Potentiation of CCl4 of hepatotoxicity in rats by a metabolite of 2-butanone: 2,3-butanediol

The role of ketone metabolism in 2-butanone-induced potentiation of carbon tetrachloride (CCl₄) hepatotoxicity was studied in rats. The blood concentrations of 2-butanol, 3-hydroxy-2-butanone and 2,3-butanediol were determined by gas chromatographic analysis after the oral administration of 2-butanone (2.1 ml/kg). The concentrations of 2-butanol, 3-hydroxy-2-butanone and 2,3-butanediol detected 4 h after dosing were 3.2 mg/100 ml, 2.4 mg/100 ml and 8.6 mg/100 ml, respectively. Eighteen hours after 2-butanone, the concentration of 2,3-butanediol rose to 25.6 mg/100 ml, while the concentrations of 2-butanol and 3-hydroxy-2-butanone declined to 0.6 mg/100 ml and 1.4 mg/100 ml, respectively. A 16-h pretreatment with either 2-butanone (2.1 ml/kg, p.o.) or 2,3-butanediol (2.12 ml/kg, p.o.) markedly enhanced the hepototoxic response to CCl₄ (0.1 ml/kg, i.p.), as measured by serum glutamic pyruvic transaminase activity and hepatic triglyceride content. In vivo, limited formation of 3-hydroxy-2-butanone occurred after this dose of 2,3-butanediol. These data suggest that the production of 3-hydroxy-2-butanone and 2,3-butanediol via 2-butanone metabolism may participate in the augmented necrogenic effect of CCl₄ seen after pretreatment with 2-butanone.     

Immunologic sensitization and pulmonary hypersensitivity by repeated inhalation of aromatic isocyanates

The effect of substituents on the relative hepatotoxicity of various derivatives of thiobenzamide (TB) and thiobenzamide-S-oxide (TBSO) has been investigated in the rat. For five para-substituted thiobenzamides (p-XC₆H₄CSNH₂; X = CH₃O, CH₃, H, Cl, CF₃) hepatotoxicity estimated by plasma glutamic pyruvic transaminase (GPT) or plasma bilirubin responses followed a strict Hammett-type dependence on the electronic properties of the substituent, toxicity increasing dramatically with increasing electron donation (? = ?3.4 ?1.4, respectively). This observation is consistent with the possible involvement of a critical S-oxidative biotransformation in the production of hepatic injury by these compounds. p-Hydroxythiobenzamide was not hepatotoxic at the highest dose studied, possibly because routes of biotransformation other than S-oxidation (e.g., conjugation) supervened. 2,6-Disubstituted thiobenzamides bearing either electron-donating or electron-withdrawing substituents also failed to produce hepatic injury. This was suggested to result from the steric effect of the substituents forcing the thioamide group out of conjugation with the aromatic ring. TBSO was significantly more hepatotoxic than TB, as indicated by earlier and/or larger increases in plasma GPT, plasma bilirubin, and hepatic triglycerides. The hepatotoxicity of TBSO was partially blocked by SKF-525A or N-octylimidazole, but was not affected by pretreatment of the rats with phenobarbital. For para-substituted TBSO derivatives (p-XC₆H₄C(SO)NH₂; X = CH₃, H, Cl) the slope of the Hammett correlation for the plasma GPT response was essentially identical to that for the parent TB derivatives. In contrast, the plasma bilirubin response to TBSO was not altered by substituents. The above findings show that the hepatotoxicity of TB derivatives depends strongly on chemical factors in a manner consistent with S-oxidation as a critical step leading to liver injury. However neither the toxic responses to TB nor those to TBSO are uniformly affected in a simple direct manner by induction or inhibition of cytochrome P-450 enzymes. This may indicate that other enzyme systems, oxidative, reductive, or both, may also play a role in governing the toxic responses to TB and TBSO.     

