222 AGRICULTURAL CHEM!CALS

lasting lesion in the central nervous system, but instead mediates its toxic effects by mobiliza- tion from the fat depots of the body.

Those readers who have stayed with us this long will no doubt appreciate the complexity and practical importance of this work. Thus, may we end on a less trying yet valuable note. A gas-liquid chromatographic method has been developed by Brown et aL (cited above) for the detection of I in blood. This technique may well satisfy the needs of industrial medical officers who have to assess and control exposure and may also provide a diagnostic tool in suspected cases of human intoxication. When put to the test in man and experimental dogs, toxic signs and symptoms usually occurred only when a level of 15 pg 1/100 g blood was exceeded. Only occasionally were higher blood levels of I found in the absence of intoxica- tion. Obviously more widespread use of this technique will be required before an assessment can be made of its true potential.

989. Metabolism of diphenamld MeMahon, R. E. & Sullivan, H. R. (1965). The metabolism of the herbicide diphenamid in rats. Biochem. Pharmac. 14, 1085.

Since diphenamid (N,N-dirnethyldiphenylacetamide; I) is now widely used in agriculture as a herbicide on food crops, information concerning its metabolism in vivo is obviously desirable. This is provided by a recent study on rats facilitated by the use of I labelled with carbon-14 (14C).

Following oral, subcutaneous or intraperitoneal administration, I was found to be readily absorbed into the blood stream and relatively easily metabolized to excretable products. The rate of appearance of metabolites in the urine (50 ~o of the administered 14C recovered in 22 hr) also indicates that the rat can metabolize I effectively and that the accumulation of I or its metabolites in the body is unlikely. The main route of metabolism was found to be N-demethylation to nordiphenamid, which was excreted as an N-glucuron- ide. The most interesting metabolite was the O-glucuronide of N-methyl-N-hydroxymethyl diphenylacetamide (II). This finding supports the concept that microsomal N-demethylation proceeds through the intermediate formation of an N-hydroxymethyl intermediate which is usually unstable, but which, in the present case, was stabilized by glueuronide formation. A minor pathway of I metabolism was found to be p-hydroxylation.

990. Hepatotoxicity of ~-naphthylisothiocyanate

Beeker, B. A. & Plaa, G. L. (1965). The nature of a-naphthylisothiocyanate-induced cholestasis. Toxic. appL Pharmac. 7, 680. Becker, B. A. & Plaa, G. L. (1965). Quantitative and temporal delineation of various parameters of liver dysfunction due to ~-naphthylisothioeyanate. Toxic. appl. Pharmac. 7, 708. Zlotnick, A., Horowitz, Ada & Ungar, H. (1965). Alteration in rat liver antigenicity by the administration of alpha-naphthylisothiocyanate. Israel J. med. Sci. 1, 244.

~-Naphthylisothioeyanate (I) has been recommended as an insecticide. Its toxic pro- pensities in man include dermatitis, chills, fever and kidney damage after skin absorption. In addition, long-term administration of I causes bile duct hyperplasia leading to biliary cirrhosis, while acute administration causes bile stasis. Three studies throw more light on liver changes induced by I.

The first of two studies by Becker& Plaa (cited above) is concerned with the nature of cholestasis induced by I, and specifically whether or not it resembles eholestasis produced by obstruction of the bile duet. This was assessed in mice by comparing the effects on liver

AGRICULTURAL CHEMICALS 223

function of a single oral dose of 150 mg I/kg with those induced by ligation of the common bile duct, the tests being made at 2 and 24 hr after treatment. Although both treatments produced equal degrees of hyperbilirubinaemia and sulphobromophthalein (BSP) retention, in other respects cholestasis induced by I was different from extrahe~patie cholestasis. Thus with I, the rate of appearance of hyperbilirubinaemia was more rapid, the increase in plasma bilirubin was exclusively in the conjugated form, and more of the retained BSP was in the metabolized form. This indicates that cholestasis induced by I is intrahepatie in origin.

Alterations in liver activity are investigated more fully in a second study by Becker & Plaa (cited above). As already mentioned, alterations in liver activity, namely elevation of plasma bilirubin and BSP retention, occurred within 2 hr of oral administration of I. T.here was also a prolongation of pentobarbitone-induced loss of the righting reflex. Although this shows that I acts rapidly on the liver, some of these changes persisted as long as 1 month in some animals, hyperbilirubinaemia subsiding first (after about 4 days) and BSP retention last (in 1 animal persisting for 26 days). These findings suggest that I produce mild reversible degenerative changes of the hepatocytes. Since these changes became evident before the proliferation of bile duct epithelium, which does not occur before 24 hr, it appears that I has more than one hepatic site of action. The acute oral LD50 of I was found to be 245 mg/kg.

Finally, I is reported to produce alterations in the production of antigens by the fiver (Zlotnick et aL cited above). This study was prompted by unpublished observations of the authors that I inhibited the hepatocarcinogenic activity of 4-dimethylaminoazobenzene (II), which has been shown to alter the antigenicity of liver tissue prior to carcinogenesis (Baldwin, Br. J. Cancer 1962, 16, 749). Rats were fed diets either unsupplemented or supplemented with II (0.06 ~o), I (0.1 Yo) or a combination of I and II. The antigenicity of the liver cell sap from each group was tested against the specific rabbit antisera. The livers of the rats fed I were found to contain two antigens that were absent from the livers of control animals. One appeared to be identical with that produced by II but the other was specific for I. That this antigen specific for I might be connected with the ability of I to counteract the hepatocarcinogenicity of II is speculation at the moment, but an interesting possibility that deserves future consideration.

991. Dimethoate: A sharp contrast Sanderson, D. M. & Edson, E. F. (1964). Toxicological properties of the organophosphorus insecticide dimethoate. Br. J. ind. Med. 21, 52. Pan'shina, T. N. (1964). Experimental data on the toxicology of the new organophosphoric insecticide phosphamide (rogor, dimethoate). Fedn Proc. Fedn Am. Socs exp. Biol. Transl. Suppl. No. T889. (Translated from Farmak. Toks. 1963, 26, 476).

The organophosphorus pesticide, dimcthoate (I) is no newcomer to these pages. Past memories include the remarkable changes in the toxicity of I when stored in various solvents (Cited in F.C.T. 1963, 1, 289), toxicity to the chick embryo (ibid 1965, 3, 140) and above all the FAO/WHO appraisal of I which led to the allocation of an acceptable daily intake for man of 0--4 pg/kg (ibid 1964, 2, 729).

Two further reports on the toxicology of I reveal a striking contrast in the quality of the work undertaken. The first, a comprehensive and elegant study by Sanderson & Edson (cited above), shows a low acute toxicity to mammals but relatively higher toxicity to avians. Dermal and inhalation toxicity are also very low. Like other organophosphorus pesticides, I acts as a typical cholinesterase inhibitor after oxidation to its active phos- phorothiolate analogue and related metabolites. In two rat feeding studies lasting 6 months