Interactions between THC and cannabidiol in mouse models of cannabinoid activity

Rationale Interest persists in characterizing potential interactions between Δ⁹-tetrahydocannabinol (THC) and other marijuana constituents such as cannabidiol (CBD). Such interactions may have important implications for understanding the long-term health consequences of chronic marijuana use as well as for attempts to develop therapeutic uses for THC and other CB₁ agonists.Objectives We investigated whether CBD may modulate the pharmacological effects of intravenously administered THC or inhaled marijuana smoke on hypoactivity, antinociception, catalepsy, and hypothermia, the well characterized models of cannabinoid activity.Results Intravenously administered CBD possessed very little activity on its own and, at a dose equal to a maximally effective dose of THC (3 mg/kg), failed to alter THC’s effects on any measure. However, higher doses of CBD (ED₅₀=7.4 mg/kg) dose-dependently potentiated the antinociceptive effects of a low dose of THC (0.3 mg/kg). Pretreatment with 30 mg/kg CBD, but not 3 mg/kg, significantly elevated THC blood and brain levels. No interactions between THC and CBD were observed in several variations of a marijuana smoke exposure model. Either quantities of CBD were applied directly to marijuana, CBD and THC were both applied to placebo plant material, or mice were pretreated intravenously with 30 mg/kg CBD before being exposed to marijuana smoke.Conclusions As the amount of CBD found in most marijuana strains in the US is considerably less than that of THC, these results suggest that CBD concentrations relevant to what is normally found in marijuana exert very little, if any, modulatory effects on CB₁-receptor-mediated pharmacological effects of marijuana smoke.     

Measurements of weight and activity in male mice following inhalation of cannabis smoke in a controlled smoke exposure chamber

A smoke exposure device delivering marijuana smoke to mice is described. Standardized smoking conditions were achieved with this unit yielding a concentration of 0.123 mg/liter of delta-9-tetrahydrocannabinol in air. A significant (p < 0.05) decrease in locomotor activity in treated animals was seen following the fourth treatment in a 21-day study where animals were exposed three times weekly for 3 weeks. A significant decrease in body weight for marijuana-exposed animals was also noted. In another study, animals were exposed daily for 7 days. Locomotor activity was significantly decreased in marijuana-exposed animals on Days 6 and 7. There was no significant change in body weight. Following removal from the exposure chamber, the marijuana-exposed animals showed transient hyperactivity (1–3 min) followed by a period of depressed activity lasting 1 hr. Some tolerance to the placebo smoke was seen after the fourth treatment in both studies. Cumulative effects were seen following repeated exposures. These preliminary data suggest that inhalation of marijuana smoke will initiate behavioral changes in mice.     

The pharmacological activity of inhalation exposure to marijuana smoke in mice

Although the majority of cannabinoid users smoke marijuana, the preponderance of laboratory animal research is based on administration of Delta9-tetrahydrocannabinol (Delta9-THC) or other cannabinoid agents via injection. The aim of the present study was to evaluate the impact of inhaling marijuana, or ethanol-extracted placebo smoke in the mouse model of cannabinoid activity by assessing inhibition of spontaneous activity, antinociception, catalepsy, and body temperature. In order to determine dosimetry, blood levels of Delta9-THC were obtained following either marijuana exposure or intravenous injection of Delta(9)-THC. Inhalation exposure to marijuana produced dose-related increases in antinociception and catalepsy, with estimated ED50 doses of Delta9-THC of 2.4 and 3.8 mg/kg, respectively. However, hypothermia and locomotor depression occurred in both the placebo- and marijuana-exposed mice. The CB1 receptor antagonist, SR 141716A antagonized the antinociceptive effects of marijuana (AD50 = 0.6 mg/kg), but only slightly decreased marijuana-induced catalepsy, and failed to alter either the hypothermic or locomotor depressive effects. In contrast, SR 141716A antagonized the antinociceptive, cataleptic, and hypothermic effects of intravenously administered Delta9-THC in mice that were exposed to air alone, though all subjects exhibited locomotor depression, possibly related to the restraint. In accordance with reports of others, these data suggest that exposure to smoke alone has pharmacological consequences. Our findings also indicate that marijuana-induced antinociception is mediated through a CB1-receptor mechanism of action and are consistent with the notion that Delta9-THC is mainly responsible for this effect.     

