AJP - Heart and Circulatory Physiology, Vol 232, Issue 3 341-H347, Copyright © 1977 by American Physiological Society
Bone extraction and blood clearance of diphosphonate in the dog
S. P. Hughes, D. R. Davies, J. B. Bassingthwaighte, F. G. Knox and P. J. Kelly
The transcapillary extraction of diphosphonate, as [99mTc]EHDP, a substance
used in bone scanning and for management of certain metabolic bone
diseases, has been examined. The maximum instantaneous extraction for
[99mTc]EHDP was 0.27 +/- 0.05 (mean +/- SD, N = 10) and the net extraction
at 5 min was 0.18 +/- 0.05 (N = 10). The permeability ratio of [99mTc]EHDP
to the freely diffusible compound, sucrose, using the formula PS = -Fs loge
(1 - Emax), was 0.71. This is similar to the ratio of diffusion
coefficients of EHDP to sucrose, which is estimated to be 0.78. These
results suggest that the mechanism by which [99mTc]EHDP passes through the
capillaries in bone is passive diffusion. Tissue level estimations of EHDP
confirm a rapid blood clearance associated with an increase in the rate of
urinary excretion; the level of [99mTc]EHDP in bone, however, remains
constant. The fractional excretion of [99mTc]EHDP was 27.3 +/- 2.0% in
control dogs and was unchanged by thyroparathyroidectomy and subsequent
infusion of parathyroid hormone.
