Victor DiStefano

Reduction of Dimethylsulfoxide to Dimethylsulfide in the Cat

A peculiar sweetish odor was noted in the exhaled breath of cats treated with dimethylsulfoxide. By means of gas chromatographic and mass spectrographic techniques, the responsible compound was identified as dimethylsilfid.

Effects of methylmercury on brain biogenic amines in the developing rat pup

Abstract Neonatal rat pups were dosed ip with methylmercury chloride, 5 mg/kg/day, on Days 5, 6, and 7 after birth. Peak brain concentrations of methylmercury were observed 1–3 days after the last injection. The t 1 2 of methylmercury in the brain was 6.6 days. This nonlethal dose produced an initial decrease (on Day 8) in brain 5-HT, 5-HIAA, NE, and DA in the rat pups. Subsequently, the concentrations of these brain constituents increased toward, and then exceeded, control values by Day 15. The initial decreases in the monoamine concentrations were associated with high amounts of methylmercury in the brain, while increased concentrations were seen when the amount of the poison was low. After Day 15 no consistent trends were observed in brain catecholamine concentrations after methylmercury treatment; large deviations from control were noted. Serotonin, on the other hand, continued to rise above control and remained elevated until the end of the experiment (Day 60). This monoamine was further studied with respect to early methylmercury exposure. Methylmercury-treated rat pups displayed decreases in brain tryptophan content, tryptophan hydroxylase activity, and serotonin turnover rate on Day 8 of the experiment. The rat pups matured normally, and no overt signs of the early poisoning were observed.

Observations on the pharmacology and hemolytic activity of dimethyl sulfoxide.

Abstract Single intravenous dosages of 200 mg/kg DMSO to anesthetized cats produced apnea and a transient fall in blood pressure. Subsequent doses of DMSO caused only transient hypotension; apnea was no longer observed. Hemolysis resulting in hemoglobinuria and methemoglobinuria also occurred. The intraperitoneal administration of DMSO or the dilution of DMSO with isotonic saline prior to intravenous administration reduced hemolytic activity.

Urinary metabolites of harmine in the rat and their inhibition of monoamine oxidase

Abstract Tritiated harmine hydrochloride (5 mg/kg, i.p.) was given to male rats daily for 3 days and urine was pooled. Gel filtration on Sephadex G-15 yielded 5 radioactive fractions, I–V. Fraction V was shown to be harmol by comparison with authentic harmol by gel filtration, fluorescence spectrophotometry, paper chromatography, and paper electrophoresis. Fraction IV was shown similarly to be harmine. Pre-injecting rats with 35S-Na2SO3 yielded a radioactive fraction corresponding to III; hydrolysis of III by aryl sulfatase yielded harmol; III was therefore identified as harmol sulfate. Hydrolysis of II by β-glucuronidase yielded harmol and glucuronic acid; II was therefore identified as harmol glucuronide. Fraction I was shown to be a radioactive impurity in the injection solution. The urinary metabolites occurred in the percentages: V–11 per cent, IV-2 per cent, III-69 per cent, II-18 per cent. Rat liver mitochondrial monoamine oxidase activity, measured by the conversion of benzylamine to benzaldehyde, was inhibited 27 per cent at 10−5M, V; 85 percent at 10−6M, IV; 29 per cent at 10−5M, III; and 52 per cent at 10−6M, II.

Mechanism and kinetics of the inhibition of dopamine-β-hydroxylase by 2-mercaptoethylguanidine

Abstract The inhibition of dopamine-β-hydroxylase (DBH) by 2-mercaptoethylguanidine (MEG) was studied using a partially purified DBH preparation. The MEG-induced inhibition of DBH decreased progressively with increasing Cu2+ concentration; equal concentrations of MEG and Cu2+ were without effect, supporting the hypothesis that the mechanism of inhibition is through binding of enzymic Cu. It was shown kinetically that MEG inhibits purified DBH by a two-inhibitor molecule interaction. Since MEG inhibits DBH by binding enzymic Cu, two Cu ions must be available at the active site for binding with the two MEG molecules. Several congeners of MEG and other compounds were used to study the structure-activity relationship (SAR) of the MEG inhibition of DBH. The SAR correlated with a hypothetical model of the enzyme active site based on the information obtained from the kinetic studies of the MEG inhibition of DBH. The structure-activity relationship suggested that the intramolecular distance between the anionic site and the site of β-hydroxylation of the substrate, dopamine (DA), was coincident with the intramolecular distance between the positive charge of the inhibitor and the site of binding of the Cu of DBH.

