Inhalation studies on the biotransformation and elimination of [14C] trichlorofluoromethane and [14C] dichlorodifluoromethane in beagles

The possible biotransformation of trichlorofluoromethane (FC-11) and dichlorodifluoromethane (FC-12) was investigated in 4 male and 2 female adult Beagles after a short (6- to 20-min) inhalation. Dogs were anesthetized with ketamine and succinylcholine, intubated, and ventilated artificially. Trichlorofluoromethane (1000–5000 ppm, $\text{v}\text{v}$) or dichlorodifluoromethane 38000–12,000 ppm, $\text{v}\text{v}$) containing up to 180μ Ci of $\text{[}{}^{14}\text{C}\text{]}\text{fluorocarbon}$ was delivered from 110-liter Teflon bags, and all exhalations were collected via a nonrebreathing valve in similar bags for 1 hr. Venous blood samples were withdrawn at appropriate times and assayed for fluorocarbon-associated radioactivity. Exhalation bags were assayed for $\text{[}{}^{14}\text{C}\text{]}\text{fluorocarbon}$ and ¹⁴CO₂. Urine was collected for up to 3 days and assayed for ${}^{14}\text{C}$ metabolites as nonvolatile radioactivity. In some experiments animals were sacrificed 24 hr after exposure and tissues were removed for determination of nonvolatile radioactivity. Essentially all of the administered (inhaled) fluorocarbon was recovered in the exhaled air within 1 hr. Only traces of radioactivity were found in urine or exhaled carbon dioxide. All tissues contained measurable concentrations of nonvolatile radioactivity 24 hr after exposure but together represented less than 1% of the administered dose. It is not possible to determine if these trace levels are associated with metabolites of the fluorocarbons or with the unavoidable radiolabeled impurities present in the administered gas mixture. Neither phenobarbital pretreatment (60 mg/day for 3 days) nor prolonged exposure (50–90 min) produced any alteration of these results. Thus, it can be concluded that FC-11 and FC-12 are relatively refractory to biotransformation after a short inhalation exposure and that they are rapidly exhaled in their unaltered chemical form.     

Mechanisms by which quipazine,a putative serotonin receptor agonist,alters brain 5-hydroxyindole metabolism

Quipazine (2-[1-piperazinyl] quinoline maleate) was shown to increase serotonin and decrease 5-hydroxyindoleacetic acid concentrations in whole brain, several brain regions, and the spinal cord of rats 1 hr after its administration (10 mg/kg, i.p.). In animals with transected spinal cords, quipazine induced stronger activation of extensor reflexes than 5-hydroxytryptophan, chlorimipramine, or Lilly 110140. This response could be blocked by methiothepin. In slices of rat cerebral cortex, quipazine inhibited the uptakes of [³H]-serotonin (EC₅₀ = 10^?6 M) and [³H]-norepinephrine ($\text{EC}{}_{50}\text{= 2 × 10}{}^{\mathrm{?6}}\text{m}$); it was equipotent with Lilly 110140 in inhibiting serotonin uptake, but less potent than chlorimipramine ($\text{EC}{}_{50}\text{= 10}{}^{\mathrm{?7}}\text{m}$). Quipazine administration to rats did not inhibit monoamine oxidase activity, and actually elevated brain tryptophan levels. These observations suggest that the effects of quipazine on brain serotonin and 5-hydroxyindoleacetic acid concentrations could have been caused by direct activation of central serotonin receptors (which would secondarily decrease impulse flow along serotonergic neurones), or by the inhibition of serotonin reuptake, or by both mechanisms.     

Determination of extraction constant,true partition coefficient and formation constant of ion-pair complexes of quaternary ammonium salts,tetrabutylammonium bromide and isopropamide iodide.with some organic anions by a solvent extraction technique

A new method of determining the extraction constant (K_e, the true partition coefficient (TPC) and the formation constant (K_f) of ion-pairs, was developed by the solvent extraction technique. K_e and TPC were estimated from the reciprocals of the intercept and the slope of the regression line obtained by plotting

$\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{APC ? dA}\text{vs}\text{B}\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{dA}\text{APC ? dA}\text{+}\text{A}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{+}\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}$

in the following equation.

