Effects of clophen A50, 3-methylcholanthrene,pregnenolone-16α-carbonitril and phenobarbital on the hepatic microsomal cytochrome P-450-dependen monooxygenase system in rainbow trout, Salmo gairdneri, of different age and sex

Four groups of rainbow trout (mature male and female, $\text{1}\text{2}\text{-}\text{year-old}$ juvenile, and $\text{1}\text{1}\text{2}\text{-}\text{year-old}$ juvenile) were injected ip at Days 0 and 3 with 20 mg/kg 3-methylcholanthrene (3-MC), 500 mg/kg Clophen A50 (Cl A50), 40 mg/kg pregnenolone-16α-carbonitrile (PCN), respectively, and examined at Day 14. Further, one group of $\text{1}\text{1}\text{2}\text{-}\text{year-old}$ juvenile was injected ip daily with 80 mg/kg phenobarbital (PB) and examined at Day 14. Only 3-MC and Cl A50 markedly elevated the total amount of cytochrome P-450 and the cytochrome P-450-dependent metabolism of paranitroanisole (PNA) and benzo(a)pyrene in the fish liver, whereas no such elevation were observed by PCN or PB. In order to characterize the hepatic cytochrome P-450-dependent metabolism, the Michaelis-Menten kinetic constants of PNA-O-demethylase and the responses of the reactions to α-naphtoflavone, metyrapone, and SKF 525A, in vitro, were studied. These studies (A) showed PCN to significantly elevate apparent K_m of PNA metabolism, whereas no alterations of apparent K_m were seen by 3-MC or Cl A50, (B) indicated the hepatic reactions to be mediated by several species of cytochrome P-450, (C) indicated the formation of alternative form(s) of cytochrome P-450 species in 3-MC- or Cl A50-induced fish when compared to control fish, (D) showed 3-MC- and Cl A50-induced reactions to be similar in character. The presence of differences due to age and sex in the response to the inducers and in the response to the inhibitors, in vitro, is indicated.     

Subcellular distribution of mercury in the rat kidney cortex after exposure to mercuric chloride

The pharmacologic effects and plasma concentrations produced by the ip administration of high doses of thymidine were determined in CDF₁ mice. Within 15 min after the injection of thymidine at a dose of 4.075 g/kg (between LD0 and LD50), mean arterial blood pressure and heart rate fell precipitously and remained depressed for over 6 hr. During the experimental period, sedation and anuresis were also consistently observed in thymidine-treated mice. After a dose of 4.7 g/kg, millimolar plasma thymidine concentrations were maintained for 16 to 20 hr; by contrast, at a lower but nonlethal dose (3.8 g/kg), millimolar plasma thymidine concentrations were maintained for only 9 hr. It is suggested that sustained elevation of circulating thymidine in the range 1–10 mm for periods greater than $\text{1}\text{2}$ day may be associated with toxicity in mice.     

Interactions of chlorpheniramine ethanol combinations: acute toxicity and antihistaminic activity

Significant toxicologic and pharmacologic interactions occurred between chlorpheniramine maleate and 25% $\text{v}\text{v}$ ethanol at several dosage combinations. Conditions of both independence and antagonism of acute toxicity were observed in LD50 determinations of chlorpheniramine-ethanol combinations in mice, and confirmed expected results based on the toxicologic pattern of the agents when administered singly. Enhancement of the antihistaminic action of chlorpheniramine by ethanol was demonstrated during histamine-aerosol challenge studies in guinea pigs.     

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.     

Pulmonary toxicity,hepatic, and extrahepatic metabolism of 2-methylnaphthalene in mice

