[The aminopyrine respiratory test under the acute effect of ethanol. Evaluation of a new method for the measurement of microsomal functions of the liver].

Microsomal demethylation, a partial function of the liver, can be estimated by the aminopyrine breath test. Both the determination of specific activity and the disappearance rate constant for 14CO2 in breath demand the assumption of rapid formaldehyde oxidation to CO2. Conversely, the disappearance of aminopyrine from plasma reflects microsomal aminopyrine metabolism only. Ethanol is known to affect both microsomal demethylation and formaldehyde metabolism. If in the presence of ethanol the latter process should become rate-limiting, a discrepancy between the data obtained in breath and in plasma could be expected. In order to investigate this possibility 10 fasting healthy male volunteers received 9 mg/kg (dimethylamine-14C)-aminopyrine (2 muCi) orally and, 3 hs later, 0.7 g/kg ethanol. Immediately following ethanol the specific activity of 14CO2 in breath decreased by 25% (p less than 0.005) and the disappearance of 14CO2 from breath was 31% lower than in 17 matched controls (p less than 0.005). The aminopyrine plasma disappearance rate, determined by GLC, decreased by 30% after ethanol (p less than 0.05). Since the decrease in aminopyrine plasma disappearance rate seems to account for the proportional decreases obtained by breath analysis, it is concluded that the aminopyrine breath test expresses the rate of microsomal demethylation even during altered formaldehyde metabolism, e.g. in acute ethanol intoxication.