A rabbit model to study the biokinetics of radiopharmaceuticals in bone

A technique is described using the rabbit as the 'animal model' to measure the rate of extraction of the bone-seeking agent, technetium labelled ethane-1-hydroxy-1, 1-diphosphonate (99Tcm-EHDP) following constant-rate infusion into the femoral nutrient artery. The extraction is shown to be approximately linear for a period of 60 min. Washout of the tracer from bone was followed for a further 60 min period and graphical analysis shows that each curve could be resolved into two distinct exponential functions. The 2-h residue of 99Tcm-EHDP in bone has been examined and is found to be dependent upon its route of administration. A high residue (43.7 +/- 5.1%) results when the infusate is delivered directly into the nutrient artery and the single muscular branch is tied off. Retrograde infusion via the femoral artery results in a lower residue (7.8 +/- 2.3%). The close correlation of these results in the rabbit with our previous findings in the dog suggested that the rabbit model described can be used to study the kinetics of other radiopharmaceuticals during their passage through bone.