Toxicological evaluation of mu-agonists. Part II: Assessment of toxicity following 30 days of repeated oral dosing of male and female rats with levo-alpha-noracetylmethadol HCl (NorLAAM).

This study evaluated levo-alpha-noracetylmethadol (NorLAAM), the first N-demethylated metabolite of levo-alpha-acetylmethadol (LAAM), a long-acting morphine-like (mu) agonist, approved in 1993 to treat opiate dependence. After acute and 7-day pilot studies to define dose levels appropriate for use in longer term evaluations, Sprague-Dawley rats (20 of each sex per group) were gavaged with doses of 4.4-25.9 mg kg(-1) day(-1) for 30 days followed by a 14-day recovery period. Treatment-related effects included dose-dependent CNS depression paralleled by changes in food consumption, body weight gain and fecal output, as well as reddish urine and abdominal staining. Tolerance developed by day 7. The spectrum of activity observed differed from the parent compound primarily in its time course. Cage-biting and gnawing behavior were observed only with NorLAAM. Mortality was dose-dependent, with deaths occurring predominantly during the first week. At day 30, all male-treated groups exhibited statistically significant, dose-dependent decreases in body weight gain and increases in serum cholesterol that returned to the control range following recovery. Increases in brain/body weight and testes/body weight ratios and decreases in kidney/brain, liver/brain, spleen/brain and heart/brain ratios, as well as decreases in kidney, liver, spleen and heart absolute weights, achieved statistical significance only for males. At terminal sacrifice, histological findings in the kidneys included increased incidences of tubular mineral deposition in mid- and high-dose groups of both sexes and of corticomedullary mineral deposition in females. Hepatic centrilobular hypertrophy was evident in male and female mid- and high-dose groups. Histopathological changes abated following the recovery period. In summary, acute and repeated administration of NorLAAM produced a pharmacodynamic profile commensurate with its role as the primary N-demethylated metabolite of LAAM, which is more potent and less lipophilic than the parent compound; this was reflected in the toxicological outcomes observed. Like LAAM, NorLAAM's overall pattern of activity is consistent with its activity as a mu-agonist, which stimulates hepatic microsomal enzymes in rodents.

Toxicological evaluation of mu-agonists. Part I: Assessment of toxicity following 30 days of repeated oral dosing of male and female rats with levo-alpha-acetylmethadol HCl (LAAM).

This study evaluated levo-alpha-acetylmethadol hydrochloride (LAAM), a long-acting morphine-like (mu) agonist approved in 1993 to treat opiate dependence. Sprague-Dawley rate (20/sex/group) were gavaged with doses of 3.0-33.5 mg kg-1 for 30 days followed by a 14-day drug-free recovery period. Treatment-related effects included dose-dependent CNS depression, decreased food consumption and body weight gain, reddish urine and abdominal staining. Tolerance developed by day 7. Mortality was dose-dependent; deaths occurred predominantly during the first week. Increased alanine aminotransferase (SGOT, AST) and lactate dehydrogenase (LDH), observed only in high-dose males, were associated with findings in liver. Decreases in spleen/brain weight and increases in brain/body weight ratios were seen in both sexes. Decreases in weights of heart, liver and kidney achieved statistical significance only for high-dose groups. Kidneys of mid- and high-dose groups displayed intertubular mineral/crystal deposition, focal corticomedullary mineralization and focal regenerative tubular epithelium. Centrilobular hypertrophy was observed in livers of high-dose males and mid- and high-dose females. Following the recovery period, decreased body weights and increased brain/body weight ratios occurred in mid-dose males and low-dose females. Weights of liver and kidney and organ/brain weight ratios were decreased in mid-dose males. Histopathological findings observed in kidneys and livers had abated. In summary, acute and repeated administration of LAAM produced a spectrum of activity consistent with its profile as a long-acting pure mu-agonist which stimulates microsomal enzymes in rodents. Renal and hepatic effects seen in initially drug-naive rats treated with morphine-type agonists are not observed in tolerant individuals stabilized on mu-agonists to treat opiate dependence.

Dominant lethal assay of chlordecone and its distribution in the male reproductive tissues of the rat.

