Highly sensitive spectrofluorimetric determination of trace amounts of lecithin using a norfloxacin-terbium probe.

BACKGROUND: Lecithin is found throughout biological systems. A new spectrofluorimetric method was developed for the determination of trace amounts of lecithin. METHODS: Optimum conditions for the determination of lecithin were investigated. RESULTS: Using norfloxacin (NF)-terbium ion (Tb3+) as a fluorescent probe, in a buffer solution at pH=6.80, lecithin reduced the fluorescence intensity of the NF-Tb3+ complex at lambda=545 nm; the reduced fluorescence intensity of the Tb3+ ion is proportional to the concentration of lecithin. The linear range and detection limit for the determination of lecithin were 1.08 x 10(-6)-3.02 x 10(-5) mol/l and 2.54 x 10(-7) mol/l. CONCLUSION: This method is simple, practical and relatively free of interference from coexisting substances, and can be successfully applied to assess lecithin in serum samples.

Distribution of terbium and increase of calcium concentration in the organs of mice i.v.-administered with terbium chloride.

To investigate the biological effects of terbium (Tb), male mice were intravenously administered with TbCl3 at 10, 25, or 50 mg Tb/kg. Time-course and dose-related changes in organ distributions of Tb were determined. More than 95% of the Tb in blood was in plasma, and the concentrations decreased rapidly. Contrary to normal pharmacokinetics, Tb concentrations in plasma were higher in the 10 mg/kg group than in the 50 mg/kg group. The concentrations after injection of 25 mg/kg were between 10 and 50 mg/kg injections. Tb was incorporated mainly in liver, lung, and spleen. In all groups more than 80% of Tb administered were found in these three organs. Disappearance of Tb in these organs was very slow. Tb was also found in kidney, heart and other organs. Coincidentally, it was found that the Ca concentration was increased in organs in which Tb was incorporated. After administration of Tb (50 mg/kg) the Ca concentration, compared to the controls, was 70-fold in spleen, 20-fold in lung, and 6-fold in liver. There were highly positive correlations between Tb and Ca concentrations in organs. Excretion of Tb in urine was 0.15-0.3% and that in feces was 1.7-12.5% for up to 7 days. These results indicate that liver, lung, and spleen are the main target organs of Tb administered intravenously, and that the increase in Ca concentrations is one of the important biological effects of Tb in target organs.

Interaction of terbium with human platelets.

The effect of terbium on platelets has been studied by aggregation experiments and by fluorescence measurements. TbCl3 does not substitute for CaCl2 in the aggregation of platelets induced by ADP, but it may even inhibit, probably by a competition mechanism. It was impossible to observe a sensitized emission of Tb3+ in the presence of platelets. Instead the lanthanide, like Ca2+, significantly increases the aggregation of platelets induced by A23187. The fluorescence yield of this compound is greater in the presence of platelets than in buffer alone. Energy transfer appears to take place from the aromatic amino acids of the platelet membrane to the bound ionophore.

Enhancement of Tb3+ fluoresence induced by serum proteins other than apotransferrin.

When Tb3+ ions are incubated with human serum, there is a large enhancement in the fluorescence of the Tb3+ ions as revealed by the excitation and emission wavelength pair 288 and 545 nm. The fluorescence enhancement represents the binding of Tb3+ ions not only to (apo)transferrin, but to albumin and gamma-globulins as well. Spectrophotometric evidence indicate involvement of tyrosyl residues at the cation binding site(s). The ion fluorescence induced by albumin and gamma-globulins invalidates the usefulness of the fluorometric determination of transferrin in the routine laboratory.