The Mode of Action of Phenothiazine as an Anthelmintic. The Uptake of 35S-Labelled Phenothiazine by the Tissues of Nematode Parasites and Their Hosts

Abstract

SummaryAscaridia galli, Nippostrongylus muTis, and Haemonchus contortus took up phenothiazine in vitro at the rate of 0.12, 0.18, and 0.26 mg./g. dry wt./hour. The uptake, which was fastest at pH 6.0, was increased in the presence of a wetting agent. It was not proportional to the relative surface area/wet weight of the parasites. The ligaturing of A. galli did not appreciably reduce uptake of the drug in vitro.In vivo, the uptake of phenothiazine by N. muTis and A. galli was about five times as fast as in vitro. In both parasites the drug reached a level of about 1 mg./g. dry wt. 60 minutes after dosing. Thereafter, the phenothiazine content rose steadily to a level of about 1.5-2.5 mg./g. dry wt. which was maintained for several hours. The uptake of the drug by the parasites was 5-10 times greater than that of the mucosa of the small intestine of host animals. The blood, liver, and muscle of host animals also took up the drug in much smaller amounts than did the parasites.When A. galli was exposed to phenothiazine in vitro and in vivo, the concentration of the drug was found in descending order in the tissues of the intestine, the reproductive system, and muscle.The amounts of phenothiazine found in A. galli expelled from the host by the action of the drug varied from 1.6 to 3.3 mg./g. dry wt.; parasites that survived treatment contained 1.1-2.1 mg./g. dry wt. Though the phenothiazine content of N. muTis sometimes rose above 2.5 mg./g. dry wt. this parasite was not obviously affected by the drug. Both A. galli and N. muTis exposed to phenothiazine in vivo retained a large proportion of the drug in their tissues when they were incubated in phenothiazine-free saline in vitro.It is suggested that phenothiazine enters nematode parasites largely through the cuticle. The relatively small uptake of the drug by host animals as compared to their parasites may account for the differential toxicity to host and parasite. The tentative hypothesis is advanced that failure of phenothiazine to "poison" N. muTis may be due to the fact that these parasites are not dependent on energy from anaerobic sources. The necessity for the relatively large doses of phenothiazine needed for anthelmintic treatment is discussed.

The Mode of Action of Phenothiazine As an Anthelmintic II. Phenothiazine in the Intestinal Fluid and Nematode Parasites of Treated Animals

“…Radioactive phenothiazine was synthesized from elemental 35S and purified according to Lazarus and Rogers (1951). Large quantities of the unlabelled drug were purified from the commercial product by the method' of Baker and Brickman (1945).…”

“…DISCUSSION The immediate problem involved in the study of the mode of action of phenothiazine as an anthelmintic is the determination of the form in which the drug is active. Very large doses of the drug are required to obtain efficiency; the drug, though it enters the tissues of Nippostrongylus muris, has no anthelmintic action on this species (Lazarus and Rogers 1951). Further, the efficiency of phenothiazine against a species normally affected by the drug is variable and no satisfactory explanation of this variability has been given.…”

“…Nematodes poisoned with phenothiazine are not unduly affected by it in aerobic environments (Lazarus and Rogers 1951); therefore the biological lesion caused by phenothiazine may be found among the mechanisms by which parasites obtain energy from anaerobic sources.…”

“…at 87°C. Then the parasites were washed repeatedly in saline, dried between filter papers, and prepared for assay of radioactivity by the method of Lazarus and Rogers (1951). The phenothiazine in the intestinal fluid extract was taken up at a slower rate than the phenothiazine in the suspension (Table 2).…”

“…trichloracetic acid. Aliquots of the brei were assayed for total 35S content (Lazarus and Rogers 1951). The remainder was centrifuged at 8,000 r.p.m.…”