$\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{APC ? dA}\text{=}\text{1}\text{K}{}_{\mathrm{e}}\text{+}\text{B}\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{dA}\text{APC ? dA}\text{+}\text{A}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{+}\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{x}\text{1}\text{TPC}$

where [A^T_W] and [B^T_W] are the total concentrations of the cationic compound A and that of the anionic compound B in the aqueous phase respectively, APC is the apparent partition coefficient of A, dA is the partition coefficient of cation A⁺. K_f, which is expressed by K_e/TPC, was then calculated. These constants were determined for the ion-pair extraction of tetrabutylammonium bromide and isopropamide iodide with 4 organic anions, i.e. benzoic acid, p-toluenesulfonic acid, salicylic acid and taurodeoxycholic acid. This new method might be applicable to other ion-pairs without further assumptions except that the molar ratio of the ion-pair formation be 1 : 1.     

The role of lipid,free radical initiator,and oxygen on the kinetics of lipid peroxidation

The relationship between the concentration of unsaturated lipid, free radical initiator, and oxygen concentration on the kinetics of lipid peroxidation was determined. The rate of lipid peroxidation was studied with the thiobarbituric acid (TBA), diene conjugation (DC), and ferrithiocyanate (Fe-SCN) methods. The rate of peroxidation was half-order with respect to unsaturated lipid, initiator, and oxygen. The half-order relationship could be expressed as: $\text{rate}\text{= (}\text{fk}{}_1\text{k}{}_2\text{k}{}_3\text{k}{}_6{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(}\text{azobisisobutyronitrile}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$$\text{(}\text{RH}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(}\text{O}{}_2\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. The half-order relationship was found with linoleic (18:2), linolenic (18:3), and arachidonic (20:4) acids. A linear relationship existed between the logarithm of unsaturation and the rate of peroxidation. No peroxidation of linolenic acid was indicated when the DC method was employed, but was when the TBA and Fe-SCN methods were used.     

Acute tobacco smoke exposure alters the profile of metabolites produced from benzo[a]pyrene by the isolated perfused rabbit lung

The influence of whole tobacco smoke or the gas phase from smoke on the metabolism of $\text{[}{}^{14}\text{C]benzo}\text{[a]}\text{pyrene}$ was e xamined using the isolated perfused rabbit lung model. Fresh whole tobacco smoke mixed with the air ventilating the perfused lung produces an immediate and dose related decrease in the metabolism of $\text{[}{}^{14}\text{C]benzo}\text{[a]}\text{pyrene}$. The metabolites of $\text{[}{}^{14}\text{C]benzo}\text{[a]}\text{pyrene}$, diols, quinones, phenols and polar compounds are generally decreased in quantity. At the lowest level of smoke administered the percentage of BP-7,8-diol produced is increased dramatically. The results indicate that one of the factors contributing to the carcinogenicity of tobacco smoke may be its ability to produce an immediate alteration in the pulmonary metabolism of polycyclic aromatic hydrocarbons.     

Effect of exposure to nitrogen dioxide on t and b cells in mouse spleens

Effects of exposure to nitrogen dioxide (NO₂) on thymus-derived (T) and bursa-derived (B) cells were studied in albino mice. The mice were exposed continuously 24 $\text{h}\text{day}$ to 940 $\text{μg}\text{m}{}^3$ NO₂ and to 188 $\text{μg}\text{m}{}^3$ NO₂ with daily 3-h peaks 5 $\text{days}\text{week}$ of either 470, 940 or 1880 $\text{μg}\text{m}{}^3$ NO₂. After 1, 3, 6, 9 and 12 months of exposure, single-cell suspensions were prepared from spleen and incubated with phytohemagglutinin (PHA) or bacterial lipopolysaccharide (LPS). The PHA and LPS responses from mice exposed to NO₂ were generally depressed when compared with those in mice exposed for the same time periods to filtered air.     

