Transcapillary adenosine transport and interstitial adenosine concentration in guinea pig hearts

Abstract

We used the multiple-indicator-dilution technique to observe the capillary transport of adenosine in isolated Krebs-Henseleit-perfused guinea pig hearts. Tracer concentrations of radiolabeled albumin, sucrose, and adenosine were injected into the coronary inflow; outflow samples were collected for 10-25 s and analyzed by high-performance liquid chromatography (HPLC) and by gamma- and beta-counting. The albumin data define the intravascular transport characteristics; the sucrose data define permeation through interendothelial clefts and dilution in interstitial fluid (ISF). Parameters calculated from adenosine data include permeability-surface area products for endothelial cell uptake at the luminal and abluminal membranes and intraendothelial metabolism. We found that in situ endothelial cells avidly take up and metabolize adenosine. Tracer adenosine in the capillary lumen is twice as likely to enter an endothelial cell as it is to permeate the clefts. There was no adenosine in the arterial perfusate. Under control conditions, the steady-state venous adenosine concentration was 3.6 +/- 0.8 nM, which from the flow and the parameters estimated from the tracer data gave a calculated ISF concentration of 6.8 +/- 1.5 nM. During dipyridamole infusion (10 microM) at constant pressure, the cell permeabilities went essentially to zero, whereas the venous adenosine concentration increased to 44.0 +/- 12.6 nM, giving an estimated ISF concentration of 191 +/- 53 nM. With constant flow perfusion, venous concentration during dipyridamole infusion was 30.9 +/- 6.3 nM, and estimated ISF concentration was 88 +/- 20 mM. We conclude that in this preparation, at rest, the ISF adenosine concentration is about twice the venous concentration and the ISF adenosine concentration increases with dipyridamole administration.

Quantification of Extracellular and Intracellular Adenosine Production

“…Similar model analyses conducted in a previous study on the same experimental model 20 revealed interstitial adenosine concentrations of 6.8 nmol/L under control conditions (our estimate, 34 nmol/L) and 191 nmol/L during membrane transport block by dipyridamole (our estimate, 94 nmol/L). Specific differences from the present study were as follows.…”

SENSOP: A derivative-free solver for nonlinear least squares with sensitivity scaling

“…The total number of trial parameter vectors calculated to obtain the fit was 11. The values of the parameter estimates are similar to those obtained by Wangler et al (18) in similar experiments.…”

“…Near the solution for small residuals, the right hand side of Eq. 18 below is an approximation to the covariance matrix, (18) Based on the approximation, the 95% confidence interval for the parameter θ j , will be (19) where t m-p,0.95 is the Student's t-distribution with m -p degrees of freedom (17).…”

“…An example of a common type of waveform obtained by positron emission tomographic imaging of tracer glucose ( 11 C-D-glucose or 18 F-deoxy-D-glucose) is the tracer content within an organ or a region of an organ following an injection into the circulation upstream to the inflow. A noise-free tracer residue function curve, R(t), mimicking a 180-s set of data was generated by an input function and a model system.…”

Interstitial adenosine: The measurement, the interpretation

“…Methods for estimating the whole heart average myocardial interstitial adenosine from measures of flows, from membrane and capillary wall permeabilities, from volumes of distribution, and from the venous outflow adenosine concentrations (Bassingthwaighte et al, 1985;Wangler et al, 1989;Gorman et al, 1991) are also indirect, but do attempt to take into account the known and measurable flow heterogeneities.…”