Personality factors in human drug self-administration

By comparing MMPI profiles of sedative-dependent subjects during pentobarbital self-administration with comparable subjects during drug abstinence, the present study has found that self-administration tends to increase rather than decrease indicators of personal distress (MMPI scale scores). This finding agrees fully with other studies of drug effects on mood of drug-dependent subjects. (This finding should disturb only those who equate reinforcement with euphoria and other pleasurable states. Those familiar with the concept of reinforcement understand that reinforcement deals only with behavior and implies nothing about corresponding subjective states). Only scores on the Hypomania scale of the MMPI were found to correlate significantly with amount of daily drug intake, and this relationship occurred primarily in females. Scores on the Depression scale were correlated significantly with the daily pattern of drug-taking behavior. However, in neither case is it known whether the relationship reflects influences of personality factors on drug-taking behavior, or influences of drug-taking behavior on the obtained personality measures. Other research will be needed to answer this question. Clinically depressed individuals may constitute a special sub-group of subjects in which scores on many MMPI scales are related to daily amount of drug intake. Studies of human drug self-administration provide an excellent opportunity for more detailed research into these and other clinical research questions.

Biphasic effect of doxapram on hypnotic activity of pentobarbital in mice

The effect of doxapram, a respiratory stimulant, on the pentobarbital sleeping time was investigated in mice. The sleeping time induced by the intraperitoneal injection of pentobarbital was prolonged 0--120 min after the administration of doxapram (25-100 mg/kg, i.p.). The pretreatment with doxapram 60 min before had no effect on the anesthetic time induced by ether and on the sleeping time induced by the intracerebroventricular injection of pentobarbital, while increased the lethality of pentobarbital only slightly and the levels of pentobarbital in the plasma and brain significantly. The activities of pentobarbital oxidase and aminopyrine N-demethylase in the 9000 X g supernatant fraction of the liver were inhibited by the pretreatment with doxapram 60 min before the test. On the other hand, 12-24 hr after the injection of doxapram the pentobarbital sleeping time was markedly shortened. Thus, the biphasic effect of doxapram, prolongation at first and shortening later, on the pentobarbital sleeping time was observed. It is possible that doxapram inhibits the hepatic microsomal drug-metabolizing enzymes without an increase in the sensitivity of the central nervous system at first and stimulates these enzymes during the second phase.

Weak-acid transport in the small intestine: discrimination in the lamina propria

Studies on the intestinal transport of weak acids suggest that the subepithelial tissues exhibit a modest, but significant, ability to discriminate between the ionized and nonionized forms. This suggestion has been tested directly in experiments using an in vitro preparation of rat small intestine from which the epithelial cells were removed, but in which the structural and functional integrity of the subepithelial tissues was maintained. Studies on the effects of potential difference on the fluxes of weak acids in this preparation showed that the ratio of permeabilities for the ionized and nonionized species (Pi/Pni) was indeed less than one, and of a magnitude comparable to the value suggested by analysis of transport in the intact tissue. (Pi/Pni) for the subepithelial tissue decreased as pH was increased, and the discriminatory properties of the tissue were abolished [(Pi/Pni)=1] on treatment with the cationic macromolecule polyethyleneimine (PEI). These observations suggested that the discriminatory properties of the subepithelial tissues were determined by fixed anionic sites, and morphological studies with PEI indicated that such sites were concentrated in the region of the basement membrane.

The role of hepatic microsomal enzymes in the modulation of phencyclidine-induced toxicity