Male mice ($\text{C57BL}\text{6J}$) were injected once ip with 0.1, 1, 100, 200, 400, 600, 800, or 1000 mg/kg of 2-methylnaphthalene dissolved in corn oil. After 24 hr, the animals were killed and the lungs, livers, and kidneys were prepared for light microscopy. In addition, some lungs were subjected to scanning and transmission electron microscopy. A dose of 200 mg/kg produced a bronchiolar necrosis which affected the nonciliated bronchiolar (Clara) cell; the parenchymal cells remained unaffected. At higher doses of 2-methylnaphthalene (800 mg/kg), in addition to the damaged Clara cell, severe damage to the upper respiratory tract was noted. No liver or kidney pathology was detected by light microscopy in animals treated with the highest dose. No cellular damage was noted in any organ at doses less than 200 mg/kg. Forty-eight hours after a dose of 200–1000 mg/kg of 2-methylnaphthalene, less pulmonary damage was detected by light microscopy. The metabolism of 2-methylnaphthalene was investigated in hepatic, pulmonary, and renal microsomes from $\text{C57BL}\text{6J}$ mice. Lung and liver microsomes produced three isomeric dihydrodiols of 2-methylnaphthalene as well as other monohydroxylated metabolites. Only trace amounts of these metabolites were produced by the kidney.     

Organometal-induced antinociception: A time- and dose-response comparison of triethyl and trimethyl lead and tin

Recent reports have demonstrated that organolead and -tin compounds can alter behavioral reactivity to noxious stimuli. To further define the dose response and temporal characteristics of these neurobehavioral effects, male Fischer 344 rats were injected sc with either one-fourth, one-half, or three-fourths the acute LD50 of triethyl lead (TEL), triethyl tin (TET), trimethyl lead (TML), trimethyl tin (TMT), or distilled water and tested on a 57.5°C hot plate 1, 7, 14, 21, and 28 days after dosing. All four organometals altered hot plate latencies, but the magnitude and time course of these effects differed among the compounds. TEL produced a dose-related increase in latencies which was maximal 1 and 7 days postdosing and had dissipated by 28 days. In contrast, the group administered TML ($\text{3}\text{4}$ LD50) exhibited a late developing antinocioception which became evident 14 days after dosing and persisted throughout the period of testing. The intermediate dose of TMT ($\text{1}\text{2}$ LD50) also produced a delayed increase in response times which was observed 21 and 28 days post-treatment. The $\text{3}\text{4}$ LD50 dose of TMT produced increased hot plate latencies on all post-treatment test days except Day 14. TET ($\text{1}\text{2}$ LD50) produced increased hot plate latencies 1, 7, 14, and 21 days postdosing and also induced a reversible ataxia and akinesia. Higher doses of TET proved lethal to 80% of the animals and lower doses failed to alter response times in the hot plate. These data demonstrate that trialkyl lead and tin compounds can produce time- and dose-related increases in hot plate latencies.     

Metabolic rate of phenacetin and of paracetamol in dogs before and after treatment with phenobarbital or skf 525 A

In six male mongrel dogs the apparent biological half life ($\text{t}\text{2}$) in plasma of intravenously injected phenacetin decreased from 34·6 to 27·2 min after treatment with phenobarbital (25 mg/kg/day for 8 days) (P < 0·025). In the same dogs, the apparent $\text{t}\text{2}$ of intravenously injected phenazone decreased from 78·6 to 32·4 min (P < 0·05). Treatment with SKF 525 A (25 mg/kg) increased the $\text{t}\text{2}$ of phenazone in three other dogs from 70·6 to 246·7 min, whereas the $\text{t}\text{2}$ of phenacetin remained unaffected.The concentration of phenacetin at zero time of intravenous injection increased from 29·5 ± 5·9 S.E. to 43·5 ± 12·6 μg/ml plasma (P < 0·2) after phenobarbital treatment; pretreatment with phenobarbital, however, had no influence on the mean concentration of phenazone at 0 time. SKF 525 A did not influence the zero time concentration of either phenacetin or phenazone.Beagle liver microsomal protein and cytochrome P-450 concentrations increased from 3·2 to 4·2 mg/ml and from 1·0 to 4·1 n-mole/mg protein, respectively, after phenobarbital treatment. Treatment with phenobarbital had no influence on the rates of formation of paracetamol and p-phenetidin nor was the apparent K_m of phenacetin affected.The binding of phenacetin to blood constituents increased from 50 per cent at 5 μg/ml to 59 per cent at 1 μg phenacetin/ml. In the presence of 30 μg phenobarbital/ml blood, the binding of phenacetin at 1 μg/ml blood decreased by 22 per cent.It is concluded that the decrease of the apparent $\text{t}\text{2}$ of phenacetin in dog plasma after phenobarbital treatment may be due to a change in the apparent volume of distribution and/or to some stimulation of an NADPH-dependent enzyme system of the liver less affected by treatment with SKF 525 A than in other species.     

