title: Capillary diffusion capacity for Cr-EDTA and cyanocobalamine in spontaneously beating rat hearts.
abstract: In order to obtain a functional estimate of the diffusional capacity of the myocardial capillary bed, the permeability surface area product (PS) for Cr-EDTA (mol. wt = 341) and cyanocobalamine (vitamin B12, mol. wt = 135) was determined in spontaneously beating Langendorff-perfused rat hearts over a wide range of coronary flow rates (700-3000 ml min-1 100 g-1). PS was determined by a single injection, colorimetric indicator dilution technique, allowing multiple, rapid and accurate determinations to be made in the same heart. During maximal vasodilation with nitroprusside Na PS averaged 535 +/- 33 and 220 +/- 22 ml min-1 100 g-1 for Cr-EDTA and vitamin B12 respectively at the highest flow (2917 +/- 74 ml min-1 100 g-1). The vasculature of the heart was found to be highly heterogeneous, since PS increased with flow and there were marked variations of extraction over transit times. A functional estimate of 'equivalent pore radius' was obtained from the ratio PSCr-EDTA/PSB12, which was 2.61 +/- 0.15 demonstrating a marked restriction to diffusion corresponding to a pore radius of 51 (41-75) A. This value is similar to that from skeletal muscle determined by the same method while PS-values are 40-45 times higher in the heart (Haraldsson & Rippe 1986). Taken together with morphological estimations of capillary surface area and endothelial path depth, these data indicate a 3-fold increase in the density of pores available for diffusion in the myocardium, compared to skeletal muscle.
authors.affiliation: Department of Physiology, University of Göteborg, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Wåhlander
authors.forename: P
authors.initials: P
authors.lastname: Friberg
authors.forename: B
authors.initials: B
authors.lastname: Haraldsson
mesh_terms: D000818:Animals; D002199:Capillary Permeability / Q000502:physiology*; D003331:Coronary Vessels / Q000502:physiology; D004058:Diffusion; D004492:Edetic Acid / Q000493:pharmacokinetics*; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009929:Organ Size / Q000502:physiology; D010477:Perfusion; D051381:Rats; D017208:Rats, Wistar; D014664:Vasodilation / Q000502:physiology; D014805:Vitamin B 12 / Q000493:pharmacokinetics*
chemical_list: D007202:Indicators and Reagents; D004492:Edetic Acid; D014805:Vitamin B 12