Sulfonamide Acetylation in Isolated Rat Liver Cells

Abstract

Primary suspensions of isolated liver cells, prepared from rat livers perfused with Ca++ free buffer and 0.05% collagenase, were used for studies of sulfadimidine and sulfanilamide uptake and metabolism at various temperatures (29°–41°) and pH (6.4–7.8). The intracellular: extracellular ratio for sulfanilamide was found to be insensitive to both temperature and pH variations, while the corresponding ratio for sulfadimidine was pH dependent but insensitive to temperature variation. Decreasing pH increased the cell content of sulfadimidine. Sulfanilamide was metabolized by acetylation only, while sulfadimidine gave rise to several metabolites. The rate of sulfanilamide acetylation in primary cell suspensions was of the same order of magnitude as the acetylation rate of sulfanilamide published previously for the intact organ. Sulfanilamide was acetylated at the highest rate in the pH‐region from 7.0 to 7.5, while sulfadimidine was metabolized most rapidly between pH 6.7 and 7.3. At pH 7.5 sulfadimidine was metabolized at a rate only 35% of the rate at pH 7.3. The acetylation rate of both drugs increased with increasing temperature, approximately 5% per degree celcius, and exhibited a Q10 of 1.5.

Interaction between Drug Acetylation and Ethanol, Acetate, Pyruvate, Citrate, and L(minus;)Carnitine in Isolated Rat Liver Parenchymal Cells

“…Since pH variations of the incubation medium may change the acetylation rate, as reported for procainamide in this report (fig. I), and for sulfanilamide and sulfadimidine in a previous report (Olsen & Merrland 1981), it seems necessary with close pH control when studies on drug acetylation in isolated rat liver cells are performed. Due to the findings that both procainamide and sulfanilamide acetylation are pH dependent, the decreased medium pH caused by ethanol treatment, may probably abolish a stimulating effect of ethanol or ethanol metabolites.…”

“…It has been reported that addition of ethanol to the medium may lower the intracellular p H more than addition of acid (Merrland et al 1973), and it is therefore reasonable to assume that the medium pH recorded in the ethanol experiments may reflect a lower pH at the site of drug acetylation than that observed in the pH experiments after acid addition. With sulfanilamide, which is metabolized by acetylation only in suspensions of isolated rat liver cells (Olsen & Merrland 1981) as substrate, ethanol treatment caused a small but significant increased acetylation; although the medium pH was lower in the ethanol treated cells (table I). With procainamide as substrate, however, ethanol treatment tended to decrease the elimination, while the percentage of acetylated procainamide tended to be enhanced.…”