Effects of apomorphine on self-stimulation

In rats, self-stimulation (SS) from posterior lateral hypothalamus and ventromedial tegmentum was suppressed by the ip administration of alpha-methyl-para-tyrosine methyl ester (α-MPT, 100 mg/kg). Apomorphine (0.25 or 0.5 mg/kg) was injected ip $\text{3}\text{1}\text{2}\text{hr}$ after α-MPT treatment. Self-stimulation was reinstated to a significant degree, after 2 hr for the 0.25 mg/kg group, and 3 hr for the 0.5 mg/kg group. Apomorphine given after saline control, elicited an immediate suppression of SS for approximately $\text{1}\text{2}\text{hr}$ in the case of 0.25 mg/kg and $\text{1}\text{1}\text{2}\text{hr}$ for 0.5 mg/kg.     

Comparative toxicity, anticholinesterase action and metabolism of methyl parathion and parathion in sunfish and mice

The in vitro metabolism of methyl parathion (O,O-dimethyl O-p-nitrophenyl phosphorothioate) and parathion (O,O-diethyl O,p-nitrophenyl phosphorothioate) and the sensitivities of the target cholinesterases to inhibition by their oxygen analogs were studied in sunfish (Lepomis gibbosus) and mice to determine the basis for the low toxicity of methyl parathion in sunfish (LD50 > 2500 mg/kg). The LD50 values of parathion and methyl parathion in mice were 13.5 and 11 mg/kg, respectively, and the times to death were much shorter for both compounds in mice than in fish. Low sensitivity of fish cholinesterases to paraoxon as compared to mice accounted for the 10-fold lower toxicity of parathion in fish (LD50, 110 mg/kg). By contrast, sunfish had similar cholinesterase sensitivities to methyl paraoxon and paraoxon. Differences in rates of oxidative formation of the oxygen analog or oxidative cleavage to p-nitrophenol and the corresponding dialkyl thiophosphate could not account for the selective resistance of sunfish to methyl parathion toxicity. Fish and mouse liver homogenates catalyzed a glutathione (GSH)-dependent metabolism of methyl parathion and methyl paraoxon but not of parathion or paraoxon. Additionally, hydrolysis of methyl paraoxon by fish liver homogenates exceeded that for parathion by 5-fold, while methyl paraoxon hydrolysis in mice was $\text{1}\text{2}$ of that of paraoxon. Apparently, a longer time to death in fish provided the opportunity for GSH-dependent and hydrolytic detoxification, which favored methyl parathion and methyl paraoxon relative to parathion and paraoxon. Although in mice the GSH-dependent enzymes also favored detoxification of methyl parathion and methyl paraoxon, this is apparently of less importance because of their high cholinesterase sensitivity and because cleavage and hydrolysis favored parathion and paraoxon.     

The effect of altered hepatic function on the toxicity, plasma disappearance and biliary excretion of diethylstilbestrol

The present investigation was prompted by the observation that the toxicity of diethylstilbestrol (DES) was about 140 times greater in bile duct-ligated (BDL) rats than in control rats when dimethylsulfoxide was the vehicle (24-hr LD50: 0.75 vs 100 mg/kg, respectively). The DES was also more toxic (about 70 times) in the BDL rats when ethyl alcohol was the solvent (0.47 vs 34 mg/kg), and was 5 times more toxic in the BDL rats when administered in propylene glycol (100 vs 530 mg/kg). Since it appeared that altered hepatic function markedly alters the acute toxicity of DES, the plasma disappearance and biliary excretion of DES (0.118 mg/kg, iv) were measured in control rats and in rats with altered hepatic function (produced by surgical removal of two-thirds of the liver, ip injection of 1 ml CCl₄/kg, or bile duct ligation). All three procedures of altering hepatic function decreased the plasma disappearance of DES. In the BDL rats, the total plasma concentration of DES did not decrease over the 2-hr period, suggesting that even when the biliary route of excretion is blocked, other routes are not efficent for the excretion of DES. During the furst 15 min after DES administration, the biliary excretory rate of DES was 2.1 μg/min/kg in control rats and 1.2 μg/min/kg in the rats that had a $\text{2}\text{3}$ hepatectomy or CCl₄. Therefore, impaired hepatic function increased the plasma concentration and toxicity of DES as it decreased its conjugation and biliary excretion.     