Cross-tolerance between inhaled Cannabis and intraperitoneal injections of Δ9-THC

Male and female rats were exposed to Cannabis smoke or placebo once every second day for 32 days. Following these 16 trials all animals were injected once intraperitoneally with 4 mg/kg THC. After every third inhalation trial and after the injection the rats were placed on a movement sensor for 3 min. Cannabis smoke significantly reduced activity, relative to baseline scores, during the first 10 inhalation trials but by the thirteenth exposure, tolerance was evident. When the animals were injected with THC, the male rats who had been exposed to Cannabis smoke significantly increased their activity whereas the females did not alter their activity relative to the last inhalation trial. In contrast rats of both sexes that had been exposed to placebo smoke significantly decreased their activity following the injection. This intermodal cross-tolerance is discussed in terms of the role of conditioning in the development of tolerance.     

Chronic marijuana smoke exposure in the rhesus monkey. IV: Neurochemical effects and comparison to acute and chronic exposure to delta-9-tetrahydrocannabinol (THC) in rats.

THC is the major psychoactive constituent of marijuana and is known to produce psychopharmacological effects in humans. These studies were designed to determine whether acute or chronic exposure to marijuana smoke or THC produces in vitro or in vivo neurochemical alterations in rat or monkey brain. For the in vitro study, THC was added (1-100 nM) to membranes prepared from different regions of the rat brain and muscarinic cholinergic (MCh) receptor binding was measured. For the acute in vivo study, rats were injected IP with vehicle, 1, 3, 10, or 30 mg THC/kg and sacrificed 2 h later. For the chronic study, rats were gavaged with vehicle or 10 or 20 mg THC/kg daily, 5 days/week for 90 days and sacrificed either 24 h or 2 months later. Rhesus monkeys were exposed to the smoke of a single 2.6% THC cigarette once a day, 2 or 7 days a week for 1 year. Approximately 7 months after the last exposure, animals were sacrificed by overdose with pentobarbital for neurochemical analyses. In vitro exposure to THC produced a dose-dependent inhibition of MCh receptor binding in several brain areas. This inhibition of MCh receptor binding, however, was also observed with two other nonpsychoactive derivatives of marijuana, cannabidiol and cannabinol. In the rat in vivo study, we found no significant changes in MCh or other neurotransmitter receptor binding in hippocampus, frontal cortex or caudate nucleus after acute or chronic exposure to THC. In the monkey brain, we found no alterations in the concentration of neurotransmitters in caudate nucleus, frontal cortex, hypothalamus or brain stem.(ABSTRACT TRUNCATED AT 250 WORDS)     

Induction of aryl hydrocarbon hydroxylase in rodent lung by cigarette smoke: a potential short-term bioassay.

Aryl hydrocarbon hydroxylase (AHH) activity was increased several fold in the lungs of hamsters, mice and rats after inhalation of cigarette smoke. Hamsters had low basal activity of lung AHH but showed the greatest inducibility (the ratio of induced to noninduced enzyme). Inducibility was lower but the actual levels of enzyme activity, both basal and induced, were higher in mice and highest in rats. Several criteria were met which could qualify the lung AHH assay as a short-term bioassay to aid in the measurement of cigarette toxicity. (1) Within a relatively narrow range, AHH activity increased with the number of cigarettes smoked. (2) In tests with standard reference cigarettes and three commercial brands, cigarettes which delivered high levels of total particulate matter (TPM) in the smoke induced AHH in lung to the highest degree; measures which reduced the TPM, primarily filtering methods, reduced the enzyme-inducing effect. (3) Also, with regard to filtering methods, the type of cigarettes which have been reported to cause the most extensive damage to the respiratory tract of animals in chronic inhalation studies caused the greatest enzyme induction in acute experiments. (4) Assay results can be obtained rapidly; maximum induction occurs within 24 hr after smoke exposure.     

