Bone blood flow in the rat using arteriolar blockade: comparisons between labelled resin particles and microspheres

Arteriolar blockade is probably the most widely used laboratory method for bone blood flow measurement. At first, cheap labelled cationic resin particles were used. These have largely been displaced by labelled microspheres, which have theoretical advantages but are expensive. This investigation compares measurements of bone blood flow made with the 2 different materials, using a reference artery method. Resin particles (1.4 mg per rat) were compared with 2 different doses of 85Sr-labelled microspheres (1 mg and 3 mg per rat). Whole bone blood flow from the 3 groups was not statistically different. Regional bone blood flow comparisons using resin particles and 1 mg dose microspheres showed no significant difference in epiphyses or metaphyses. In the resin group, marrow flow was significantly lower, and cortical flow elevated. It is suggested that these differences are caused by leaching of 59Fe to plasma, and methods of preventing this are discussed. Measured flow rates were significantly increased in the tibial marrow and cortex using 3 mg microspheres, compared with the 1 mg dose. This increase may reflect better sampling of the arteriolar beds. We conclude there is little advantage in using microspheres for bone blood flow measurement. When sufficient resin particles of appropriate size are injected and procedures are adopted to prevent leaching of isotope to plasma, the observed measurements are essentially identical.