The effects of cadmium, manganese and aluminium on sodium-potassium-activated and magnesium-activated adenosine triphosphatase activity and choline uptake in rat brain synaptosomes

The effects of Cd²⁺, Mn²⁺ and Al³⁺ on rat brain synaptosomal sodium-potassium-activated and magnesium-activated adenosine triphosphatase (Na-K-ATPase and Mg-ATPase) activity and choline uptake were studied. All three types of metal ions inhibited Na-K-ATPase activity more markedly than Mg-ATPase activity. The rank order of inhibition of Na-K-ATPase was: $\text{Cd}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 5.4 μ}\text{M}\text{) >}\text{Mn}{}_{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 955 μ}\text{m}\text{) >}\text{Al}{}^{\mathrm{3+}}\text{(}\text{ic}{}_{50}\text{= 8.3}\text{mM}$). The rank order of inhibition of Mg- was:$\text{Cd}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 316 μ}\text{M}\text{>}\text{Mn}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 5.5}\text{mM}\text{>}\text{Al}{}^{\mathrm{3+}}\text{(}\text{ic}{}_{50}\text{= 21.9}\text{mM}\text{).}\text{Al}{}^{\mathrm{3+}}$ was most potent in inhibiting synaptosomal choline uptake ($\text{ic}{}_{50}\text{= 24μ}\text{M}$ in the absence of Ca²⁺ and 123 μ.M in the presence of 1 mM Ca²⁺). $\text{Cd}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 363 μ}\text{M}\text{)}$ was a more effective inhibitor of choline uptake than $\text{Mn}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 1.2?1.5}\text{mM}\text{)}$ . The presence of 1 mM Ca²⁺ did not alter choline uptake, nor did it antagonize the inhibitory actions of the three metals. Our observations that Cd²⁺ and Al³⁺ inhibited synaptosomal choline uptake, but did not show parallel inhibitory effects on Na-K-ATPase activity directly contradicts the ionic gradient hypothesis. These results are also discussed in relation to the in vivo neurotoxicity of cadmium, manganese and aluminium.     

Effect of α-fluoromethylhistidine,a suicide inhibitor of histidine decarboxylase,on histamine levels in mouse tissues

The effects of α-fluoromethylhistidine (α-FMH), a new suicide inhibitor [Kollonitsch et al., Nature, Lond.274, 906 (1978)], on histidine decarboxylase (HDC) activities and histamine contents of the skin, fundic stomach and brain of mice were investigated. Four hours after i.p. administration of α-FMH to ddy mice, HDC activities in the brain, stomach and skin had decreased in a dose-dependent way (1–25 mg/kg), by a maximum of 90–95%. The histamine levels in the brain and stomach decreased to 50% of the control levels, whereas the level in the skin did not change at all. The time courses of changes in HDC activities and histamine levels were examined. After i.p. administration of 25 mg/kg of α-FMH, HDC activities in these tissues dropped rapidly within 1 hr. Recovery of HDC activities in the stomach and skin began within 12 hr, but the activity in the brain remained low for 24 hr, confirming the result of Garbarg et al. [J. Neurochem.35, 1045 (1980)]. The histamine content of the stomach decreased to 40% of the original level in 8 hr and recovered within 12 hr, whereas that in the brain decreased to 50% and remained low for more than 24 hr. The histamine content of the skin did not change. These results suggest that the histamine level that was not reduced by α-FMH was derived from mast cells. During the above experiments, no behavioral changes of the animals were detected. α-FMH prevented the increase in HDC activity in mouse kidney on day 18 of gestation when administered i.p. every 12 hr from day 13. No abnormalities were seen in fetuses and neonates after this treatment. It is concluded that α-FMH causes depletion of newly synthesized histaminein situ and, thus, is useful for studies on histamine.     