Toxic effects of methylcyclopentadienyl manganese tricarbonyl (MMT) in rats: Role of metabolism

The toxicity of methylcyclopentadienyl manganese tricarbonyl (MMT) has been investigated in relation to its in vivo biotransformation in the rat. The LD₅₀ dose of MMT was found to be 50 mg/kg for oral administration and 23 mg/kg for ip administration. Death appeared to be caused by severe pulmonary hemorrhagic edema. Histological studies of MMT-treated animals revealed pathologic changes in lungs, liver, and kidney. Phenobarbital pretreatment protected rats from the lethal effects of 2.5 times the LD₅₀ dose of MMT, it shifted the site of tissue injury from the lungs to the liver, and it caused a doubling of the rate of biliary excretion of MMT metabolites. The possibility is discussed that MMT per se is toxic without bioactivation, and that the protective effect of phenobarbital pretreatment is due to a first-pass effect preventing toxic concentrations of orally administered MMT from reaching the systemic circulation.     

Release of endogenous catecholamines from isolated rat brain tissue by fenfluramine and N-ethylamphetamine—effects of pargyline

The influence of the monoamine oxidase inhibitor, pargyline. upon the release of endogenous norepinephrine from chopped rat cerebral cortex and endogenous dopamine from chopped rat corpus striatum by fenfluramine and N-ethylamphetamine was examined. Endogenous norepinephrine and dopamine were measured using an enzymatic-isotopic assay. Both fenfluramine and N-ethylamphetamine released significant amounts of each catecholamine. Fenfluramine-induced catecholamine release was associated with the decrease in the total content (i.e. catecholamine in media + catecholamine in tissue) of both cortical norepinephrine and striatal dopamine; N-elhylamphetamine decreased only total striatal dopamine content. In brain tissue obtained from rats pretreated with pargyline HCl (100 mg/kg, 12 hr prior to sacrifice), total cortical norepinephrine content was approximately twice that in the absence of pargyline: striatal dopamine was unchanged. Pargyline pretreatment also resulted in a marked potentiation of the amounts of both catecholamines released by each drug. and in an antagonism of the above drug-induced reductions in catecholamine content. Additionally, after pargyline pretreatment. N-ethylamphetamine reduced total cortical norepinephrine content. When pargyline (2.56 × 10^?1 M) was added to the media containing chopped cortical tissue from unpretreated animals, control content was slightly increased. Only fenfluramine-induced norepinephrine release was potentiated and the degree of potentiation was less than that observed after pargyline pretreatment. As with pargyline in vivo, pargyline in vitro also resulted in an antagonism of the fenfluramine-induced decrease in total norepinephrine and was associated with an N-ethylamphetamine-induced decrease in norepinephrine content. Since the locomotor stimulant effects of both fenfluramine and N-ethylamphetamine are potentiated after pargyline. the data are consistent with the importance of catecholamines to these effects. The data also suggest that pargyline potentiates the behavioral effects of fenfluramine and N-ethylamphetamine in part by increasing the pool of norepinephrine available for release by these drugs and in part by inhibiting the deamination of the released norepinephrine and dopamine by monoamine oxidase. Decreases in total norepinephrine produced by N-ethylamphetamine may reflect alterations in the formation of O-methylated amines.     

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.     

The role of metabolism in N-methylthiobenzamide-induced pneumotoxicity

N-Methylthiobenzamide (NMTB) produces pulmonary edema, hydrothorax, and death in rodents. The objectives of the present studies were to establish a relationship between the lethality of NMTB and its pneumotoxicity and to explore the role of S-oxidation in these events. Pulmonary injury was assessed by measuring [14C]thymidine incorporation into pulmonary DNA. Administration of NMTB resulted in increased pulmonary [14C]thymidine incorporation in both rats and mice. These increases were blocked in both species by pretreatment of animals with sublethal doses of NMTB. However, the lethality of NMTB was not blocked in mice by prior administration of NMTB even though this procedure has been shown to protect rats. 1-Methyl-1-phenyl-3-benzoylthiourea (MPBTU) protected both rats and mice from lethal doses of NMTB and blocked NMTB-induced increases in pulmonary [14C]thymidine incorporation. N-Methylthiobenzamide S-oxide (NMTBSO), a metabolite of NMTB, produced lung injury which was similar to that produced by NMTB. NMTBSO was more potent than NMTB when administered iv, but not when given ip. The role of hepatic metabolism in NMTB pneumotoxicity was examined by administering NMTB to rats which had either undergone partial hepatectomy or been pretreated with N-octylimidazole. Neither of these procedures diminished the lethality of NMTB. These data suggest that NMTB lethality is mediated by pulmonary injury resulting from NMTB S-oxidation in the lung.     