Maternal marijuana smoking alters respiratory timing in the fetal lamb.

The effect of single and repeated maternal marijuana smoke exposure on fetal breathing movements (FBMs) was investigated in 13 fetal lambs in the third trimester. These animals were surgically instrumented for long-term intrauterine recording of diaphragmatic electromyogram (EMG). Maternal inhalation of marijuana smoke [1.84% tetrahydrocannabinol (THC)] increased FBMs and resulted in a more continuous and regular breathing pattern. There was a significant increase in the number of breaths/h (p < 0.01) and the incidence of FBMs (p < 0.001) in the second hour. Breathing activity returned to presmoke level by the third hour. Duration of the longest breathing epoch was significantly increased from 16.8 +/- 3.3 min to 31.9 +/- 5.2 min (p < 0.005). Instantaneous breathing rate was much more stable in the second hour after marijuana exposure (p < 0.01). Inhalation of placebo smoke did not result in any significant change in either overall breathing activity or continuity and stability of the breathing rate. The effects of marijuana smoke on fetal breathing were not observed after repeated smoke exposure. These results suggest that tolerance develops rapidly to the respiratory stimulating effect of marijuana smoke in the fetus.     

Repeated pre-exposure to tobacco smoke potentiates subsequent locomotor responses to nicotine and tobacco smoke but not amphetamine in adult rats

These studies investigated if pre-exposure to tobacco smoke affects the locomotor response to tobacco smoke, nicotine, and amphetamine in adult rats. The rats were habituated to an open field for 3-4 days and then exposed to tobacco smoke for 2 h/day for 13-14 days. The effect of exposure to tobacco smoke on locomotor activity was investigated after 1, 7, and 14 days of smoke exposure and after one 2-hour exposure session that followed a 3-week off period. The effects of tobacco smoke on the locomotor responses to nicotine (0.04 and 0.4 mg/kg, base) and amphetamine (0.1 and 0.5 mg/kg) were investigated on day 14, one day after the last smoke exposure session. The locomotor response to tobacco smoke was increased after 7 and 14 days of smoke exposure and after one exposure session after the 3-week off-period. The acute administration of the high dose of nicotine (0.4 mg/kg) led to a brief period of hypoactivity that was followed by a period of hyperactivity. Pre-exposure to tobacco smoke attenuated the nicotine-induced hypoactivity and potentiated the nicotine-induced hyperactivity. The low dose of nicotine (0.04 mg/kg) did not affect locomotor activity in the control rats but increased the total distance traveled in the tobacco smoke exposed rats. Exposure to tobacco smoke did not affect the locomotor response to amphetamine. These findings indicate that exposure to tobacco smoke leads to tolerance to the depressant effects of nicotine and potentiates the stimulant effects of nicotine and tobacco smoke.     

Spectrophotometric evaluation of carboxyhemoglobin in blood of mice after exposure to marijuana or tobacco smoke in a modified Walton horizontal smoke exposure machine