The LD50 of phencyclidine (PCP, 234 mumol/kg, i.p.) in male Swiss mice decreased by 62% in animals pretreated with 2-diethylamino-2,2-diphenylvalerate hydrochloride (SKF-525A, 40 mg/kg), and increased by 74% and 20% in animals pretreated with sodium phenobarbital (75 mg/kg), and 3-methylcholanthrene (70 mg/kg), respectively, No Significant change in the LD50 was observed with cysteine or diethylmaleate pretreatment. The treatment with PCP at 179 mumol/kg/day i.p. for 7 days resulted in body weight decrement in the first 2 days and gradual increment thereafter. The increase was only 33% of the control group. The food intake was also lower in the PCP treated group of animals. PCP withdrawal led to an increase in food intake as well as body weight at a normal rate. The ratio of liver weight to body weight was not significantly higher than that of control during the treatment period. The administration of PCP for 7 days did not alter the activities of liver function enzyme markers. However, within 12 h of the initial PCP treatment a 85% increase in activity of serum glutamicoxalacetic transaminase was observed. Later the enzyme activity reached close to normal levels. No liver lesions at the light microscopic level were observed. Treatment of mice for 4 days with PCP (179 mumol/kg) caused no significant change in pentobarbital sleeping time.

Alterations in pentobarbital and meperidine pharmacokinetics induced by bile duct ligation in the rat

Although impaired microsomal drug metabolism has been demonstrated in response to bile duct ligation, there has been little previous assessment of the effects of extrahepatic biliary obstruction on drug pharmacokinetics in vivo. In this study, the effects of bile duct ligation on overall disposition on pentobarbital and meperidine in the rat have been assessed in vivo and in isolated perfused rat livers. A significant reduction in clearance of both compounds was seen in response to bile duct ligation. No change in protein binding of either drug was demonstrated, but alterations in initial volume of distribution of both drugs occurred in response to extrahepatic biliary tract obstruction. A significant reduction in the rate of perfusate flow was also seen in perfused liver experiments using livers from animals with previous bile duct ligation. Reduction in clearance of both a high extraction drug (meperidine) and a lower extraction drug (pentobrbital) in response to bile duct ligation suggests that both hepatic blood flow and drug metabolizing enzyme activity may be altered by extrahepatic biliary tract obstruction.

Alterations in pentobarbital pharmacokinetics in response to parenteral and enteral alimentation in the rat

Recent in vitro observations suggest that the intestine, in addition to the liver, may be an important organ of first-pass drug metabolism. While a variety of changes in intestinal morphology and function in response to continuous parenteral and enteral nutrition have been documented, the effect of different routes of alimentation on intestinal drug metabolism has not been previously investigated. Objectives of this study were to assess the contribution of intestinal pentobarbital metabolism to overall in vivo pentobarbital pharmacokinetics in the rat and to determine if differences in pentobarbital pharmacokinetics were seen between parenterally and enterally nourished animals. After 7 days of continuous infusion of amino acid-glucose mixture via a gastric or jugular vein catheter, pharmacokinetic parameters were determined after 40 mg/kg of pentobarbital was given orally or into the portal or femoral vein. Reduced systemic availability of pentobarbital after oral administration as compared to portal vein injection was seen in both alimentation groups indicating that significant intestinal metabolism of pentobarbital occurred in vivo. Total area under the pentobarbital plasma concentration-time curve was significantly greater in parenterally nourished animals as compared with enterally alimented animals after oral, portal vein and systemic vein drug administration. Differences in pentobarbital, pharmacokinetics between the two alimentation groups appeared to be primarly due to effects on hepatic pentobarbital metabolism. While the mechanism producing these changes has not been defined, differences in gut hormones release and/or pancreatic secretion in response to the two routes of alimentation may be contributory. The widespread use of enteral and parenteral alimentation in clinical medicine suggests that studies to determine if nutrition route of administration similarly influences drug metabolism in humans may be indicated.

Effects of short-term dietary exposure to polychlorinated biphenyls on pharmacokinetics of intravenous pentobarbital in rats