Comparison of the release of [3h]dopamine from isolated corpus striatum by amphetamine,fenfluramine and unlabelled dopamine

Amphetamine-induced release of previously accumulated [³H]dopamine ([³H]DA) was compared to the release of [³H]]DA produced by unlabelled DA and fenfluramine. Like unlabelled DA, amphetamine was more potent than fenfluramine in releasing [³H]DA in all tissue preparations (untreated, pargyline-treated, and pargyline- and reserpine-treated corpus striatal slices). In tissue treated with both reserpine and pargyline, benztropine greatly reduced the efflux of [³H]DA produced by amphetamine and unlabelled DA but had only a slight effect on fenfluramine-induced release of [³H]DA. In the same tissue preparation, Q₁₀ values for the release of [³H]DA produced by 3 × 10^?7 M amphetamine (1.8) and 3 × l0^?6M unlabelled DA (1.7) were similar to that for the spontaneous release of [³H]DA (1.7). However, when the concentrations of amphetamine and unlabelled DA were increased to 10^?4 M, the Q₁₀ values for the release of [³H]DA were diminished at the lower temperatures. These results suggest that amphetamine may release [³H]DA by two mechanisms: (1) by accelerated exchange diffusion due to its use of the DA uptake carrier to enter into neurons (this would predominate at low concentrations of amphetamine), and (2) by passive entrance into neurons and displacement of [³H]Da from binding sites (this would predominate at high concentrations of amphetamine).     

Delayed neurotoxicity of O-ethyl O-4-nitrophenyl phenylphosphonothioate: Subchronic (90 days) oral administration in hens

Delayed neurotoxicity in hens was produced following daily oral administration of 0.1, 0.5, 1.0, 2.5, 5.0, and 10.0 mg/kg of technical (85%) O-ethyl O-4-nitrophenyl phenylphosphonothioate (EPN) in gelatin capsules for 90 days. Daily, three groups of hens were given empty gelatin capsules, 10 mg/kg of tri-o-cresyl phosphate (TOCP), or 1 mg/kg of parathion (O,O-diethyl O-4-nitrophenyl phenylphosphorothioate) and served as gelatin capsule controls, positive controls, and negative controls, respectively. TOCP-Treated hens developed delayed neurotoxicity, and those given parathion showed leg weakness with subsequent recovery when the administration of this agent had stopped. The clinical condition of most ataxic hens deteriorated during the 30-day observation period following the end of the oral administration of EPN. Severity of the clinical condition depended on the size of the daily ingested dose, i.e., while hens given small doses showed only ataxia, those treated with large doses progressed to paralysis and died. Days of administration and “total administered dose” before onset of ataxia depended on the daily dose. Degeneration of myelin and axons in the spinal cord was the most consistent histologic change and was identical to that found in TOCP control hens. Only one hen showed sciatic nerve degeneration. Livers from two hens given the highest dose of EPN manifested a moderate degree of hemosiderosis. Plasma cholin esterase was significantly inhibited in all surviving hens given EPN or TOCP at the end of the observation period. A group of hens treated daily with 0.01 mg/kg of EPN showed no abnormality in gait or behavior, and its plasma cholinesterase activity was not significantly different from that of the control. Hens treated with parathion had plasma cholinesterase activity comparable to that of the control 30 days after the administration of the last dose.     

