COMPARISON OF QUANTITATIVE WHOLE-BODY AUTORADIOGRAPHIC AND TISSUE DISSECTION TECHNIQUES IN THE EVALUATION OF THE TISSUE DISTRIBUTION OF [C-14] DAPTOMYCIN IN RATS

Quantitative whole-body autoradiography (QWBA) was evaluated and compa red to tissue dissection/liquid scintillation counting (TD/LSC) techni ques by determining the tissue distribution of radiocarbon in rats fol lowing iv administration of the antibiotic [C-14]daptomycin (LY146032) . QWBA, using computer-assisted video-image analysis, was initially ev aluated by characterizing and calibrating commercial standards to bloo d and brain, kidney, liver, and lung homogenates. Frozen (carboxymethy l)cellulose blocks containing tissue homogenates spiked with [C-14]glu cose (370-37 000 Bq/g or 10-1000 nCi/g) were sectioned and optical den sities (OD) measured. Characterization of QWBA included repeated measu res data analysis to determine the significance of tissue type and int ra- and inter-section and block variability. Regression models relatin g OD to radiocarbon concentration were also used to calibrate commerci al standards for use in QWBA analyses. Results indicated that there we re no substantial differences between OD readings from different tissu es; however, the greatest source of variation in OD reading was sectio n thickness. Because quantitative variations were largely attributed t o section thickness, an internal standard (IS), consisting of liver ho mogenates spiked with [C-14]glucose, was evaluated as a correction fac tor. Tissue concentrations of radiocarbon in male Fischer 344 rats wer e evaluated by QWBA and TD/LSC techniques 0.25 h following a single iv 10 mg/kg dose of [C-14]daptomycin. Results indicated that tissue conc entrations of radiocarbon obtained by QWBA, normalized using an IS, we re comparable to those obtained by TD/LSC.