The intravenous pharmacokinetics of pentobarbital (30 mg/kg as pentobarbital sodium) in rats were studied at 0, 1, 2, 3, and 10 days after pretreatment with 0, 1, 5, 25, and 125 ppm of polychlorinated biphenyls in food. The polychlorinated biphenyls then were removed from the food, and the residual effects of the exposure on pentobarbital pharmacokinetics were studied at 15, 25, 45, and 70 days after initiation of the polychlorinated biphenyl exposure. The pharmacokinetics of pentobarbital were approximated to a one-compartment model. After pretreatment at 2 and 5 ppm for up to 10 days, all pentobarbital pharmacokinetic parameters obtained were comparable to control values. Pretreatment at 125 ppm significantly reduced the biological half-life and raised the total body elimination rate constant, total body clearance, and intrinsic clearance of pentobarbital after a 1-day exposure; all parameters apparently reached a new steady-state value by Days 5--10,. Enhanced pentobarbital elimination at 25 ppm was observed after a 3-day exposure, but, again, the elimination parameters appeared to have reached a steady state after 5--10 days of pretreatment. Upon removal of the polychlorinated biphenyls, the various pharmacokinetic parameters showed a lag phase prior to a gradual return to control values. The study shows that intrinsic clearances rather than total body clearances or half-lives are more appropriate in assessing enzymatic induction in agents undergoing facile liver metabolic clearance that borders on blood flow rate dependency.

Effect of short-term exposure to polychlorinated biphenyls on first-pass metabolism of pentobarbital in rats

The enhancement of the first-pass metabolism of orally administered pentobarbital in rats was examined after a 10-day exposure to food contaminated with polychlorinated biphenyls at 25 and 125 ppm. The degree of the first-pass effect and the influence of the polychlorinated biphenyl exposure were quantitated by comparing the areas under the plasma concentration--time curves after oral and intravenous dosing in control and treated animals. By using the clearance model and assuming that pentobarbital was eliminated totally by liver metabolism, the experimentally determined oral availability was predicted adequately from both the oral and intravenous data. The enhanced first-pass effect was principally in the intrinsic clearance term, although liver blood flow rates also appeared to be enhanced in animals treated with polychlorinated diphenyls at 125 ppm.

The effect of age on the plasma protein binding of pentobarbitone in the mouse. A brief note

Old mice show an increased sensitivity to parenteral pentobarbitone compared with young adult mice, despite similar plasma concentrations of the drug. One factor may be an alteration in the binding of barbiturate to the plasma protein, perhaps consequent on reduced hepatic synthesis of plasma protein with advancing age. As part of a study of the effect of age upon the pharmacological and adaptive response to barbiturates, binding of pentobarbitone to plasma proteins from mice of different ages was measured by equilibrium dialysis in the presence of a standard concentration of the drug. The total plasma protein concentration was measured and found to be the same in both age groups. The plasma protein binding of pentobarbitone was found to correlate significantly with the plasma albumin concentration, which was lower in the older mice. However, there was no significant overall difference in pentobarbitone binding between old and young mice. Pretreatment of the mice with phenobarbitone for 21 days had no effect upon the capacity for plasma protein binding of pentobarbitone in either age group. Thus, it seems unlikely that the increased sensitivity of older mice to pentobarbitone can be explained in terms of altered plasma protein binding of the drug.

Alteration of pharmacokinetic parameters for pentobarbital by ischemic stroke and reversion to normal by dexamethasone treatment

The values of the pharmacokinetic parameters for pentobarbital were determined in 18 cats, 12 of which were subjected to acute ischemic stroke by ligation of the left middle cerebral artery (LMCA). All 18 ats received 50 mg/kg sodium pentobarbital during operation. The following three experimental groups were formed: control (sham-operated); ischemic stroke plus administration of 4 mg/kg dexamethasone; and ischemic stroke without dexamethasone administration. Ischemic stroke significantly prolonged the plasma half-life of pentobarbital, but concurrent administration of dexamethasone prevented this effect. Ischemic stroke significantly reduced the plasma clearance of pentobarbital, but dexamethasone prevented this reduction. Ischemic stroke significantly increased the area under the plasma pentobarbital concentration-time curve, but dexamethasone prevented this increase. Ischemic stroke significantly reduced the volume of distribution, but dexamethasone did not prevent this reduction. The alterations of the value of these pharmacokinetic parameters for pentobarbital by ischemic stroke and reversion to normal by dexamethasone treatment are discussed in the light of certain known circulatory changes which occur secondary to ischemic stroke and dexamethasone treatment.