Desipramine-induced increase in efflux of endogenous dopamine from rat hypothalamus in vitro: Mechanism and specificity

In ritro exposure of minced rat hypothalamus to desipramine (DMI) resulted in a significant elevation of the net efflux of endogenous norepinephrine (NE) and dopamine (DA) at a drug concentration as low as 10 nM. The net efflux of epinephrine was increased only by a 1000-fold greater concentration of desipramine. The increase in efflux of DA was not secondary to changes in the efflux of NE. since nisoxetine elevated the efflux of NE but not of DA and the removal of calcium from the incubation medium blocked the effect of desipramine on the efflux of DA but not of NE. Elimination of calcium did not alter the “spontaneous” hypothalamic efflux of catecholamine. In contrast, desipramine did not affect the net efflux of either DA or NE from the olfactory tubercle or striatum at concentrations of less than 100 μm. At this concentration, the efflux of DA was significantly increased only in the striatum, while the efflux of NE was reduced in the striatum but increased in the olfactory tubercle. Again, in contrast to the hypothalmus, the removal of calcium from the medium markedly reduced “spontaneous” efflux of catecholamine and the desipramine induced efflux of NE. but not the increase in striatal DA efflux produced by desipramine. The results indicate that marked regional differences exist in brain in the ability of desipramine or calcium removal to alter the efflux of both endogenous DA and NE. and suggest that hypothalamic DA and NE neurons are uniquely sensitive to the effects of desipramine.     

Toxicity-distribution relationships among 3-alkylfurans in the mouse lung

The present study was designed to investigate the extent to which a homologous series of 3-alkylfurans, 3-methylfuran, 3-ethylfuran, and 3-pentylfuran, may cause lung injury in mice in order to determine whether the chemical properties of these compounds are related to their toxic potential. The pulmonary concentration and pneumotoxicity of these and various other furan derivatives were also measured to determine if a correlation existed between the magnitude of pneumotoxicity produced by these toxins and their concentration in the lung. Along with the 3-alkylfurans, the other furan derivatives investigated were furan, 2-ethylfuran, 2-furamide, and 3-methylthiophene. The absence or presence of lung damage was evaluated by light microscopy. The quantitative index used to assess and rank the compounds as pneumotoxins was the incorporation of [14C]thymidine into DNA. The results obtained with the 3-alkylfurans showed that 3-methylfuran and 3-ethylfuran were toxic to the lung whereas 3-pentylfuran did not produce pneumotoxicity. 2-Ethylfuran, furan, and 2-furamide also caused lung damage but 3-methylthiophene did not. All the compounds, with the exception of furan, reach the lung in comparable concentrations; therefore, there does not seem to be a correlation between pneumotoxicity and concentration of the toxin in the lung. From these studies, it is also apparent that the pneumotoxicity of the 3-alkylfurans extends beyond the methyl group but that the toxicity decreases with increasing chain length.     

Evidence for carrier-mediated efflux of dopamine from corpus striatum

This study was designed to further evaluate the hypothesis that the efflux of cytoplasmic dopamine from nerve endings of the corpus striatum can occur by carrier-mediated facilitated diffusion. Since dopamine (DA) and sodium ions are thought to be cotransported by the neuronal uptake carrier, the change in DA efflux upon alterations induced in the sodium gradient was observed. Ouabain was used to inhibit Na⁺K⁺-ATPase and thus increase intracellular sodium concentration, while metabolic inhibitors resulted in the same effect by reducing the amount of ATP available for Na⁺K⁺-ATPase. Rats were pretreated with reserpine and incubated with [³H]DA in the presence of pargyline so that the efflux of cytoplasmic [³H]DA could be assessed. Under these conditions, ouabain produced a concentration-related increase in the efflux of [³H]DA from nerve endings of the corpus striatum. The ouabain-induced release of [³H]DA was reduced by 10^?M benztropine, a dopamine uptake inhibitor. Benztropine (10^?5M) also reduced the increase in release of pHjDA when the same tissue preparation was incubated with the metabolic inhibitors sodium cyanide, iodoacetic acid and dinitrophenol. Ouabain at a concentration which caused slight release of [³H]DA potentiated the efflux produced by 3 × 10^?6 M amphetamine, 3 × 10^?6M unlabeled DA and 10^?4M fenfluramine. These results suggest that release of [³H]DA by sympathomimetic amines may be a carrier-mediated process. The Q₁₀ for 10^?4 M ouabain-induced release of [³H]DA was much higher than the Q₁₀ for the above processes and, therefore, the rate-limiting step in ouabain-induced release may involve inactivation of an enzyme such as Na⁺K⁺-ATPase which is coupled to the transport of sodium. Thus, by changing the availability of sodium with ouabain or metabolic inhibitors and by changing the cytoplasmic accessibility of the membrane carrier with benztropine or phenethylamines, the efflux of cytoplasmic [³H]da can be altered markedly.     