Carboxyhemoglobin (COHb) values were determined in mice exposed to varying amounts of marijuana and tobacco cigarette smoke utilizing a spectrophotometric technique. Mice were exposed to smoke inhalation in a modified Walton horizontal smoke exposure machine, whereby rodents can be exposed to multiples of 1-min smoke exposure cycles. Smoke exposure was intermittent; during the first 30 sec of each 1-min cycle, the subjects were exposed to smoke diluted either 1:10 or 1:5 with air. During the second half of the cycle the animals were given fresh air. There was a positive linear relationship between COHb values obtained and the number of puffs of marijuana smoke administered via either 2, 4, 6, or 8 "puffs" of marijuana smoke. COHb levels in plasma did not increase in animals given multiple 8-puff episodes of smoke daily as long as a 60-min period was interposed between smoking episodes. COHb values in mice exposed to tobacco smoke were significantly higher than those in mice receiving equal numbers of exposures to marijuana smoke. Mean COHb values of mice receiving 8 consecutive puffs of marijuana smoke were 18.6 and 22.0% saturation, but CO was rapidly cleared from the blood. This rapid clearance suggests that the binding affinity of CO for mouse hemoglobin may be be weaker than that of human hemoglobin. Mice similarly exposed to 6 or 8 puffs of tobacco smoke had mean COHb values of 24.6 and 28.5% saturation, respectively. No acute lethal effects were observed in mice receiving multiple daily episodes of 8 puffs per episode of marijuana smoke, whereas mice exposed to a single 8-puff episode of tobacco smoke suffered about 50% acute lethal effects.     

No increase in carcinogen-DNA adducts in the lungs of monkeys exposed chronically to marijuana smoke.

Rhesus monkeys exposed to marijuana smoke either 7 or 2 days/weeks (HI and LO groups, respectively), or ethanol-extracted marijuana smoke for 7 days/week (EM) or sham treatment (SH) for 1 year were sacrificed 7 months following the last exposure. Pulmonary levels of carcinogen-DNA adducts were determined. Although mean or median adduct levels were not statistically different, 15 of 22 adduct measures were highest in the EM group and lowest 12 of 22 times in the SH group. The levels of aromatic carcinogen-DNA adducts seem no higher in the lungs of animals exposed to marijuana smoke than in untreated animals. Ethanol-extracted marijuana may have effects greater than marijuana itself.     

Responses of rodent hepatic,renal and pulmonary aryl hydrocarbon hydroxylase following exposure to cigarette smoke

Using the British-American Tobacco Co. (B.-A.T.)-Mason inhalation system which releases a precisely-calibrated dilution of tobacco smoke into a chamber, male and female rats, guinea pigs, hamsters and gerbils were exposed to the optimum smoke concentration found to induce rat renal aryl hydrocarbon hydroxylase (AHH) (40 puffs of a 1 : 5 dilution of smoke from cigarettes prepared from a blend of Canadian flue-cured tobaccos). The tissue activity was measured in 9000 g supernatants of homogenates of lung, liver and kidney 6 h following exposure.Cigarette smoke was found to be a potent inducer of AHH, dilutions as high as 1 : 40 inducing this enzyme in rat kidney. Marked tissue, sex and species differences in basal AHH were observed. Induction up to 6-fold, was observed only in lung and kidney of male and female rats. In hamsters and gerbils, lung AHH was induced in both sexes but only renal AHH in female hamsters. In male and female guinea pigs, only the renal AHH was induced some 5-fold. Hepatic AHH was not inducible in any of the species studied. The analysis of changes in AHH activity in a responsive species and tissue(s) could be a valuable technique for the quantitative evaluation of biological effects of low concentrations of cigarette smoke.     

The formation of 3-methylcholanthrene-initiated lung tumors correlates with induction of cytochrome P450IA1 by the carcinogen in fetal but not adult mice