Effect of polychlorinated biphenyls on the immune responses of rhesus monkeys and mice.

The relationship between lipid peroxidation, glutathione (GSH) content, and CCl₄-induced toxicity was investigated in rat hepatocytes isolated by a collagenase-perfusion technique. Two chemical initiators of lipid peroxidation, ferric ions complexed with adenosine diphosphate ($\text{ADP}\text{Fe}{}^{\mathrm{3+}}$) and diethyl maleate, were studied for comparison. CCl₄ caused a reduction of intracellular K⁺ and release of alanine aminotransferase (ALT) into the medium, but no evidence of lipid peroxidation, as measured by the absorbance of thiobarbituric acid (TBA)-reacting materials and lipid-extract diene conjugation. $\text{ADP}\text{Fe}{}^{\mathrm{3+}}$ caused lipid peroxidation, but only a small loss of K⁺. Diethyl maleate caused a greater amount of lipid peroxidation and cell damage than did $\text{ADP}\text{Fe}{}^{\mathrm{3+}}$. Neither response appeared to be related to the GSH content, which was reduced by diethyl maleate, but not by $\text{ADP}\text{Fe}{}^{\mathrm{3+}}$, and by CCl₄ only at the highest dose. The results suggest that lipid peroxidation is not a requisite step in CCl₄-induced toxicity in isolated hepatocytes.     

Influence of dietary polybrominated biphenyl on antibody and host defense responses in mice

Male $\text{Balb}\text{cByJ}$ mice were fed diets containing 5 or 167 ppm of polybrominated biphenyls (PBB) (Firemaster, FFl, lot No. 7042) for either 3 or 6 weeks and then evaluated for their ability to produce antibody and to resist a challenge with malaria or endotoxin. Animals which received a dietary exposure of either 5 or 167 ppm of PBB for 3 or 6 weeks manifested no alteration in their resistance to a challenge infection with Plasmodium berghei (NYU-2), a lethal murine malaria parasite. However, mice which were fed a diet containing 167 ppm of PBB for 3 or 6 weeks had a significant increase in endotoxin (LPS) sensitivity while no change in LPS sensitivity was observed in mice fed 5 ppm of PBB. Peak primary antibody production to sheep erythrocytes, expressed as $\text{PFC}\text{10}{}^{\mathrm{<mtext>6</mtext>}}$ spleen cells, was reduced almost 50% in mice fed a diet containing 167 ppm for 3 weeks, however, no change in $\text{PFC}\text{10}{}^{\mathrm{<mtext>6</mtext>}}$ cells was observed at 6 weeks. A dietary level of 5 ppm of PBB did not alter primary antibody formation at either 3 or 6 weeks. The peak secondary PFC response in both 5- and 167-ppm-treated groups was delayed by 1 day, relative to control values. $\text{PFC}\text{10}{}^{\mathrm{<mtext>6</mtext>}}$ cells, measured on the day of the peak control response, were depressed 60% at 3 weeks and over 85% at 6 weeks at both doses. Serum IgM levels in the mice receiving 167 ppm of PBB were reduced 23–63% during the I° and II° responses, serum IgG was only moderately reduced and serum IgA was unaltered throughout the study. These results suggest that PBB has a minimal effect on antibody production to T-dependent antigens or on host defense to protozoan parasites yet causes a selective depletion of serum immunoglobulin isotypes. The marked increase in LPS sensitivity suggests a compromised macrophage detoxification capability.     