Hepatic phase I and phase II biotransformations in quail and trout: comparison to other species commonly used in toxicity testing

The ability of quail and trout to perform a number of representative phase I and phase II biotransformations was examined. To facilitate interspecies comparisons, metabolism of the same substrates was examined simultaneously under uniform conditions for rat, mouse, rabbit, guinea pig, cat, and dog. Both nonmammalian species can metabolize four representative substrates of phase I mixed-function oxidases and one substrate of epoxide hydrolase, though activity tended to be lower than that of the mammals. Important differences in the conjugative pathways were also noted. Among these differences were the quail's relative deficiency in glutathione conjugation and the trout's low ability to conjugate sulfate compounds. Trout liver UDP-glucuronosyltransferase activity was remarkably high toward testosterone and bilirubin, while quail liver formed glucuronides of naphthol, p-nitrophenol, and digitoxigenin-monodigitoxoside. Also noteworthy was the high N-acetyltransferase activity of both quail and trout toward isoniazid, beta-naphthylamine, and 2-aminofluorene. Differences in substrate specificity for a given enzymatic pathway may be an indication that multiple forms of drug metabolizing systems also occur in these nonmammalian species. Observation of several hundred- or even thousand-fold differences between species in their enzyme activities for certain substrates under uniform conditions re-emphasizes the need for caution in extrapolation of xenobiotic metabolism from one species to another.     

Relationship between liver and kidney levels of glutathione and metallothionein in rats

The purpose of this study was to test if the tissue levels of glutathione and metallothioneins were inter-related. In rats, intraperitoneal administration of diethyl maleate or bromobenzene decreased glutathione levels in both the liver and the kidney before doubling the metallothionein concentration in the liver and increasing that in kidneys by 40% starting from 6 h after intraperitoneal administration. Both Zn and Cd produced an increase in hepatic and renal metallothionein levels. However, unlike the responses to diethyl maleate and bromobenzene, the increase in metathionein caused by the metals was not preceded by any significant changes in glutathione levels. Cd decreased the concentration of glutathione in the liver (at 36 h) and kidneys (at 24 h). In contrast, Zn produced an increase and no change in hepatic and renal glutathione concentrations, respectively. The conclusion is that tissue levels of metallothionein and glutathione are not always interrelated.     

Pharmacokinetics of intact cisplatin in plasma. Infusion versus bolus dosing

Plasma levels of total platinum, total filterable platinum and intact cisplatin were monitored in 4 patients who received cisplatin in a regimen consisting of 20 mg/m² by i.v. bolus followed immediately by 80 mg/m² by 6 h infusion. Baseline pharmacokinetic parameters were obtained from a previous study in which 100 mg/m² of cisplatin was administered by a single i.v. bolus. These baseline pharmacokinetic parameters were used in an attempt to predict the pharmacokinetic behavior of cisplatin in the present study. The results demonstrated close agreement between observed and predicted plasma level-time profiles and the area under the plasma concentration-time profiles for cisplatin. The ratios of the various platinum species in plasma over the time course of the study were also consistent with those previously reported. These findings suggest that at a dose of 100 mg/m², the pharmacokinetics of cisplatin and its conversion to other species in plasma are independent of dosage schedule. Since 100 mg/m² is a relatively high dose of cisplatin, it is likely that this approach is applicable to other doses and schedules, and ultimately might prove useful in designing optimum cisplatin dosage regimens.     