The administration of 3-methylcholanthrene (MC) to pregnant mice results in the formation of lung tumors in the offspring. Previous work has shown that fetuses demonstrating inducibility of aryl hydrocarbon metabolism develop two to five times more lung tumors than induction-nonresponsive littermates. In this study, the effects of fetal versus adult MC exposure were compared with regard to both induction of aryl hydrocarbon hydroxylase activity (AHH) in lung and dependence of lung tumorigenesis on the Ah genotype. In inducible (C57BL/6 X DBA/2)F1 fetal lung supernatants, a single ip injection of 100 mg/kg of MC to the mothers resulted in a maximal 50-fold induction of AHH activity by 8 hr, which persisted for 48 hr. The enzyme data agreed well with RNA blot analysis, as MC caused maximal induction of P450IA1 RNA by 4 hr. For comparison, adult (F1 X DBA/2) mice were given three weekly injections of 100 mg/kg MC and tumor incidences were determined after 16 weeks. No differences were observed between responsive and nonresponsive mice of either sex in the number of mice bearing lung tumors, nor did the tumor multiplicity differ between responsive and nonresponsive males. However, noninducible female mice had a significantly higher tumor multiplicity than their inducible counterparts (p less than 0.025). Single ip injections of MC to adult F1 mice revealed that lung AHH activity was increased only 4- to 7-fold in the adult animal compared to the large fetal induction ratio. The difference in the magnitude of induction was due to the higher constitutive levels of AHH activity seen in adult tissue (4- to 14-fold greater than maximal basal fetal levels), as fetal and adult supernatants showed similar levels of induced activity following MC treatment. These results suggest that the correlation between susceptibility to MC-initiated lung tumors and induction of cytochrome P450IA1 is a unique property of the fetus and may be due, in part, to the low basal levels of fetal activating enzymes and their high induction ratio during the fetal period.     

Effects of single and repeated marijuana smoke exposure on fetal EEG.

The effect of single and repeated marijuana smoke exposure on fetal EEG was investigated in the chronic fetal lamb model using power spectral analysis. Maternal inhalation of marijuana smoke (n = 9) resulted in a significant reduction in total power and power distribution in the delta (1-4 Hz) band, and an increase in power distribution in the faster frequencies in the first h after smoke inhalation. These EEG changes were not observed following maternal inhalation of placebo smoke (n = 5), nor in animals with 3-5 prior exposures to marijuana smoke (n = 5). These results suggest that the effects of marijuana smoke exposure on fetal EEG is short-lived and tolerance develops rapidly with repeated exposure.     

Two hundred and thirteen cases of marijuana toxicoses in dogs

Marijuana (Cannabis sativa) is a commonly used recreational drug among humans; animals may be exposed following ingestion or accidental inhalation of smoke. From January 1998 to January 2002, 213 incidences were recorded of dogs that developed clinical signs following oral exposure to marijuana, with 99% having neurologic signs, and 30% exhibiting gastrointestional signs. The marijuana ingested ranged from 1/2 to 90 g. The lowest dose at which signs occurred was 84.7 mg/kg and the highest reported dose was 26.8 g/kg. Onset of signs ranged from 5 min to 96 h, with most signs occurring within 1 to 3 h after ingestion. The signs lasted from 30 min to 96 h. Management consisted of decontamination, sedation (with diazepam as drug of choice), fluid therapy, thermoregulation and general supportive care. All followed animals made full recoveries.     

Drug-metabolizing enzymes in rat, mouse, pig and human macrophages and the effect of phagocytic activation

Aryl hydrocarbon hydroxylase (AHH) activity mediated by cytochrome P-450 is present in pig hepatic microsomes [10 nmol.3 mg protein-1.hr-1]. AHH activity was detectable in both hepatocytes and Kupffer cells isolated from pig liver biopsy material. These cells were isolated from needle or wedge biopsy material by collagenase perfusion and incubation with collagenase at 37 degrees. The two cell types were separated from the resulting cell suspension as previously described for whole liver. Kupffer cells were enriched by adherence and were cultured for 24 hr prior to harvesting. Cells were harvested, and cell viability was determined. AHH activity was assayed in Kupffer cell and hepatocyte homogenates. Kupffer cell AHH activity was approximately one-eighth the level detected in hepatocytes. To determine whether this enzyme was present in other macrophages, monocytes were isolated from 10 ml of heparinized peripheral blood using Ficoll-Hypaque and were enriched by adherence. After 24 hr in culture, cell viability was assessed and monocytes were identified by by cytochemical staining. AHH activity was detectable in pig monocyte homogenates, and the AHH level was similar to that in pig Kupffer cells. AHH was also easily detectable in human monocytes. This macrophage AHH activity was compared with AHH activity in rat monocytes, mouse Kupffer cells and mouse peritoneal macrophages. Monocyte AHH was relatively stable in cell culture but decreased rapidly upon storage at -70 degrees. Macrophage AHH activity was depressed following phagocytic activation in vitro by latex beads with a concomitant increase in heme oxygenase activity.     

