Relationship between low intensity shear stress, aortic histamine formation, and aortic albumin uptake

The relationship between aortic histamine forming capacity (HFC) and aortic albumin uptake, as measured through fluorometric determination of the intraaortic content of bovine serum albumin conjugated to fluorescein isothiocyanate (FITCBSA) under steady-state conditions has been examined in relationship to the applied mean shear stress intensity created by pulsatile perfusion of rabbit aortas with platelet-free blood for a 1-hr period. HFC and FITCBSA determinations were made on aortic segments exposed to entrance and exit flow conditions as well as on those segments in which flow was stable; mean shear stresses in the latter ranged from 7 to 21 dynes/cm 2. Regression analyses between the HFC and intraaortic FITCBSA content yielded the equation y = 0.41x + 38.6, r = 0.81 ( P < 0.005), where y = HFC and x = FITCBSA. These results indicate that the local rate of aortic histamine formation may influence local wall permeability to blood-borne macromolecules such as albumin; they also suggest that de novo histamine synthesis, mediated via the aortic histidine decarboxylase system, may have the potential of coupling altered hemodynamic states with subsequent alterations in wall resistance to macromolecule penetration and, as such, may have important ramifications with respect to vascular wall permeability increases involved in the initiation of atherosclerosis.