Journal of Applied Physiology, Vol 39, Issue 4 596-602, Copyright © 1975 by American Physiological Society
Strontium-85 extraction during transcapillary passage in tibial bone
R. H. Cofield, J. B. Bassingthwaighte and P. J. Kelly
Indicator dilution experiments were done to determine the extraction of
85Sr during a single passage through capillaries of the tibial diaphysis.
Extraction was estimated by injection of 85SrCl2 and a nonpermeant,
reference tracer, T-1824-labeled albumin, into the nutrient artery and
recording of the effluent venous dilution curves (femoral vein). The mean
(+/- SD) maximal instantaneous extraction was 0.53 +/- 0.08 (N = 12). Net
retention after 10 min, estimated from venous curves, was 0.41 +/- 0.06 (N
= 12), which appeared not substantially different from the retention
estimated by direct isotope counting of the tibias for 85Sr, 0.35 +/- 0.06
(N = 12). In a second set of experiments in intact animals, tibial 85Sr
extraction after intravenous injection was apparently higher, 0.53 +/- 0.28
(N = 15). Values of tibial diaphyseal blood flow, estimated from washout
curves for iodoantipyrine after tibial nutrient artery injection, were 1.47
+/- 0.63 ml/min per 100 g (N = 27). The extraction was not much diminished
by higher flows. The estimates of permeability-surface area product (PS)
for bone capillaries did increase with flow, suggesting recruitment of more
capillaries at higher flows. PS values averaged 0.63 +/- 0.29 (N = 12); we
conclude that the capillary membrane is a primary barrier to the passage of
85Sr and presumably other small hydrophilic solutes.