Male rats received 3.6 or 11.4 mg/kg/day of chlordecone orally for 5 days. Some statistically significant events were seen in the reproductive data of females mated to males receiving chlordecone. However, these events did not follow a consistent pattern and do not suggest the conclusion that chlordecone causes dominant lethal effects. Male rats received a single oral dose (40 mg/kg) of chlordecone and were killed at 1, 2, 3, 5, 7, 14 or 21 days. Chlordecone was distributed throughout the reproductive tract. The descending order of concentration was seminal vesicular fluid greater than prostate greater than vas deferens greater than seminal vesicle greater than unwashed sperm greater than washed sperm. It is concluded that chlordecone is well distributed throughout the reproductive tract of the male rat, appears in the ejaculate, and does not appear to produce dominant lethal effects.

Pharmacological effects of 1,2,3,5,6,10b-hexahydropyrido[2,3g]indolizine, a bridged-nicotine analog.

The racemate of a bridged-nicotine (BN) analog was synthesized and resolved into its enantiomers for pharmacological comparisons to (+)- and (-)-nicotine. The EC50 values for (-)- and (+)-nicotine and (-)- and (+)-BN were 4, 170, 53 and 400 microM, respectively, for producing contractions of guinea-pig ilea. (-)-Nicotine was an effective antinociceptive agent in the mouse tail-flick procedure at i.v. doses of 0.1-0.3 mg/kg, whereas the isomers of BN failed to alter tail-flick response in doses up to 5 mg/kg. (-)-Nicotine (0.01-0.3 mg/kg, i.v.) increased blood pressure and decreased heart rate in anesthetized rats. Neither (+)- nor (-)-BN altered blood pressure and heart rate in rats in this dosage range. At doses of 3-100 mg/kg, (+)-BN produced an increase in blood pressure without changing heart rate, while (-)-BN decreased both blood pressure and heart rate. Bridging the pyrrolidine and pyridine rings decreased biologic activity and did not result in stereoselectivity greater than that observed with (+)- and (-)-nicotine. It appears that there may be subpopulations of nicotine receptors to which the isomers of BN do not interact.

Acute toxicity of monochlorophenols, dichlorophenols and pentachlorophenol in the mouse.

Acute oral LD50 values were determined for 2-, 3-, and 4-chlorophenol, 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5 dichlorophenol and pentachlorophenol in male and female mice. LD50 values (mg/kg) ranged from 117 (females) and 177 (males) for pentachlorophenol to 2389 (females) and 2643 (males) for 3,5-dichlorophenol. It was found that 2-chlorophenol and 3-chlorophenol were considerably more toxic than the dichlorophenol series. Values for males and females were generally similar, the major differences being with pentachlorophenol and 2,5-dichlorophenol, where in both cases the female LD50 was lower.

Acute and subchronic toxicity of 2,4-dichlorophenol in CD-1 mice.

The acute oral LD50 of 2,4-dichlorophenol (2,4-DCP) employing corn oil as vehicle was determined to be 1352 mg/kg for female and 1276 mg/kg for male CD-1 mice. CD-1 mice of both sexes were exposed to 2,4-DCP in drinking water containing 10% Emulphor for 90 days at concentrations of 0.2, 0.6, and 2.0 mg/ml providing theoretical daily doses of 50, 150, and 500 mg/kg. These concentrations resulted in mean daily doses of 50, 143, and 491 mg/kg for females and 40, 114, and 383 mg/kg for males. In both sexes, fluid consumption was lower in the vehicle control group (10% Emulphor) and in the 2,4-DCP treated groups than in the naive controls (deionized water). There were no biologically significant differences in body weight gain between females or males in the vehicle control and experimental groups. No differences were found in terminal organ weights or organ weight ratios in either sex. Hematological differences were observed in males only and included an increase in leukocytes (high dose) and an increase in polymorphonuclears (low dose). Clinical chemistry parameters were altered in females only and included a decrease in creatinine (low dose), an increase in BUN/creatinine ratio (mid dose), and an increase in ALP (high dose). In an assessment of the hepatic microsomal mixed function oxidase system, no significant differences were found in the components of the system, component activity, the kinetics of ethylmorphine N-demethylase, or the metabolism of testosterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Reproductive toxicity and lack of dominant lethal effects of 2,4-dinitrotoluene in the male rat.

