EVALUATION OF SODIUM PYRIDINETHIONE performed on a Tri-Carb 2000, model no. 3003 liquid scintillation spectro- meter (Packard Instrument Co.) under conditions suitable for measuring •5S. The channels ratio method of standardization employing •4C as a secondary counting standard (8) was used to calculate the absolute dis- integration rates for asS. Excretion and metabolism studies Urine and faeces were collected separately from rabbits, the former being collectively summated with urine withdrawn from the bladder at death. A radiometric assay of urine provided information for excretion rate studies, whereas urine subjected to solvent extraction and chromatographic techniques provided the means of establishing the metabolic fate of sodium pyridinethione following dermal administration. One millilitre aliquots of urine were withdrawn from the bladder of rabbits exposed to sodium pyridinethione for 24 h and introduced directly onto a polyethylene column (1.5 x 100 cm) containing Sephadex G10 (Phar- macia Fine Chemicals Co.) and eluted with distilled water. This procedure was repeated for urine acidified to pH 4 with dilute hydrochloric acid and extracted with chloroform. Twenty-six fractions of 5 ml were collected automatically and assayed radiometrically. Fractions containing activity were summated and concentrated by freeze-drying samples of the concen- trated aqueous residue underwent paper chromatography (9) followed by radiochromatographic scanning. The Rf values were calculated. A similar analysis was performed for asS-labelled components in tissue extracts. Tissues were prepared as a protein-free aqueous tiltrate by the Valov method. This flitrate was concentrated by freeze-drying and the concentrated tissue extract applied to the Sephadex column. The radioactive spots were eluted with water and examined in a Unicam SP 800 spectrophotometer. RESULTS AND DISCUSSION Acute toxicity Rabbits received sodium pyridinethione by i.v. infusion 20 mg min -x until a lethal dose was administered as described above. Results are given in Table I.

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table I. Lethal dose of sodium pyridinethione in rabbits with and without assisted respiration Group Mean lethal dose Condition of rabbits size (mg kg -•) Anaesthetized and artificially ventilated 5 Anaesthetized and breathing spontaneously 5 Conscious 5 1608 •230 1041 &196 1159 &228 The mean lethal dose for rabbits with assisted respiration was significantly greater than the other LD values (P= 0.05), i.e. assisted respiration aided the rabbit's tolerance for sodium pyridinethione. Further respiration studies on anaesthetized rabbits breathing spon- taneously (Fig. 2) indicated a 20•o increase in respiration rate during the 'øø I +ve - ve 6O 4O 2d 2O 4O 6O 8O IOC I I I I l 200 400 600 800 1000 1200 Dose (mg kg -I) Figure 2. The mean effects upon respiration, blood pressure and heart rate of infusing sodium pyridinethione intravenously into the marginal ear vein of five anaesthetized rabbits. [•, Respiration rate ¸, heart rate A, blood pressure O, control.