Metabolism of the carbamate herbicide, asulam, in the rat

Abstract

1. The metabolism of [ring-¹⁴C]asulam, a systemic herbicide highly effective against bracken, has been studied in rats.

2. Most of the radioactivity (76–100% dose) administered orally or intravenously is excreted in the urine in 24 h as unchanged asulam (61–74% dose), N⁴-acetylasulam (8–14%) and N⁴-acetylsulphanilamide (01–2-6%). Small amounts of radioactivity (03–7-4% dose) were present in the faeces, only traces (0–2-0–3%) were excreted in the bile, and no significant ¹⁴CO² was detected.

3. Perfusion of rat liver with ¹⁴C-asulam resulted in more extensive metabolism. Total amounts present in perfusate (81% total), bile (1%) plus liver (14%) were 231% for unchanged asulam, 25·7% for acetylasulam, <1% for acetylsulphanilamide, and 4·5% as conjugates of asulam and acetylasulam, together with several other unidentified metabolites.

4. Asulam is acetylated more readily than sulphanilamide, by rat-liver homogenate, and the highest enzyme activity was associated with the mitochondrial fraction (2·4pmol/mg protein per min).

5. Although not hydroxylated by rats in vivo, evidence was obtained for the hydroxyl-ation of asulam by rat-liver microsomal preparations in vitro.