Alcohol and local anesthetic effects on Na+-dependent Ca2+ fluxes in brain synaptic membrane vesicles

Resealed synaptic plasma membrane vesicles exhibit Na+-dependent Ca2+ transport activity which may participate in regulation of free Ca2+ concentrations in nerve endings. Sodium chloride-loaded vesicles took up Ca2+ from the external medium (150 mM KCl-25 mM Tris/HCl) in the presence of an outward-directed Na+ gradient, a Ca2+ concentration of 38.6 microM producing half-maximal uptake at 23 degrees. Methanol (5-200 mM) and low concentrations of ethanol (5-25 mM) enhanced the Na+-dependent Ca2+ influx measured at 23 degrees. Higher ethanol concentrations (100-600 mM), as well as 1-propanol and 1-butanol (10-200 mM), produced only inhibition of Ca2+ fluxes. Dixon plot analysis of the inhibitory phase revealed that ethanol inhibited Ca2+ uptake in an apparently competitive manner with respect to Ca2+ concentration, and the Ki obtained from these experiments was 1.01 M ethanol. The inhibition of Ca2+ fluxes by butanol was non-competitive, and the Ki was 68.6 mM. The local anesthetics dibucaine and tetracaine also inhibited Ca2+ fluxes with IC50 values of 1.8 mM for tetracaine and 0.46 mM for dibucaine. The possible physiologic consequences of this inhibition of Na+-Ca2+ countertransport is synaptic membranes by the alcohols and local anesthetics are discussed with regard to neuronal transmission and membrane conductance.     

Potentiation of the hepatotoxicity of carbon tetrachloride following preexposure to chlordecone (kepone) in the male rat.

The effect of carbon tetrachloride (CCl₄) challenge on several parameters of hepatic injury was determined in chlordecone (CD)-pretreated male rats. Following a 15-day feeding of 0 or 10 ppm CD, rats received a single intraperitoneal challenge of 0, 25, 50, 100, or 200 μl CCl₄/kg. Twenty-four hours after CCl₄, biliary excretion of phenolphthalein glucuronide (PG), bile secretion, and serum transaminase (SGPT, SGOT) activities were examined as functional indices of hepatic injury. Feeding of 10 ppm CD alone resulted in decreased biliary excretion of PG (59% of control) but had no effect on bile flow or on serum transaminases. Twenty-four hours after CCl₄ alone, the two high doses caused decreased biliary excretion of PG in the absence of any effect on bile flow and doubled serum transaminases at the highest dose (200 μl/kg). A single challenge of CCl₄ to CD-fed rats resulted in a dose-dependent impairment of PG excretion at a dose of 50 μl/kg and higher. Bile secretory function was severely impaired in the CD-fed animals receiving CCl₄ at the doses of 100 and 200 μl/kg. Decreased bile flow was not seen in any other groups. Greatly potentiated hepatotoxicity was reflected in the form of elevated SGPT and SGOT activities which increased in excess of 30- and 10-fold, respectively, in CD-fed rats challenged with CCl₄ at 100 and 200 μl/kg. Parenchymal liposis (cytoplasmic sudanophilic droplets) developed in all CD-fed rats receiving CCl₄, while necrosis occurred after CCl₄ at 50 μl/kg and increased in a dosedependent manner. CCl₄ controls exhibited parenchymal liposis and limited centrilobular necrosis only at the two highest doses of CCl₄. These data indicate a great potential for production of severe liver damage resulting from interactions of CCl₄ and CD exposure at levels which may be independently nontoxic.     

