Autofluorescence of adipose tissue measured with fibre optics

The optical absorbance and fluorescence of porcine subcutaneous adipose tissue were measured directly with fibre optics. Either mercury or xenon light sources were used to illuminate tissue samples through one branch of a bifurcated light guide. Fluorescence was detected through the other branch of the light guide. Grating, prism and continuous interference filter monochromators were installed at appropriate locations in the light path and measurements were made with a computer-operated photomultiplier whose dynamic range was optimized at each wavelength measured. There was a small absorbance peak at 420 nm. With excitation at 365 nm, the peak of the fluorescence emission spectrum was at 510 nm with a secondary plateau from 430 to 450 nm. Proline powder and purified biochemical Type III collagen were also autofluorescent with a peak emission at 510 nm. Adipose cells associated with bovine heart valves were examined by fluorescence microscopy to obtain preparations containing adipose cells plus all three histological types of connective tissue fibres on the same section. Reticular fibres (around adipose cells) together with collagen and elastin fibres (in the heart valves) were all autofluorescent. It is suggested that the major source of adipose tissue fluorescence is from the reticular fibres that surround adipose cells, with minor contributions from other sources such as collagenous septa, vascular elastin and, possibly, cytoplasmic components.