report here the results of in vivo and in vitro experiments that were conducted to evaluate whether FDRI is a potentially useful measure of tissue iron stores. T2 relaxation times were obtained using two clinical MRI instruments operating at 0.