Aryl hydrocarbon hydroxylase induction in rat lung, liver, and male reproductive organs following inhalation exposure to diesel emission

Due to increasing use of diesel-powered vehicles, it has become necessary to assess adverse biological effects of diesel emissions in our environment. The present data describe the effects of inhalation exposure of diesel emission on the specific activities of aryl hydrocarbon hydroxylase (AHH) and epoxide hydrase (EH) in rat lung, liver, testis, and prostate gland. Adult CD strain, Sprague-Dawley male rats (8–10 weeks old) were exposed to diesel emission (1:13 dilution) containing 14.2 ppm ($\text{v}\text{v}$) total hydrocarbon, 20 hr/day for 42 days. Although liver exhibited the greatest overall AHH activity among the organs tested, the percentage increase over control values was highest in the prostate gland. On Day 15 of exposure, AHH activity had increased to 4.5-fold that of the control and remained elevated throughout the entire exposure period. In contrast, AHH induction in liver and lung occurred on Day 33 of exposure, and the maximum AHH induction was observed on Day 42 (1.4- and 1.3-fold increase in lung and liver, respectively). In all the organs tested, EH activity was not changed significantly during the experimental period.     

Passive inhalation of marijuana smoke: urinalysis and room air levels of delta-9-tetrahydrocannabinol

In two separate studies, 5 drug-free male volunteers with a history of marijuana use were passively exposed to the sidestream smoke of 4 and 16 marijuana cigarettes (2.8% delta-9-tetrahydrocannabinol [THC]) for 1 h each day for 6 consecutive days. A third study was similarly performed with 2 marijuana-naive subjects passively exposed to the smoke of 16 marijuana cigarettes. Passive smoke exposure was conducted in a small, unventilated room. Room air levels of THC and CO were monitored frequently. All urine specimens were collected and analyzed by EMIT d.a.u. assay, Abuscreen radioimmunoassay and GC/MS. The studies show that significant amounts of THC were absorbed by all subjects at the higher level of passive smoke exposure (eg., smoke from 16 marijuana cigarettes), resulting in urinary excretion of significant amounts of cannabinoid metabolites. However, it seems improbable that subjects would unknowingly tolerate the noxious smoke conditions produced by this exposure. At the lower level of passive marijuana-smoke exposure, specimens tested positive only infrequently or were negative. Room air levels of THC during passive smoke exposure appeared to be the most critical factor in determining whether a subject produced cannabinoid-positive urine specimens.     

Cerebral and cerebellar neurochemical changes and behavioral manifestations in rats chronically exposed to marijuana smoke.

