Transport of 14 C-4-Cholesterol between Serum and Wall in the Perfused Dog Common Carotid Artery

The transport of certain materials between the blood and the wall in arteries appears to be dependent on wall shear rate with shear rate-enhancing flux; however, the mechanism is unclear. If the transport is diffusional, it must involve three steps: diffusion across a boundary layer, uptake at the blood-wall interface, and transport within the wall. If the first step is rate controlling, if wall shear rate is spatially uniform, and if a diffusion boundary layer commences upstream at the junction between the vessel and an impermeable tube, then flux will be proportional to the cube root of wall shear rate divided by distance and will depend on the species diffusion coefficient. A dog's common carotid artery was perfused with serum containing14 C-4-cholesterol linked with lipoprotein; the fluid mechanics resembled those described above. In 20 experiments, there was no spatial dependence of uptake of the label, flux was lower by a factor of about a hundred than that predicted, and there was a suggestion (statistically nonsignificant) of shear dependence. The first two findings are inconsistent with transport controlled by the diffusion boundary layer. An uptake-controlled transport could be shear dependent.