Brain metabolite concentrations and redox states in rats fed diets containing 1,3-butanediol and ethanol

Both ethanol and its dimer 1,3-butanediol (BD) are substrates for alcohol dehydrogenase in liver and thus have many similar effects upon metabolite concentrations and redox states in that organ. Although the mechanism by which ethanol exerts its effects on the brain is not known, it must differ from that in liver since brain contains insignificant amounts of alcohol dehydrogenase. The effects of BD, which does not produce intoxication, and ethanol upon brain were compared in an attempt to determine which changes in metabolite content are related to depression of the CNS. Diets containing 47% of calories as ethanol, BD, or glucose were pair-fed to rats for 62 days. The brains were then removed and frozen with a new apparatus which prevents postmortem changes, and concentrations of metabolites were determined. Substitution of BD for glucose in the diet caused a decrease in the brain content of glucose, lactate and α-oxoglutarate and an increase in glutamate and citrate. Substitution of ethanol for glucose caused only a decrease in the brain content of glucose and an increase in citrate. The ethanol diet, as compared with the BD diet, caused an elevation of the brain content of glucose and a decrease in glutamate. Both BD and ethanol caused a decrease in the free cytoplasmic $\text{[}\text{NADP}{}^{\mathrm{+}}\text{]}\text{[}\text{NADPH}\text{]}$ ratio in brain without changing the $\text{[}\text{NAD}{}^{\mathrm{+}}\text{]}\text{[}\text{NADH}\text{]}$ of cytoplasm or mitochondria.Except for the differences in effect upon glucose and glutamate, BD and ethanol appear to act similarly on the metabolite content of rat brain. It is therefore concluded that the brain is resistant to changes of the measured metabolites during the process of chronic ethanol ingestion. It is further suggested that the small changes observed in the cytoplasmic $\text{[}\text{NADP}{}^{\mathrm{+}}\text{]}\text{[}\text{NADPH}\text{]}$ ratio after ethanol feeding are not related to the depression of CNS activity associated with ethanol ingestion since they also occur after feeding BD.     

Similar activities of nerve growth factor and its homologue proinsulin in intracellular hydrogen peroxide production and metabolism in adipocytes: Transmembrane signalling relative to insulin-mimicking cellular effects

Generation of hydrogen peroxide in adipocyte plasma membrane and its intracellular metabolism and regulatory role have been shown by Mukherjee and co-workers to be a major effector system for insulin [Fedn Proc.35, 1694 (1976); Archs Biochem. Biophys.184, 69 (1977); Biochem. Pharmac.27, 2589 (1978); Fedn Proc.37, 1689 (1978); and Biochem. Pharmac.29, 1239 (1980)]. The possible involvement of this mechanism in the action of structurally similar polypeptides having some insulin-like metabolic effects was investigated. The β-subunit of nerve growth factor (2.5 S NGF, mol. wt 13,500) which has a striking structural homology with proinsulin and has been reported to exert certain insulin-like metabolic effects in its own target tissues (e.g. growing neurites and sympathetic ganglia), and the insulin-derived polypeptides, desalanine-insulin and desoctapeptide-insulin, as well as proinsulin, were examined for their effects on rat adipocytes, employing the technique of formate oxidation. Both NGF and proinsulin caused increased [¹⁴C]formate oxidation, showing similar intrinsic activities, up to a maximum of 140–160% of the basal rate; insulin increased the rate to 190–210% of the basal rate. The relative potencies of the hormones toward H₂O₂ formation and stimulation of the pentose phosphate pathway activity were: insulin $\text{(}\text{EC}{}_{50}\text{: 2.5 × 10}{}^{\mathrm{?11}}\text{M}\text{)}$, desalanine-insulin $\text{(}\text{EC}{}_{50}\text{: 2.5 × 10}{}^{\mathrm{?10}}\text{M}\text{)}$ , proinsulin $\text{(}\text{EC}{}_{50}\text{: 8 × 10}{}^{\mathrm{?9}}\text{M}\text{)}$, and NGF $\text{(}\text{EC}{}_{50}\text{: 10}{}^{\mathrm{?9}}\text{M}\text{)}$. The biologically inactive derivative, desoctapeptide-insulin, did not stimulate glucose oxidation, although it caused a small increase in formate oxidation, with an $\text{EC}{}_{50}\text{of}\text{5 × 10}{}^{\mathrm{?7}}\text{M}$, indicating a suboptimal level of H₂O₂ formation in the elevation of the hexose monophosphate shunt activity. 3-Amino-1,2,4,-triazole (50 mM), which irreversibly decomposes the peroxidatic compound II of the catalase: H₂O₂ complex, inhibited formate oxidation to a greater extent in the hormone-treated cells than in the control cells, whereas sodium azide, an inhibitor of the hemoprotein, catalase, completely inhibited it. The abilities of the polypeptides to stimulate H₂O₂ formation correlated with their abilities to promote lipogenesis from [U-¹⁴C]-D-glucose, as expected of insulin. The cellular GSH/GSSG ratio increased concomitantly with the stimulation of glucose oxidation via the shunt, indicating a tight coupling between these processes. The results confirm that the hydrogen peroxide production is a common basis of the metabolic actions of growth-promoting polypeptide hormones or mitogens beyond their respective receptors.     