Adult male Sprague Dawley rats were gavaged with 2,4-dinitrotoluene (2,4-DNT) dissolved in corn oil at 0, 60, 180, or 240 mg/kg/day for five days. A single oral dose (0.5 mg/kg) of triethylenemelamine was used as a positive control. Induction of dominant lethal events was scored on the basis of early fetal deaths. At the two lower doses, no consistent changes were observed in the numbers of pre-implantation losses, implantation sites, or living or non-living fetuses. The highest dose of 2,4-DNT tested resulted in a marked decrease in the numbers of sperm-positive females (determined by microscopic examination of vaginal smears for sperm) and pregnant females. These two effects diminished in the latter weeks of mating. The low number of pregnant females at the highest dose made meaningful statistical evaluations difficult. The results indicate that 2,4-DNT does not cause dominant lethal mutations but does adversely affect reproductive performance.

The effects of acetaldehyde and acrolein on blood pressure in guanethidine-pretreated hypertensive rats.

These experiments were undertaken to study the effect of the interaction of the antihypertensive agent guanethidine and two aldehydes possessing sympathomimetic activity on the blood pressure of spontaneously hypertensive rats (SHR). Acetaldehyde, when administered iv to acutely guanethidine-pretreated (15 mg/kg) SHRs under urethane anesthesia, caused a potentiated pressor response in the dose range of 3 to 40 mg/kg. When administered iv to chronically guanethidine-pretreated SHRs, a pressor response was noted at low doses and a depressor response at high doses. Acrolein (0.05 to 0.5 mg/kg) produced a pressor response at low doses and a depressor response at high doses in both acutely and chronically guanethidine-pretreated SHRs. Pressor responses, particularly to acetaldehyde, may be due to an enlarged tyramine-releasable pool, hyperreactivity of alpha adrenergic receptors of SHRs, or guanethidine inhibition of norepinephrine reuptake. Depressor responses to high doses of aldehydes may be attributed to vagal stimulation or direct vasodilation. It is concluded that there is a significant interaction between the aldehydes and guanethidine which may have implications for someone undergoing treatment with guanethidine for hypertension while being exposed to acetaldehyde and related compounds from ethanol and tobacco smoke.

Effects of intravenous acetaldehyde, acrolein, formaldehyde and propionaldehyde on arterial blood pressure following acute guanethidine treatment.

Guanethidine (G) is currently used in the treatment of essential hypertension. Acetaldehyde (A), acrolein (AR), formaldehyde (F) and propionaldehyde (P) are constituents of cigarette smoke and (A) is also an intermediate oxidative metabolite of ethanol. These aldehydes are known to produce sympathomimetic effects by the release of NE from adrenergic neurons and to exert cardioinhibitory effects. The type of predominant effect is dose-dependent. This study was undertaken to determine if these aldehydes result in sympathomimetic effects in the presence of G (15 mg/kg iv) in anesthetized rats. G enhanced the pressor responses to A and P in dose ranges of 5-20 and 5-10 mg/kg respectively. However, AR and F at dose ranges of 0.05-5 and 0.1-10 mg/kg, respectively, elicited only depressor responses after G. Thus, A and P exerted greater sympathomimetic effects through the release of intraneuronal NE in the presence of G. The adrenergic neuronal blocking action of G changes the blood pressure effects of AR and F. When these two compounds are administered in the absence of G, they cause predominant pressor effects, whereas in the presence of G a depressor response is noted. This depressor response is possibly by vagal stimulation and/or direct vasodilation.

Adrenergic receptors in the nucleus tractus solitarii of the rat.

The nucleus tractus solitarii (NTS) is an area of the medulla in which baroreceptor afferent fibers mediating an inhibition of vasoconstriction terminate. The NTS also appears to be a site at which alpha-adrenergic receptors may be involved in blood pressure control. alpha- and beta-adrenergic agonists and antagonists were injected into the NTS via stainless steel cannulae and the effects on blood pressure determined. Norepinephrine (NE) and isoproterenol (ISO) caused dose-related decreases in mean arterial blood pressure (MABP). Phentolamine (PH) and propranolol (PR) caused dose-related increases in MABP. PH pretreatment in the NTS blocked the effects of ISO, but not NE. The effect of increased baroreceptor impulses to the NTS, produced by altering perfusion of the carotid sinus was blocked by propranolol. These results indicate the presence of beta- as well as alpha-receptors in the NTS, and also suggest the existence of presynaptic beta-receptors which facilitate neurotransmission.