Behavioral effects of acrylamide in the mouse

The behavioral toxicity of acrylamide was characterized in the mouse by comparing standard measures of toxicity such as body weight loss and mortality with measures of hindlimb grip strength, locomotor activity, and appetitive behaviors including episodic milk-licking. In the latter test, the mouse received 15-min access daily to a highly palatable, nonessential food substance (10% sweetened milk) that was not available in the maintenance diet. Two strains of mice, CD-1 and $\text{C57BL}\text{6J}$, were injected ip five times weekly with either saline, 20, 60, or 100 mg/kg of acrylamide. Subchronic, but not acute, administration of 100 mg/kg produced weight loss, a severe neuropathy within 3 days, and 100% mortality within 2 weeks. Mice receiving 60 mg/kg subchronically had only a slight loss of body weight but developed a neuropathy within 3 weeks of dosing at which time there was a 50% mortality. Preceding these signs of toxicity, there was a highly significant increase in episodic milk-licking; this increase was significant in both strains of mice by Day 2 and remained elevated throughout the dosing period. The 20 mg/kg dose of acrylamide decreased hindlimb grip strength after 5 weeks of dosing but did not affect milk-licking or body weight even after 7 weeks of dosing. The new use of this test of appetitive behavior has documented a robust effect of acrylamide which preceded other signs of toxicity. The appearance of the various toxic signs was better predicted by the magnitude of the daily dose than the cumulative dose. This study also demonstrated the feasibility of using the mouse in behavioral toxicology.     

Effects of some calcium modulators on monensin toxicity

Monensin is extremely toxic to some domestic animals, like the equine species, if they ingest poultry or cattle rations containing the drug. From a treatment standpoint, no specific compounds are known to alleviate or interact with monensin. Effects of some cardiovascular drugs which antagonize calcium influx in cardioskeletal and smooth muscles were evaluated in mice receiving varying lethal doses (80, 100, 120 or 140 mg/kg ip). Calcium channel blockers (verapamil, diltiazem and lidocaine), a calmodulin antagonist (chlorpromazine), adrenergic receptor blockers (yohimbine, tolazoline and propranolol), and a cardiac glycoside (digoxin) were evaluated for their effects on monensin toxicity following their 30 min pretreatments in mice ip. All the calcium modulators evaluated apart from chlorpromazine, propranolol, and digoxin, potentiated monensin toxicity significantly (p less than 0.05) by decreasing the calculated LD50 of monensin (108 mg/kg); the latter 3 drugs had no effect on monensin toxicity. This study suggests that excess calcium ion influx may not be the only factor responsible for monensin toxicosis in mice.     

Effect of phenobarbital on the distribution and excretion of lead in rats acutely poisoned with lead

Lead (Pb) distribution and excretion after lead injection in rats treated with phenobarbital was examined to investigate the mechanism of the mitigation of Pb toxicity by phenobarbital treatment. Male rats were given 30 $\text{mg}\text{kg}$ of phenobarbital s.c. daily for 5 days, and 24 h later a single i.p. injection of 50 $\text{mg}\text{kg}$ Pb. The amount of Pb in the liver, red blood cells and heart increased markedly after Pb injection in rats treated with phénobarbital, whereas it decreased in lungs and remained unchanged in kidneys. The excretion of Pb via urine and feces was also suppressed by phenobarbital. From these results, it may be concluded that phenobarbital increased accumulation of Pb in the liver, and suppressed the transfer of Pb to other organs.     