Effects of exposure to ozone on susceptibility to experimental tuberculosis

Exposure of mice to 1.96 $\text{mg}\text{m}{}^3$ ozone (O₃) 3 $\text{h}\text{day}$, 5 days/week, for up to 8 weeks beginning at 1 or 2 weeks after challenge with Mycobacterium tuberculosis R 1Rv resulted in significant enhancement of bacterial titers in the lungs at 5 through 8 weeks after challenge when compared to mice exposed to filtered air. Exposure to lower concentrations of O₃ did not produce any significant changes compared to controls.Exposure of guinea pigs to 2.9 $\text{mg}\text{m}{}^3$ O₃ for 3 h immediately after challenge with M. tuberculosis resulted in a suppression of the cutaneous delayed hypersensitivity response, without affecting the serum hemagglutination antibody titers. However, exposure of guinea pigs to 0.98 $\text{mg}\text{m}{}^3$ O³ 3 $\text{h}\text{day}$ for 5 days, initiated within 3 h after the infectious challenge, enhanced hemagglutination antibody titers initially, but the delayed hypersensitivity reaction did not differ from controls.     

Carbon disulphide tetratogenicity and postnatal effects in rat

Pregnant albino rats were exposed to carbon disulphide vapour in concentrations of 50, 100 or 200 $\text{mg}\text{m}{}^3$throughout gestation. Two successive generations (F₁ and F₂) were studied.Concentration levels of 100 and 200 $\text{mg}\text{m}{}^3$ produced marked dose-related impairment in the prenatal development of the F₁ progeny, with increase of early embryonal lethality, reduction in foetal weight and a high incidence of malformations affecting mostly the brain and limbs. Postnatal viability, body weight, lipid and energy metabolism and behaviour were also impaired. Behavioral deviations were observed even at 50 $\text{mg}\text{m}{}^3$.After reaching sexual maturity the F₁ rats were mated within their experimental groups, but no further carbon disulphide exposure was applied. The adverse effects on progeny were still detectable in the F₂ generation. Structural abnormalities of the same type as those found in the F₁ at 100 and 200 $\text{mg}\text{m}{}^3$ exposure were observed in their progeny and, postnatally, statistically significant behavioral changes were observed in the progeny of all test groups.     

Concentrations of nitrate in normal human urine and the effect of nitrate ingestion

A method suitable for the analysis of nitrate in human urine was developed. Normal urinary concentrations of nitrate in urine of human volunteers in Dade County, Florida, where the drinking water contains negligible amounts of nitrate, averaged 47.6 ppm of $\text{NO}{}_3{}^{\mathrm{?}}$ (SD = 17.3). On a vegetable and preserved-meat-free diet, the nitrate concentration was reduced (10 to 30 ppm of $\text{NO}{}_3{}^{\mathrm{?}}$), but, on nitrate-supplemented drinking water, the urinary concentration rose to a range of 34–87 ppm of $\text{NO}{}_3{}^{\mathrm{?}}$. A high vegetable diet resulted in peak urinary nitrate concentrations of 270–425 ppm. These results indicated that nitrate in drinking water is a factor in determining urinary nitrate concentration, but that vegetable ingestion is of greater significance.     

