The Effect of Varying the Amount of Unlabelled 5,5-Dimethyloxazolidine-2,4-Dione(Dmo) in the Measurement of Rat Hepatic Intracellular pH Using [¹⁴C]DMO

1. Hepatic intracellular pH (pH_i) was measured in intact rats by distribution of 5,5-dimethyloxazolidine-2,4-dione (DMO), using [¹⁴C]DMO and a range of doses of unlabelled DMO, previously neutralized with sodium hydroxide.

2. Mean calculated pH; fell from 7·27 to 7·17 as the dose of added unlabelled DMO was increased from zero to 0·19 mmol/kg (25 mg/kg) and thereafter remained constant up to and including the highest dose group (1·55 mmol/kg; 200 mg/kg).

3. Control observations showed that the change in calculated pH_i with DMO dose could have been related to the consequential sodium load, rather than to the presence of a saturable process determining the distribution of DMO.

4. Reasons are given why it is nevertheless desirable to add carrier DMO when employing [¹⁴C]DMO for the measurement of hepatic pH_i in the rat.