Teratogenic activity of 2-amino-1,3,4-thiadiazole hydrochloride in Wistar rats and the protection afforded by nicotinamide.

Pregnant Wistar rats were each injected once ip with various doses of 2-amino-l,3,4-thiadiazole hydrochloride (ATDA) at days 1-16 of gestation (sperm day = day 0). The optimal teratogenic dose was determined to be 100 mg/kg and this dose was employed throughout the experiment, At autopsy at day 20 resorptions and malformations were found in all litters from treated females. Two periods of increased embryonic susceptibility to the lethal effects of ATDA were observed. The first at day 5 (100% resorbed) and the second at days 9 and 10 (71.5 and 92.5% resorbed). Periods of increased sensitivity to the teratogenic action of ATDA were at days 9 through 13, when the incidence of abnormal fetuses produced exceeded 90%. The major malformations were anophthalmia, microphthalmia, hydrocephalus, short tail, taillessness, ectrodactyly, syndactyly, and cleft palate. Other malformations occurred occasionally. The malformations were related to the developmental stage at the time of treatment. Supplemental treatment with nicotinamide at days 5, 11, 12, and 13 markedly diminished the teratogenic and lethal effects of ATDA, and at day 11 the administration of nicotinamide completely abolished its teratogenic activity. ATDA probably acts by interfering with NAD-dependent enzyme reactions. The first report of teratogenic action for a 2-substituted thiadiazole (fig. 1) was made by Murphy et al. ('57). They injected 2-ethylamino-l,3,4-thiadiazole into rats on gestation day 9, 11, or 12 (sperm day = day 0), but only day-11 treatment produced gross abnormalities, largely confined to the axial skeleton. Little else appears to have been done with respect to the teratogenic action of the 2-substituted thiadiazoles until the reports by Beaudoin ('72) and Scott et al. ('72). The latter demonstrated a depression in DNA synthesis in embryos from females treated with aminothiadiazole. The thiadiazoles have been reported to have carcinostatic activity against mouse tumors (Oleson et al., '55) and a uricogenic effect in man (Krakoff and Magill, '56). Nicotinamide has been used to protect against the antitumor and toxic effect of thiadiazole in mice (Shapiro et al., '57; Humphreys et al., '62) and to protect against the uricogenic effect in human beings (Krakoff and Balis, '59). Recently nicotamide was reported to abolish the teratogenic action of thiadiazole in rats (Beaudoin, '72; Scott et al., '72). TERATOLOGY, 7: 65-72. The present investigation was undertaken to explore the teratogenic action of 2-amin0-1,3,4-thiadiazole over a considerable portion of the gestation period in rats and to investigate the ability of nicotinamide to protect against this action. MATERIALS AND METHODS Virgin female Wistar rats from our colony were used. The animals were maintained on a Rockland Complete Rat Diet ad libitum, with supplemental feedings of lettuce. Day 0 of pregnancy was considered to begin on the morning sperm were found in the vaginal smear. 2-Amino-l,3,4-thiadiazole hydrochloride (ATDA) (Eastman Kodak, Rochester), usually as a 2% aqueous solution, was administered ip, 100 mglkg maternal body weight. In a few experiments various doses were used to determine the optimal teratogenic dose; these will be noted below. Nicotinamide (Sigma) was prepared so that the single dose to be injected was contained in 1 ml of solution. The effect of Received July 24, '72. Accepted Oct. 9, '72. 1 Supported by NIH grant HD00400.