Histamine release by fire ant (Solenopsis) venom.

Venoms from the fire ants Solenopsis invicta and S. geminata were free of detectable histamine but caused histamine release from rat peritoneal mast cells in vitro. On a per ant basis, venom from S. invicta ($\text{ed}{}_{50}\text{= 0·12}\text{venom reservoirs/ml}$) was four times as potent as venom from S. geminata ($\text{ed}{}_{50}\text{= 0·54}\text{venom reservoirs/ml}$). Hexane extracts of venom and a synthetic piperidine were as effective as the venom itself in producing histamine release, indicating that the piperidines in the venom are responsible for most of the activity. Intradermal injection of venom from S. geminata into human subjects produced dose-dependent wheals and subjective responses (itch and/or pain). Ten nanograms of histamine produced effects approximately equivalent to the venom of a single ant and the antihistamine diphenhydramine significantly reduced the wheal and subjective responses to the venom. It was concluded that histamine release plays a major role in the action of fire ant venoms.     

Synthesis and relationship between physicochemical properties and oral absorption of pivaloyloxymethyl esters of parenteral cephalosporins

To obtain fundamental information for designing orally active prodrugs of parenteral cephalosporins, the pivaloyloxymethyl esters of ten parenteral cephalosporins were prepared and their physicochemical properties and oral bioavailability in mice were measured. By esterification, lipophilicity was improved with a decrease in solubility, but all the esters were hydrolyzed to the parent cephalosporins rapidly in homogenates of mouse small intestine. These esters, except cefamandole, showed improved relative bioavailability (BA) when compared with the parent cephalosporins. Quantitative correlation of the partition coefficient (P), hydrolysis rate ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) to the parent cephalosporin and water solubility (S) to the BA of the esters were attempted. A good linear relation between log S and log BA, but no significant relation between log P and log BA or between log $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and log BA was observed. Among the prodrugs, the ester of Cefotiam, ‘1’, which has log P 1.57, and the highest water solubility, 2.71 mg/ml, showed the best BA, 41.8%. The results of this study indicate the importance of water solubility in designing an orally active ester prodrug of the parenteral cephalosporin, if the lipophilicity and hydrolysis rate are sufficiently high.     

Studies on the respiratory uptake and excretion and the skin absorption of methyl n-butyl ketone in humans and dogs

Methyl n-butyl ketone (MnBK) has produced peripheral neuropathy in experimental animals and is implicated in an occupationally produced neuropathy. Since occupational exposure to MnBK is by inhalation or skin contact, both the absorption and elimination of MnBK vapor and its absorption through skin were investigated. Studies were carried out first with male beagle dogs and subsequently with human volunteers. Humans exposed for 7.5 hours to 10 or 50 ppm or for 4 hr to 100 ppm of MnBK vapor absorbed between 75 and 92% of the inhaled vapor. Unchanged MnBK was not eliminated extensively in the postexposure breath or in urine. 2,5-Hexanedione, a metabolite of MnBK known to be neurotoxic in rats, was found in the serum of humans exposed to either 50 or 100 ppm of MnBK. The absorption and elimination of MnBK in dogs was similar to that observed in humans. The skin absorption of [1-¹⁴C]MnBK or a $\text{9}\text{1}$ ($\text{v}\text{v}$) mixture of methyl ethyl ketone $\text{(MEK)}\text{[1-}{}^{14}\text{C]MnBK}$ was determined by excretion analysis. Two volunteers exposed by skin contact to [1-¹⁴C]MnBK absorbed 4.8 μg min^?1 cm^?2 and 8.0 μg min^?1 cm^?2, respectively. Skin exposure to $\text{MEK}\text{[1-}{}^{14}\text{C]MnBK}$ resulted in the respective absorption of 4.2 and 5.6 μg min^?1 cm^?2 by two individuals. Two volunteers given an oral dose of [1-¹⁴C]MnBK (2 μCi; 0.1 mg/kg) excreted 49.9 and 29.0% of the dose, respectively, as respiratory ¹⁴CO₂ within 3 to 5 days and 27.6 and 25.0% of the dose, respectively, in urine within 8 days. Both [1-¹⁴C]MnBK and $\text{MEK}\text{[1-}{}^{14}\text{C]MnBK}$ were absorbed through the skin of dogs. These findings show that MnBK is readily absorbed by the lungs, the gastrointestinal tract, and through the skin, is not eliminated extensively unchanged in breath or urine, and is metabolized to CO₂ and 2,5-hexanedione. Radioactivity derived from [1-¹⁴C]MnBK was excreted slowly by man, suggesting that repeated daily exposure to high concentrations of MnBK may lead to a prolonged exposure to neurotoxic metabolites.     