Toxicological features of T-2 toxin and related trichothecenes

Toxicological characteristics of T-2 toxin and related trichothecenes, mycotoxins produced by Fusarium, Trichoderma, Verrucaria, and others, were investigated in regard to LD50 values, dermal toxicity, hematological changes, and tumorigenicity. The LD50 values (mg/kg) of T-2 toxin in adult male mice were po 10.5, ip 5.2, sc 2.1, and iv 4.2, and those of nivalenol were ip 4.1 and iv 6.3. These data showed that the lethal toxicity of T-2 toxin and nivalenol was about 10 times higher than deoxynivalenol. Newborn and immature animals were much more susceptible than adults. Inhalation experiments with T-2 toxin revealed that 33 ppb T-2 toxin for 160-min and 140 ppb T-2 toxin for 30-min exposure were enough to cause death in mice within several days. The dermal toxicity of T-2 toxin and macrocyclic trichothecenes (verrucarin A and roridin A) was significantly higher than the other trichothecenes, and the induction of edema and other dermal toxicities is caused by direct attack of the trichothecenes on the capillary vessels. No tumorigenicity of fusarenon-X to dermal tissues was shown in mice. Pretreatments of mice with SH-compounds, prednisolon, phenobarbital, and 3-methylcholanthrene did not change the LD50 value of T-2 toxin.     

Fluorocarbons and general metabolism in the rat, rabbit, and dog.

The metabolic effects of fluorocarbon inhalation were studied in the rat, rabbit, and dog. The fluorocarbons, monofluorotrichloromethane (FC 11) and difluorodichloromethane (FC 12) were inhaled either alone in air or combined in a $\text{50}\text{50}$ or $\text{10}\text{90}$ mixture. In single exposure experiments the only metabolic reactions were produced by FC 11 at 5%, giving a slight hyperglycemia with hyperlactacidemia. In prolonged exposure experiments (inhalation 2 hr/day for 15 days) only FC 11 at 5% produced slight metabolic modifications, these modifications being quickly reversed after inhalation ceased.     

Evidence for multiple forms of receptors for amiloride in transporting epithelia

P.K. GESSNER. Antagonism of the tranylcypromine-meperidine interaction by chlorpromazine in mice, European J. Pharmacol 22 (1973) 187–190.Chlorpromazine protected mice against the toxicity resultant from administration of tranylcypromine and mepertidine 4 hr apart in a $\text{3}\text{10}$ ratio by weight. Doses of 3 mg/kg Chlorpromazine administered i.p. 1 hr prior to meperdine completely reserved the mortality seen after the i.p. administration of 21 mg/kg tranylcypromine and 70 mg/kg meperidine. Chlorpromazine was also found to protect mice significantly against meperidine toxicity.Administration of chlorpromazine, 10 mg/kg, 3 hr after tranylcypromine resulted in a marked fall in body temperature and a failure of meperidine. administered 1 hr later, to bring about the hyperthermic response seen in controls.     

Effects of alterations of metabolism on rubratoxin B toxicity in vivo and in the isolated rat parenchymal cell

The 7-day ip LD50 for rubratoxin B produced by two common soil fungi, Penicillium rubrum and P. purpurogenum, in male mice is 0.27 (0.22–0.34) mg/kg. Pretreatment of mice with the solvent vehicle (either corn oil or saline) had no effect on the LD50. Pretreatment of male mice with pentobarbital increased the LD50 by 29% while SKF 525A pretreatment resulted in a reduction of the LD50 by 71%. Pretreatment with 3-methylcholanthrene (3-MC), however, reduced the LD50 by 43%, suggesting involvement of multiple pathways of metabolism. Treatment with cysteine, a glutathione precursor, increased the LD50 by 132% while pretreatment with diethyl maleate, a glutathione depletor, resulted in a 56% decrease in the rubratoxin B LB50. Treatment of mice with rubratoxin B also caused a dose-related depletion of reduced hepatic glutathione but not total glutathione. Isolated rat parenchymal cells responded to rubratoxin B in a manner similar to that seen in intact animals. Levels of hepatic RNA and protein were decreased while DNA content was unaffected. Cytochrome P-450 content was decreased as was the activity of p-nitroanisole-O-demethylase. Reduced hepatic glutathione was depleted by in vitro incubation with rubratoxin B, while total glutathione was unaffected. Pretreatment of animals with pentobarbital prior to hepatocyte isolation protected against the toxic effect of rubratoxin B. Pretreatment of animals with 3-MC or diethyl maleate, on the other hand, resulted in greater toxicity.     

