Comparison between fluorescein angiography and fluorescein microscopy.

Fluorescein angiography (FA), which implies that the tissue is reproduced in natural size, and fluorescence microscopy was compared in anesthetized normovolemic and hypovolemic rats in order to define the microscopic background to the fluorescence pattern obtained by FA. It was found that the fluorescence detected by FA by the use of sodium fluorescein as an indicator substance was emitted from the interstitial and intracellular compartments, including the intranuclear. Microscopy showed that sodium fluorescein was located extravascularly in the small intestine within 4 seconds after an intravenous injection. There was a 4 second interval between corresponding microscopic and macroscopic fluorescence pattern.