Adenosine receptor interactions and anxiolytics

$\text{[}{}^3\text{H}\text{]-N}{}^6\text{-}\text{cyclohexyladenosine}$ and [³H]-1,3-diethyl-8-phenylxanthine label the A₁ subtype of adenosine receptor in brain membranes. The affinities of methylxanthines in competing for A₁ adenosine receptors parallel their potencies as locomotor stimulants. The adenosine agonist N⁶-(-phenylisopropyl) adenosine is a potent locomotor depressant. Both diazepam and $\text{N}{}^6\text{-(}\text{l}\text{-}\text{phenylisopropyl}\text{)}\text{adenosine}$ cause locomotor stimulation in a narrow range of subdepressant doses. Combined stimulant doses of the two agents depress motor activity, as do larger doses of either one, given separately.Evidence supporting and against the hypothesis that some of the actions of benzodiazepines are mediated via the adenosine system is reviewed. A number of compounds interact with both systems, probably because of physico-chemical similarities between adenosine and diazepam. It is concluded that of the four classic actions of benzodiazepines, the sedative and muscle relaxant (but not anxiolytic or anticonvulsant) actions could possibly be mediated by adenosine.     

The effect of bencyclane on the oxidative phosphorylation in isolated mitochondria of heart and liver

Our experiments were designed to localize the inhibitory influence of bencyclane² on the process of oxidative phosphorylation in isolated heart and liver mitochondria. The following results were obtained: (1) The state-3-respiration of rat liver and rabbit heart mitochondria was inhibited by bencyclane. This inhibition was dependent on the substrate used as energy donator, being much more pronounced with glutamate $\text{(}\text{ed}{}_{50}\text{= 3.17 × 10}{}^{\mathrm{?8}}\text{or}\text{1.85 × 10}{}^{\mathrm{?7}}\text{moles/mg}$ of protein, respectively) than with succinate $\text{(}\text{ed}{}_{50}\text{= 3.4 × 10}{}^{\mathrm{?7}}\text{or}\text{4.78 × 10}{}^{\mathrm{?7}}\text{moles/mg}$ of protein, respectively). Since the 2,4-dinitrophenol stimulated respiration was equally inhibited, and glutamate transfer through the mitochondrial membrane not influenced, we assume the NADH-coenzyme-Q-reductase to be the site of interaction at the molecular level. (2) Bencyclane stimulates the state-4-respiration of isolated mitochondria with $\text{concentrations}\text{\$}\text{?}\text{= 10}{}^{\mathrm{?5}}\text{M}$. This effect depends on the molar bencyclane concentration of the incubation medium, and is not abolished by the addition of atractyloside, oligomycin or ruthenium red. Therefore, it is suggested that uncoupling of oxidative phosphorylation is the reason for this bencyclane effect. Theoretically, both of the described effects result in a reduction of the amount of ATP in the living cell. Possible consequences on myocardial function and the cardiovascular system are discussed in terms of previously published data in this field.