Abstract
Radiolabeling of oxybutynin, a muscarinic acetylcholine (mACh) receptor antagonist agent with Tc-99m is of considerable interest for imaging of urinary bladder. This study is aimed to optimize radiolabeling yield of oxybutynin with Tc-99m using SnCl2 center dot 2H(2)O as a reducing agent with respect to factors that affect the reaction conditions such as oxybutynin amount, stannous chloride amount, reaction time and pH of the reaction mixture. In vitro stability of the radiolabeled complex was checked and it was found to be stable for up to 8 h. Tc-99m-oxybutynin was injected via subcutaneous and intravenous administration routes into normal Sprague-Dawley rats. Biodistribution studies have revealed that Tc-99m-oxybutynin exhibits high affinity and specificity for the muscarinic M-3 subtype located on the smooth muscle of urinary bladder relative to the M-1 and M-2 subtypes of the G protein coupled receptor (GPCR) superfamily. In vivo uptake of subcutaneous Tc-99m-oxybutynin in urinary bladder was 19.6 +/- 0.42% ID at 0.5 h, whereas in intravenous administration route the accumulation in the urinary bladder was found to be 9.4 +/- 0.31% ID at 0.5 h post injection. Administration of cold oxybutynin effectively blocked urinary bladder uptake and further confirms the high specificity of this complex for the M-3 receptor.