Stimulation of nonbiliary, intestinal excretion of hexachlorobenzene in rhesus monkeys by mineral oil

Four rhesus monkeys were administered various doses of hexachlorobenzene (HCB) po, to achieve widely varying adipose tissue levels. One month later, each animal was provided with a bile duct bypass allowing for interruption of the enterohepatic circulation (EHC). Effects of mineral oil-supplemented diet and/or interruption of the EHC on urinary, biliary, and fecal excretion of HCB and its metabolites were quantified. Urinary excretion of HCB was not affected by mineral oil but was reduced 20 to 60% by interruption of the EHC. Similarly, biliary excretion of HCB was also reduced 25 to 60% by interruption of the EHC and was not altered by mineral oil. Fecal excretion was increased about fivefold by mineral oil, whereas interruption of the EHC had no effect on the amount of HCB in feces. Results demonstrate that interruption of the EHC reduced urinary and biliary excretion of HCB metabolites, whereas mineral oil specifically stimulated intestinal excretion of the parent compound.     

Complexation in the retention of benzoic acids on a bonded xanthine HPLC stationary phase

The retention of a number of benzoic acids was determined using a bonded xanthine stationary phase (XSP). Retention of benzoate on XSP was studied as a function of pH and organic modifier composition of the mobile phase. The measured retention for 10 substituted benzoic acids was correlated with the complexation constants previously reported for these compounds with theophylline.     

Effect of pH and buffer on the precorneal disposition and ocular penetration of pilocarpine in rabbits

An in vivo technique was utilized to study the effect of pH and buffer capacity on the precorneal disposition and ocular penetration of pilocarpine in the rabbit eye. Tear film pH, tear drug concentration and aqueous humor levels were measured at various times following the instillation of 25 μl of a 1 × 10^?2 M isotonic pilocarpine solution. Test solutions were prepared in 0.0667 M phosphate buffer at various pHs (4.5, 6.0, 7.2) and at various phosphate buffer concentrations (0 M, 0.00667 M, 0.0667 M, 0.1 M) at pH 4.5. It appears that following the instillation of pilocarpine nitrate solutions buffered below the physiological pH of the lacrimal fluid, the extent of depression of the tear film pH and the tear pH re-equilibration time depends not only on the pH of the solution, but also on the precorneal fluid dynamics, and the buffer capacities of the instilled solution and that of the tears. As the buffer capacity of the instilled solution is increased, the ability of incoming tears to raise the pH in the precorneal area to its physiological value is reduced. The increase in the drainage rate due to reflex tear production is an effective mechanism by which the tear film pH re-equilibrates and is also responsible for the large reduction in the drug concentration in the precorneal area. This study examines this mechanism in detail.The depression in the tear film pH can also reduce the ocular penetration of pilocarpine by reducing its corneal permeability. Buffering of the pilocarpine nitrate solution with 0.0667 M phosphate buffer at pH 4.5 causes a two-fold reduction in the aqueous humor level as compared to an unbuffered solution at the same pH. Such a decrease is also predicted based on tear pH-time and tear concentration-time measurements of pilocarpine. This study shows the practical utility of such information in estimating the ocular penetration of drugs. Based on such information it is expected that at least a two-fold reduction in pilocarpine absorption may be caused by reflex tear production. In order to ensure optimum ocular penetration of pilocarpine, the system should not depress the tear film pH appreciably, and should allow rapid tear pH re-equilibration.     

Hexadecane enhances non-biliary,intestinal excretion of stored hexachlorobenzene by rats

[¹⁴C] Hexachlorobenzene (100 mg/kg) was orally administered to 4 groups of rats. Ten days later the effects of hexadecane (3 × 5 ml/kg by gavage) and/or bile duct ligation on urinary and fecal excretion and tissue levels of hexachlorobenzene, were examined. Hexadecane did not affect urinary excretion of hexachlorobenzene, whereas bile duct ligation tripled it. Each of the 3 treatments (n-hexadecane, bile duct ligation and the combination of the two) resulted in a significant increase in fecal excretion of hexachlorobenzene. Moreover, the combination of hexadecane and bile duct ligation produced a greater increase in fecal excretion of hexachlorobenzene in blood, fat and kidney were not affected by any of the treatments, but liver concentrations were reduced significantly by bile duct ligation. Concentrations of hexachlorobenzene in intestinal contents indicate that intestinal-wall passage is the primary route of elimination from the body and that enhancement of elimination occurs mostly distal to the jejunum.