Tracer exchange in the normal and ischemic coronary circulation

Proper function of the coronary blood-tissue exchange system may be important in the preservation of myocardium threatened by ischemia. We have undertaken studies aimed at elucidating the functions of this system under baseline and ischemic conditions. The exchange of [14C]sucrose between the coronary capillaries and extravascular space has been studied with the multiple-tracer method. Protein transport has been examined by measuring the deposition of labeled albumin and by collecting cardiac lymph. Results indicate that reduced-flow ischemia decreases functioning capillary surface area but increases permeability to small molecules and protein. Hyaluronidase and adenosine can restore flow after partial occlusion of the coronary artery. However, only hyaluronidase restores capillary surface to its baseline value. Thus, ischemic effects on exchange are not controlled merely by hemodynamic factors. Reduced-flow ischemia in the heart can induce a vascular permeability change in the lung circulation. We conclude that capillary and interstitial transport are altered significantly by ischemia. Preservation of the proper function of these processes may be important in protecting the ischemic myocardium.