Figure 5
Absorbance of the plasma and H 2 S concentrations. Panel A, absorbance spectra of the plasma collected at the end of the overall bleeding period in control (open circles) and vitamin B12-treated (closed circles) rats. There was a clear peak of absorbance at 525 nm in vitamin B12-treated rats corresponding to a vitamin B12 plasma concentration of 185 ± 216 μM/l. No peak was observed in any of the control rats. At 670 nm, that is, the absorbance wavelength of the methylene blue, no peak was observed, neither in control nor in the vitamin B12-treated rats. Panel B, absorbance spectra, between 400 and 700 nm, of the plasma of the control rats, before (open triangles) and at the end of the bleeding period (closed squares). The observed absorbance values at 670 nm would theoretically correspond to a H2S concentration of around 4 μM/l in the dilute plasma (or 8 μM/l in the plasma, see text for additional comments), as illustrated using a control solution (phosphate-buffered saline, PBS) containing H2S (4 μM) (open diamonds). The lack of peak of absorbance in the plasma at 670 nm along with the pattern of absorbance over the visible spectrum (continuous decrease of absorbance from 400 nm) strongly suggest that it is the turbidity of the medium which could account for this apparent presence of H2S in the plasma.