Dynamic monitoring of total-body absorption by 19F NMR spectroscopy: one hour ventilation of HFA-134a in male and female rats.

Six male and six female Sprague-Dawley rats were ventilated head-only for 1 h on a 15% atmosphere of 1,1,1,2-tetrafluoroethane (HFA-134a) in air in a magnetic resonance imaging spectrometer. Results from these dynamic 19F NMR studies suggest that a steady-state in vivo concentration of HFA-134a was approached at approximately 25 min into the exposure. Quantitative integration analysis using an external standard estimated this plateau to be 58.3 +/- 11.9 mg of absorbed HFA-134a per rat. The HFA-134a 19F NMR signal disappeared rapidly following removal of the test atmosphere, with an elimination half-life of 4.6 +/- 0.6 min in the male rats and 4.9 +/- 1.5 min in the female rats. The data suggest that there was no statistical difference between the sexes in amount absorbed or in elimination half-lives.