Behavior and characterization of blood carbon disulfide in rats after inhalation

Abstract Studies were undertaken to characterize free and bound CS2 in the blood of exposed rats. Rats were exposed for 4 hr to CS2 at concentrations of 0.5, 1.0, 2.0, 3.0, or 4.0 mg/liter. Both free and bound or acid-labile CS2 (AL CS2) in the blood increased linearly with inhalation concentration. AL CS2 in the blood also increased linearly with time when rats were exposed to 2 mg/liter of CS2 for up to 4 hr. Free CS2 was eliminated rapidly by a two-exponential, first-order process, with half-times of 8.7 and 55.2 min; AL CS2 was eliminated similarly but more slowly, with half-times of 2.2 and 42.7 hr. The direct proportionality of blood AL CS2 concentrations to the inhalation concentrations and exposure time, coupled with the slow AL CS2 elimination, suggests that blood AL CS2 may be useful as an indicator of total CS2 exposure. When rats were exposed to 4 mg/liter of CS2 for 4 hr, the majority of free and AL CS2 was in the red blood cells. Dialysis studies with whole blood from CS2-exposed rats carried out at 4, 26, and 37°C demonstrated the temperature dependence for the release of free and AL CS2. Plasma and hemolysates of red blood cells from CS2-exposed rats, dialyzed at 4°C, showed no detectable loss of AL CS2 from the plasma and only a slight loss from the hemolysate (10%) after 24 hr. These studies indicate that CS2 binds mainly to macromolecules in blood.

Characterization of carbon disulfide binding in blood and to other biological substances.

Free and bound forms of CS2 are present in subjects exposed to CS2. In rats exposed to 2 mg/liter (approximately 640 ppm) of CS2 for 4 hr, concentrations of acid-labile CS2 (AL CS2, a form of bound CS2 that can be recovered from biological samples by acid treatment) in plasma and red blood cells (RBCs) increased linearly with exposure time. The majority (90%) of the blood AL CS2 was present in the RBCs. About 95% of the AL CS2 in plasma and in RBCs of exposed rats was found in the precipitates after treatment with ammonium sulfate. Incubation of fractionated human RBC lysates with CS2 showed that CS2 binding in these fractions was proportional to the hemoglobin concentration. These observations show that in blood, CS2 binds (in the form of AL CS2) mainly to hemoglobin and to a small extent to other blood proteins. Binding of CS2 to small molecules, including amino acids, accounted for only a small fraction of blood AL CS2. In in vitro studies, CS2 also bound to human albumin, gamma-globulin, and horse heart myoglobin. It was also found that CS2 binds to amino and sulfhydryl compounds at physiological pH. Plasma incubated with CS2 was found to chelate copper. Chelation of copper-containing enzyme by the reaction products of CS2 and biological amines has been observed and has been proposed as one of the mechanisms by which CS2 induces neurotoxicity (M.J. McKenna and V. DiStefano, 1977b, J. Pharmacol. Exp. Ther. 202, 253-266). Radioisotope studies showed that a substantial portion of the radioactivity could not be released from 14CS2-treated plasma and serum upon acid treatment at elevated temperature. These studies suggest the existence of non-acid-labile bound CS2, besides AL CS2, in plasma and serum treated with CS2.

Effect of Growth Velocity on Cardiac Norepinephrine Content in Infant Rats

Summary Cardiac norepinephrine content was determined in rapidly and slowly growing preweaning rats. Between 10 and 20 days of age, when the heart rate normally increases from approximately 400 to 500 beats/min, norepinephrine concentration and heart rate increased simultaneously and the rises of both were greater in rapidly than in slowly growing animals. Rate of growth was directly related to heart rate and norepinephrine content at 15 days of age but not at other times during ontogeny.

Unidimensional chromatographic separation of dansyl catecholamines

Abstract Catecholamines were separated by chromatographing their dansyl derivatives. Unidimensional ascending paper chromatography was used for the separation of DNS-dopamine, DNS-epinephrine, and DNS-norepinephrine. Using the alumina adsorption method, catecholamines were extracted from rat adrenal glands and norepinephrine and epinephrine separated by the dansylation method.

Effects of racemic, (S)- and (R)-methylenedioxyamphetamine on synaptosomal uptake and release of tritiated norepinephrine☆

Abstract Racemic, (S)- and (R)-methylenedioxyamphetamine (MDA) were potent competitive inhibitors of [3H]norepinephrine (NE) uptake by rat hypothalamic synaptosomes. (S)- and (R)-α-methyldopamine were extremely potent competitive inhibitors of [3H]norepinephrine uptake, establishing these compounds as the most potent inhibitors of brain NE uptake reported to date. Racemic. (S)- and (R)-MDA were slightly less potent as releasing agents than (±)-, (+)- and (-)amphetamine respectively. (S)- and (R)-α-methyldopamine were the most potent releasing agents examined.