Nicotyrine inhibits in vivo metabolism of nicotine without increasing its toxicity

The effect of pretreatment with β-nicotyrine on tissue concentrations of nicotine and metabolically formed cotinine was studied in male albino mice injected with [¹⁴C]nicotine. Acute toxicity of nicotine administered ip or iv was also compared in the pretreated and untreated animals. The pretreatment with nicotyrine resulted in a significant dose-dependent increase of nicotine concentrations in the liver, blood, and brain. Concomitantly, there was a significant decrease in the cotinine concentrations suggesting an inhibition of nicotine liver metabolism. Despite the higher concentrations of nicotine in the brain of the pretreated mice, the LD50 after an ip injection of nicotine was not different from the untreated animals. On the other hand there was complete protection against the lethal effect of iv-injected nicotine in the pretreated animals suggesting a direct protective interaction of nicotyrine with nicotine in CNS.     

Tissue distribution,excretion, and metabolism of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the Golden Syrian hamster

The hamster has been reported to be the least sensitive mammalian species to the acute toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The fate of a single dose of [³H]- or [¹⁴C]TCDD (650 μg/kg, ip or po) was assessed in male hamsters for up to 35 days following treatment. The greatest content (percentage dose/g tissue) of radioactivity was found in the liver, adipose tissue, and adrenals. The radioactivity in liver and adipose tissue was identified as unmetabolized TCDD. The rate of ³H or ¹⁴C elimination in urine and feces suggested a first-order process. Similar half-life of elimination ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) values of 12.0 ± 2.0 and 10.8 ± 2.4 days (mean ± SD) were obtianed with ip administered [³H]- and [¹⁴C]TCDD, respectively. With both [³H]- and [¹⁴C]TCDD, approximately 35 and 50% of the radioactivity was eliminated in urine and feces, respectively. The $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for po administered [³H]TCDD was 15.0 ± 2.5 days. High-pressure liquid chromatography of the urine and bile of animals receiving [¹⁴C]TCDD revealed one major and several minor radioactive peaks, none of which corresponded to [¹⁴C]TCDD. The apparent absence of TCDD metabolites in extracts of liver or adipose tissue indicates that the biotransformed products of TCDD are readily excreted in urine and bile. The enhanced rate of metabolism and excretion of TCDD in hamsters relative to other species may in part contribute to, but not totally explain its unusual resistance to TCDD toxicity.     

Inhalation,parenteral and oral LD50 values of Δ9-tetrahydrocannabinol in Fischer rats

In order to resolve the differences in reported LD50 values for Δ⁹-tetrahydrocannabinol (Δ⁹-THC) obtained with various vehicles and rat strains, the oral LD50 values of Δ⁹-THC in a natural vegetable oil vehicle and in an aqueous emulsion were determined in the same rat strain. In addition an iv LD50 value obtained with the emulsion formulation was compared with an inhalation LD50. The natural vegetable oil was pure sesame oil and the aqueous emulsion used orally was comprised of 13% sesame oil, 1% polysorbate 80 and isotonic saline. A similar emulsion (7% sesame oil and 0.5% polysorbate 80) was used to establish the iv and ip LD50 values. The young adult Fischer rat was used in all experiments and the polysorbate 80 concentration in emulsion formulations was maintained below toxic levels for the rodent. Marihuana cuttings were impregnated with Δ⁹-THC and formed into cigarettes which were smoked under controlled conditions of puff volume and duration in an automatic smoking machine to obtain an inhalation LD50. It was demonstrated that behavioral and physiological responses to Δ⁹-THC occurred sooner with the oral emulsion formulation than with the vegetable oil. The intragastric LD50 with the emulsion was 800 mg/kg and with the sesame oil formulation, 1270 mg/kg. The iv LD50 was 36–40 mg/kg, similar to the inhalation dose when the latter was corrected for Δ⁹-THC losses in the rodent nasal passages. The results from this study affirmed that the LD50 values obtained were reliable and that the vehicle did not contribute to the toxicity.