Fig. 6.

a Biodistribution of ¹⁴C-D-luciferin in nude mice without fluc expression after tail-vein injection of 18.5 kBq ¹⁴C-D-luciferin and 3 mg carrier D-luciferin. Note the early high uptake values in the kidneys due to fast renal excretion of the tracer; 15 min after injection, significant uptake in most of the organs is demonstrated with low uptake in the brain. Blood levels and liver activity, which equals blood pool at early time points, peak early but fall rapidly. b Biodistribution of ¹⁴C-D-luciferin in nude mice without fluc expression after intraperitoneal injection with the same amounts of tracer and carrier like above. Note the differences in biodistribution after intraperitoneal injection in comparison to intravenous injection: Blood levels rise less high but are longer detectable. Kidney activity peaks later. In general, organ activity is not getting as high as after intravenous injection. Bowel/intestine activities are at early time points high probably due to the injection route