Mesoionic xanthine analogues: phosphodiesterase inhibitory and hypotensive activity.

Several mesoionic thiazolo[3,2-alphapyrimidines and mesoionic 1,3,4-thiadiazol[3,2-alpha-pyrimidines were evaluated as inhibitors of cyclic-AMP phosphodiesterase. While small alkyl substituents at the 6 position have no significant effect on activity, phenyl and benzyl substituents enhance activity. Mesoionic structures such as 1 (R2 = H; R8 = Et) possess 20 to 40 times the activity of theophylline when the R6 substituent is phenyl or 4-chlorobenzyl. methyl and ethyl substitution at the 2 position essentially abolishes activity. Although plagued by solubility problems, several of the mesoionic derivatives were found to display weak hypotensive effects in vivo.

Retention of inhaled 2-methylfuran and 2,5-dimethylfuran.

The respiratory tract retention of 2-methylfuran and 2,5-dimethylfuran in the dog have been studied as part of a broad investigation of substances found in the vapor phase of cigarette smoke. Retention of 2-methylfuran tended to be higher that that of 2,5-dimethylfuran in the upper, lower and total respiratory tract. Uptake of 2-methylfuran ranged from 63-88% in these regions while it was only 53-62% for 2,5-dimethylfuran. Retention of 2,5-dimethylfuran was lower than any of the other compounds studied. However, the majority of either compound will be absorbed by the respiratory tract when inhalation occurs.

Excretion of chlordecone by the gastrointestinal tract: evidence for a nonbiliary mechanism.

Workers exposed to chlordecone (Kepone), a toxic organochlorine pesticide, excreted larger amounts of chlordecone in bile than in stool, suggesting that it may undergo enterohepatic recirculation. We found in a single subject that equal amounts of chlordecone and of its reduced metabolite, chlordecone alcohol, were excreted in bile at a rate four times as great as in stool. When biliary contents were diverted from the intestine through a T tube, fecal excretion of chlordecone alcohol was abolished, presumably due to interruption of its passage via bile to intestine. This change was not accompanied by disappearance of chlordecone from the stool. The amount of chlordecone in stool when bile was diverted was increased six- to tenfold over that when diverted bile was continuously infused into the duodenum. Analogous experiments with [14C]-chlordecone-treated rats in which bile flow was exteriorized through a plastic cannula showed that the excretion of radioactivity in feces was in the same range when bile was reinfused in the duodenum or was totally diverted. Moreover, in rats with bile diverted, cholestyramine, an anion-exchange resin which binds chlordecone in vitro, doubled the excretion of radioactivity in stool. A similar effect was observed in intact animals. We conclude that chlordecone enters the intestinal lumen from a nonbiliary source, probably the gut, and that net excretion of chlordecone from this source can be augmented by cholestyramine.

Respiratory retention and acute toxicity of furan.

The respiratory tract retention of furan has been studied in dogs as part of a broad investigation of compounds found in the vapor phase of cigarette smoke. The LD50 of furan has also been determined in mice and rats and the LC50 in mice. Respiratory uptake of furan was between 90 and 95%, varying inversely with the ventilatory rate. Retention was not affected by tidal volume changes but was directly related to concentration inhaled. Intraperitoneal LD50 values were 5.2 mg/kg for rats and 7.0 mg/kg for mice. The LC50 for mice was 0.12 microgram/mL. These results indicate the high toxicity of furan and that it is readily absorbed by the inhalation route.

Cholestyramine: use as a new therapeutic approach for chlordecone (kepone) poisoning.

In rats, as reported in humans, chlordecone (Kepone) is excreted predominantly in the feces. Cholestyramine, an anion exchange resin, binds chlordecone in rat intestine, increases its excretion into the feces, and decreases its content in the tissues. The resin appears to offer a practical method for treating chronic poisoning with this and possibly with other lipophilic toxins.