Groups of male and female Fischer rats were exposed to marijuana cigarette smoke via an automatic smoking machine. Inhaled Δ⁹-tetrahydrocannabinol doses of 0.7, 2, and 4 mg/kg were relevant to man and were given for 12, 18, 27, 57, and 87 days. Another group of rats treated for 87 days was studied after a recovery of 20 days. Control animals inhaled smoke produced by placebo cigarettes. In the first week of exposure, 20% of lower-dosed rats were hyperactive and 50% at the high dose were prostrate or ataxic upon removal from the inhalator. Behavioral aberrations ameliorated within a few hours except for the depression exhibited by males at the high dose. Tolerance to CNS inhibition developed in 1–2 weeks. CNS stimulation, as manifested by hypersensitivity and hyperactivity, progressively involved more animals, primarily females, in all groups during Days 27–57. Tolerance to CNS stimulation developed thereafter. Fighting was displayed by 90% of females and 50% of males at 4 mg/kg by weeks 6–7. Neurotoxicity was expressed by involuntary vertical jumping, predominantly among high-dosed males in weeks 3 and 8. Normal behavior was displayed after cessation of treatment. At necropsy, homogenates of cerebrum and cerebellum were prepared and were analyzed for protein, RNA and acetylcholinesterase (AChE) activity. Cerebral AChE activity in females increased 33–71% after 12 exposures, decreased 10–23% after 57 exposures and rose 12% after 87 exposures. Cerebellar enzyme activity initially increased 15–35% in animals of both sexes during the subchronic phase but declined in females after 27 exposures. The extent of change in enzyme activity was generally reduced with continued treatment. Cerebellar RNA increased approximately 20% in rats of both sexes, but at different time intervals during the subchronic phase, and remained elevated in females at 87 days. Neurochemical changes were sex related and coincided with behavioral manifestations, and some changes extended into the recovery period. Inhalation findings were similar to those obtained earlier by the oral route; however, females demonstrated a greater facility to adapt to the cumulative toxic effects of marijuana smoke.     

Chronic marijuana smoke alters alveolar macrophage morphology and protein expression.

Male rhesus monkeys were subjected to chronic exposure to marijuana smoke. High dose animals (HI) were exposed 7 days/week to 1 MJ cigarette/day; low dose animals (LO) were exposed on 2 consecutive weekend days to 1 MJ cigarette/day; placebo animals (EM) were exposed to 1 ethanol-extracted MJ cigarette/day for 7 days/week; sham animals (SH) were exposed to sham smoking conditions 7 days/week. This regimen was maintained for 1 year and was followed by a 7 month rest period. Alveolar macrophages of animals exposed to the LO and HI dose smoking regimens exhibited irregular cell surface morphology, increased vacuolization, and a spherical conformation upon adherence to plastic. Gel protein profiles of purified macrophages from HI and LO animals showed marked differences in both constitutive and bacterial lipopolysaccharide-elicited protein expression when compared with those of macrophages from the EM or SH animals. These results indicate that chronic THC exposure alters macrophage morphology and protein expression to external stimuli even after a 7 month rest period.     

Induction of monooxygenase activity in the intestine of spot (Leiostomus xanthurus), a marine teleost, by dietary polycyclic aromatic hydrocarbons

The response of intestinal monooxygenases to dietary polycyclic aromatic hydrocarbon (PAH) exposure was evaluated in spot (Leiostomus xanthurus), a marine teleost fish. Ethoxyresorufin O-deethylase (EROD) and aryl hydrocarbon hydroxylase (AHH) activities were highest in the pyloric caeca and in the proximal half of the intestine. Intestinal microsomes from fish given control diets had very low levels of EROD and AHH activities relative to those in liver. After exposure to a diet containing 10 mg of 3-methylcholanthrene/kg of food, the levels of intestinal EROD and AHH activities increased 36-fold and 17-fold, respectively, such that intestinal monooxygenase activity exceeded that of the liver, which was not induced by this treatment. A significant increase in intestinal monooxygenase activity occurred in fish receiving dietary benzo[a]pyrene (BP) at concentrations as low as 10 micrograms of BP/kg food. A 5-fold increase in intestinal AHH and EROD activities was observed within 3 hr after administration of dietary BP. A plateau in gut monooxygenase activity occurred after approximately 3 days of PAH exposure; these activities decreased to control levels within 3 days after replacing the PAH diet with the control diet. Starvation resulted in disappearance of detectable monooxygenase activity. Monoclonal antibody (MAB 1-12-3) against the major PAH-inducible cytochrome P-450 (P-450E) in the liver of the marine teleost (Stenotomus chrysops) [Park et al. Arch. Biochem. Biophys. 249, 399 (1986)] recognized a single protein band in intestinal microsomes, with Mr near 54,000, which we conclude is the spot counterpart to cytochrome P-450E.(ABSTRACT TRUNCATED AT 250 WORDS)