STUDIES ON THE TOXICITY AND PHARMACOLOGIC ACTIONS OF THE DIMETHOXY ESTER OF BENZOTRIAZINE DITHIOPHOSPHORIC ACID (DBD, GUTHION)

¹ Department of Pharmacology, University of Chicago, Chicago 37, Illinois

Measurements of the acute toxicity of the dimethoxy ester of benzotriazine dithiophosphoric acid (DBD) were performed on rats, mice and guinea pigs. When the compound was given intraperitoneally the following approximate LD₅₀ values in mgm./kgm. were obtained: male rats 11.6, female rats 5.7, male mice 5.4, female mice 3.4 and male guinea pigs 40. When DBD was administered orally the approximate LD₅₀ values were 16.4 mgm./kgm. for female rats and80 mgm./kgm. for male guinea pigs.

Measurements of the subacute toxicity of DBD indicated that rats can tolerate relatively high fractions of the acute LD₅₀ dose given repeatedly at daily intervals. Thus no mortality occurred in rats given 0.5 and 1 mgm./kgm./day for 60 days but 80 per cent mortality was observed in a group which received 2 mgm./kgm. of DBD daily by the intraperitoneal route.

The symptoms produced by DBD in all of the species were similar and typical of those caused by cholinergic drugs. Atropine prevented symptoms referable to parasympathetic stimulation and raised the LD₅₀ to about twice the normal value.

Measurements of the anticholinesterase activity of DBD demonstrated that this compound has a weak inhibitory action in vitro since concentrations exceeding 1 x 10^-4 M were necessary to produce 50 per cent inhibition of the enzyme activity of brain, submaxillary gland and serum. However, after intraperitoneal administration of 3.5 mgm./kgm. of DBD to female rats marked inhibition of the enzyme activity of brain and submaxillary gland was noted but the activity of serum was unaffected.

An explanation for the difference between the in vitro and in vivo inhibitory action of DBD on cholinesterase activity was obtained in experiments which demonstrated that the incubation of DBD aerobically with liver slices in Krebs-Ringer phosphate buffer resulted in the production of a metabolite possessing strong anticholinesterase activity. By the use of the cholinesterase test system as an assay procedure for measuring the concentration of active metabolite it was possible to study its rate of formation and properties. The results of this study suggested that the active metabolite of DBD is the oxygen analog in which the sulfur of the thiophosphate linkage is replaced by oxygen.