Enhanced sensitivity to pentobarbital in haloperidol or pimozide treated mice and rats

The influence of intraperitoneal administration of two neuroleptic drugs, haloperidol and pimozide (2.5 and 5.0 mg/kg) on pentobarbital induced narcosis, hypothermia and lethality were investigated in mice and rats. Haloperidol and pimozide administered 10 min prior to pentobarbital sodium (60 mg/kg) injection in rats increased significantly the onset time and duration of sleep. Both neuroleptic drugs also enhanced the intensity of hypothermic response to pentobarbital (50 mg/kg). Similar enhancement of narcosis and hypothermia to pentobarbital (75 mg/kg) was observed in haloperidol and pimozide pretreated mice. Pimozide pretreatment decreased the LD50 value of pentobarbital in mice. Brain and plasma levels of pentobarbital in haloperidol and pimozide treated rats on awakening were lower than in the corresponding saline treated rats. Brain and plasma levels determined at identical time interval in saline and neuroleptic treated rats showed similar results. These data indicate that disposition of pentobarbital cannot explain its enhanced pharmacological effects in haloperidol or pimozide treated animals but the brain sensitivity to pentobarbital is altered. These studies suggest an interaction between pentobarbital and neuroleptic drugs which may have clinical relevance.

Multidose studies in the human metabolism of pentobarbitone

The metabolism of pentobarbitone has been investigated in two healthy volunteers, and the urinary excretion of unchanged drug, and the products of omega- and (omega-1)-oxidation, quantified for four days after each of three doses to each volunteer. The rates of excretion are discussed in terms which include enzyme induction effects.

Brain level of pentobarbital is the primary determinant for the development of hypnotic of hypnotic tolerance in mice

Controlling the duration of hypnotic effect of pentobarbital by simultaneously administered bemegride, the relationship between the duration of hypnosis and the degree of developed tolerance after acute or chronic treatment was investigated in mice. Bemegride attenuated the hypnotic effect of pentobarbital, but neither the brain level of pentobarbital nor the development of tolerance was modified by bemegride, indicating that the brain level of pentobarbital is the primary determinant for the production of tolerance and full duration of hypnosis is not essential in this mechanism.

Model-independent method of analyzing input in linear pharmacokinetic systems having polyexponential impulse response II: Numerical evaluation

The investigated method is based on an exact mathematical solution to the deconvolution problem of linear pharmacokinetic systems with a polyexponential impulse response. The accuracy of the method is determined only by how well the curves fitted to the intravenous and absorption data represent the true drug level. Consequently, the method enables objective evaluation of the input. It permits the user to assess whether discrepancies in a calculated input are due to an improper data representation, as judged from the fitted curves, to the inherent nature of the data, or to a violation of the pharmacokinetic assumptions. The method is compared to another method using simulated data containing various degrees of random noise. The accuracy of the two methods was not significantly different and was of the same magnitude as the noise level of the data. The theoretical properties of the two methods and their expected performance in various pharmacokinetic situations are discussed. The method is applied to pentobarbital data from oral and intravenous administrations.

Novel deconvolution method for linear pharmacokinetic systems with polyexponential impulse response

A novel least-squares deconvolution method for estimating the rate and the extent of drug input into the systemic circulation is presented. The method is based on a polyexponential approximation of the impulse response and a polynomial approximation of the input rate. The method, which is readily implemented on a computer using any multiple linear regression program with a zero-intercept option, is compared to two other deconvolution methods using simulated data with various degrees of random noise added. It appears to have several significant advantages. The method is applied to plasma pentobarbital level data from oral and intravenous administration. The assumptions and limitations of deconvolution methods for analyzing drug input into the blood are discussed.

Diazepam receptors on mouse astrocytes in primary cultures: displacement by pharmacologically active concentrations of benzodiazepines or barbiturates

Astrocytes in primary cultures were found to bind large amounts of [3H]diazepam. More than 90% of the total binding is specific, i.e., displaceable by an excess of nonlabeled diazepam. At saturation the specific binding amounts to about 20 pmol/mg protein and the Kd value is 30 nM. Clonazepam and flurazepam displace [3H]diazepam from its specific binding sites; 20-30% displacement is brought about by 0.1-0.3 microM clonazepam, which is similar to the plasma concentrations encountered in epileptic patients treated with this drug. Barbiturates have a similar effect, but considerably higher concentrations are required.

