Introduction: The use of fluorescent microspheres (FM) to determine regional blood flow is increasingly common. Estimation of blood flow requires tissue digestion with dye extraction and spectroscopy. Incomplete recovery of microspheres will underestimate values for organ blood flow. Using the method of Chien et al (Cardiovasc Res 1995; 30: 405) we have assessed organ-specific FM recovery in 33 adult rats. Methods: A standardised aliquot of green FM, not used in vivo, was added to each tissue sample prior to processing. Samples were digested in 4M potassium hydroxide (KOH) and FM extracted by vacuum filtration. Dye was extracted using Carbitol® acetate and fluorescence determined. The fluorescence intensities of 5 aliquots of green FM were averaged to give the value for 100% recovery. Results: mean ± SD.
| Organ | % recovery | Organ | % recovery | Organ | % recovery |
|---|---|---|---|---|---|
| Heart | 89±12 | Hindbrain | 89±10 | Spleen | 91±11 |
| Lungs | 89±17 | Duodenum | 90±11 | Liver | 92±16 |
| Kidneys | 91±15 | Jejunum | 89±11 | Diaphragm | 88±12 |
| Adrenals | 91±13 | Ileum | 89±12 | Sk. muscle | 90±11 |
| Cortex | 89±11 | Colon | 93±19 |
Conclusions: No significant differences were found between organ samples despite concerns about incomplete digestion of fatty tissue by KOH. Use of an internal standard allows correction for FM loss during extraction or inaccurate addition of solvent for dye extraction.