ON THE SOURCE OF THE OSCILLATIONS OBSERVED DURING IN-VIVO ZINC PHTHALOCYANINE FLUORESCENCE PHARMACOKINETIC MEASUREMENTS IN MICE

Surface-detected fluorescence spectroscopy can be used to monitor the pharmacokinetics of uptake and clearance of red-absorbing fluorophores such as zinc(II) phthalocyanine (ZnPc) in vivo. When this technique i s applied to mice that have been fed on a normal chlorophyll-based die t, and particularly when measurements are performed in the abdominal r egion, oscillations are sometimes observed superimposed on the pharmac okinetic curve of the ZnPc. An oscillatory signal has also been observ ed arising from the abdominal region of control mice fed a normal diet but not injected with the ZnPc photosensitizer; this oscillatory comp onent to the signal is reduced when mice are fed a chlorophyll-free di et. The oscillatory signal component has been attributed to fluorescen ce arising from chlorophyll derivatives (pheophorbide/pheophytin) cont ained in the rodent food, whose concentration in the measured abdomina l region changes substantially with time, presumably due to digestive processes. Thus it is important to be aware of the possibility of such artifactual contributions to In vivo fluorescence pharmacokinetic mea surements.