Induction of rat hepatic microsomal enzymes by toxaphene pretreatment

The effects of pretreatment of rats with toxaphene on hepatic drug metabolizing enzymes and several other parameters of the mixed function oxidase system were investigated. Adult male Sprague-Dawley rats were fed diets containing 0, 50, 100, 150 and 200 ppm of toxaphene for 14 days. The body weight gain was unaltered as well as the food consumption in all the toxaphene fed groups. There was no change in the weights of brain, kidney, heart, and testes but the liver weight was significantly increased. The thymus weight in all the toxaphene fed grups was decreased. Hydroxylation of pentobarbital and aniline was significantly enhanced in rats exposed to toxaphene. Ethylmorphine-N-demethylase activity in the toxaphene treated rats was also elevated. Enhanced hydroxylation of pentobarbital was also evident from the decreased sleeping time following pentobarbital administration. Exposure to toxaphene increased cytochrome P-450, NADPH-cytochrome c-reductase and dehydrogenase in hepatic microsomal fractions. The binding of aniline and hexobarbital to microsomes was also enhanced, suggesting that the intermediate steps in the electron-transfer system were increased. In conclusion, pretreatment of rats with toxaphene for fourteen days resulted in the induction of the hepatic mixed function oxidase system.

Effect of different chemicals on thioacetamine-induced liver necrosis

Several inhibitors of cytochrome P-450 mediated oxidative transformations, ethyl 2-diethylaminoethyl-2-phenyl-2-ethylmalonate, ethyl-2-diethyl-aminoethyl-2-ethyl-2-buthylmalonate, 2,4 dichloro-6-phenoxyethyl diethylamine, 2-diethylaminoethyl-2-phenyl- (2-propene)-4-penten-1-oate or 3-amino,1,2,4 triazole were not able to significantly prevent thiocetamide induced necrosis at 24 h as evidenced by isocitric acid dehydrogenase activity or histologically. In contrast, several other sulfur containing compounds, tetraethyl thiuramidisulfide, diethyldithiocarbamic acid, thiourea or 1-methyl-2-mercaptoimidazole, which are inhibitors of non-cytochrome P-450 dependent amine oxidase systems, significantly prevented thioacetamide induced liver necrosis at 24 h. Notwithstanding, diphenhydramine, nicotinamide, trimethylamine and imipramine, which are substrates of this amino oxidase system, do not protect. All the chemicals tested prolonged the pentobarbital sleeping time, but there is no correlation between the intensity of this effect and their ability for preventing thioacetamide liver necrosis. These observations suggest that cytochrome P-450 does not play a major role in the activation of thioacetamide to a proximal or an ultimate necrogenic metabolite. Other microsomal enzymes metabolizing sulfur compounds could be involved in the major activation process.

The inhibition and potentiation of procarbazine on hepatic mixed-function oxidases in phenobarbital tolerant and nontolerant mice

The effect of procarbazine on mixed-function oxidases was investigated in naive and pentobarbital tolerant mice. In mice receiving procarbazine, 200 mg/kg, i.p. 1 hr earlier, metabolisms of pentobarbital, aniline and ethylmorphine in vitro and cytochrome P-450 content of hepatic microsomes were significantly decreased. The drug binding of either aniline or pentobarbital to cytochrome P-450 was also decreased. However, procarbazine failed to exert this effect after the enzymes had been induced by continuous administration of pentobarbital. Interestingly, procarbazine enhanced the barbiturate induced hepatic microsomal mixed-function oxidase activities when it was administered before the implantation of pentobarbital pellet. Both cytochrome P-450 and cytochrome b5 content after pentobarbital pellet implantation were further increased by pretreatment with procarbazine. This finding was further substantiated by the increase in pentobarbital and aniline binding to cytochrome P-450. The present studies may provide another model for studying the nature of hepatic mixed-function oxidase induction process.