In vivo imaging of translocator protein, a marker of activated microglia, in alcohol dependence.

Neuroinflammation may be a critical component of the neurobiology of alcohol use disorders, yet the exact nature of this relationship is not well understood. This work compared the brain and peripheral immune profile of alcohol-dependent subjects and controls. Brain levels of 18-kDa translocator protein (TSPO), a marker of microglial activation and neuroinflammation, were measured with [11C]PBR28 positron emission tomography imaging in 15 healthy controls and 15 alcohol-dependent subjects. Alcohol-dependent subjects were imaged 1-4 days (n=14) or 24 days (n=1) after their last drink. Linear mixed modeling of partial-volume-corrected [11C]PBR28 data revealed a main effect of alcohol dependence (P=0.034), corresponding to 10% lower TSPO levels in alcohol-dependent subjects. Within this group, exploratory analyses found a negative association of TSPO levels in the hippocampus and striatum with alcohol dependence severity (P<0.035). Peripheral immune response was assessed in a subset of subjects by measuring cytokine expression from monocytes cultured both in the presence and absence of lipopolysaccharide. Peripheral monocyte response to lipopolysaccharide stimulation was lower in alcohol-dependent subjects compared with controls for the proinflammatory cytokines interleukin-6 and interleukin-8. Thus, alcohol-dependent individuals exhibited less activated microglia in the brain and a blunted peripheral proinflammatory response compared with controls. These findings suggest a role for pharmaceuticals tuning the neuroimmune system as therapeutics for alcohol dependence.

The clinical utility of the Medication Adherence Questionnaire (MAQ) in an alcohol pharmacotherapy trial.

BACKGROUND: Medication nonadherence is a ubiquitous problem in pharmacology treatment for alcohol use disorders. Unintentional and purposeful nonadherence as measured by the Medication Adherence Questionnaire (MAQ) has been shown to predict problems with medication adherence; however, feedback from the MAQ has never been incorporated into a behavioral intervention to facilitate medication adherence. We assessed the integration of the MAQ into medical management (MM), a counseling approach frequently employed in conjunction with alcohol pharmacotherapy, to determine whether prior patterns of nonadherence could be addressed effectively to promote medication adherence. METHODS: We conducted a post-hoc analysis of data from 131 alcohol dependent smokers who participated in a double blind, placebo controlled study of varenicline for the treatment of alcohol dependence. At baseline, participants completed a single administration of the MAQ, which asks 2 questions about unintentional nonadherence (e.g., forgetting) and 2 questions about purposeful nonadherence (e.g., stopping because feeling good or feeling bad). Based on these responses, participants were divided into 1 of 3 three categories. Adherent (n=60), Unintentional or Purposeful Nonadherent (n=50) and Unintentional and Purposeful Nonadherent (n=21). Over the course of the 16-week treatment period, patients were expected to participate in 12 medical management (MM) sessions; a brief psychosocial treatment. Feedback based on the MAQ responses was integrated into the MM sessions to facilitate medication and treatment adherence. RESULTS: The 3 adherence groups were compared on baseline characteristics, medication adherence, treatment attendance and end-of-treatment patient ratings of treatment helpfulness. Baseline demographics and characteristics were not significantly different among the three categories. We found no statistically significant differences among the three groups with respect to pill adherence, treatment attendance, and treatment satisfaction ratings. CONCLUSIONS: The findings suggest that the incorporation of MAQ feedback into the MM approach could be effective in mitigating risks associated with prior patterns of nonadherence suggesting that further testing of the integrated behavioral approach is warranted.

Naloxone challenge in smokers. Preliminary evidence of an opioid component in nicotine dependence.

BACKGROUND: This study used an opioid antagonist challenge procedure to evaluate the responsivity of the endogenous opioid system in nicotine-dependent individuals, as evidenced by naloxone-induced alterations in both behavioral (withdrawal, craving) and neuroendocrine (cortisol levels) parameters. METHODS: Twenty subjects (9 smokers and 11 nonsmokers) participated in 4 laboratory sessions during which they were challenged with 0, 0.8, 1.6, or 3.2 mg/70 kg of naloxone and then monitored for 1 hour for subjective signs and symptoms of opiate-like withdrawal, nicotine craving, and alterations in cortisol levels. RESULTS: Nicotine-dependent subjects evidenced naloxone dose-dependent increases in withdrawal signs and symptoms. Lower doses of naloxone also produced increases in urges to smoke (craving) and tiredness in smokers. Smokers, when compared with nonsmokers, had lower prenaloxone baseline levels of cortisol and attenuated cortisol release in response to challenge with naloxone. CONCLUSIONS: These results provide preliminary evidence to suggest that long-term exposure to cigarette smoke is associated with alterations in the responsivity of the endogenous opioid system and the hypothalamic-pituitary-adrenal axis that may contribute to the development of nicotine dependence.

Naltrexone and coping skills therapy for alcohol dependence. A controlled study.

Ninety-seven alcohol-dependent patients were treated for 12 weeks in a double-blind, placebo-controlled study evaluating naltrexone and two manual guided psychotherapies in the treatment of alcohol dependence. Patients were randomized to receive either naltrexone or placebo and either coping skills/relapse prevention therapy or a supportive therapy designed to support the patient's own efforts at abstinence without teaching specific coping skills. Naltrexone proved superior to placebo in measures of drinking and alcohol-related problems, including abstention rates, number of drinking days, relapse, and severity of alcohol-related problems. Medication interacted with the type of psychotherapy received. The cumulative rate of abstinence was highest for patients treated with naltrexone and supportive therapy. For those patients who initiated drinking, however, patients who received naltrexone and coping skills therapy were the least likely to relapse.

Six-month follow-up of naltrexone and psychotherapy for alcohol dependence.

BACKGROUND: The goal of this study was to examine the persistence of naltrexone's effects on drinking outcomes among alcoholics following discontinuation of treatment and to determine whether coping skills therapy improves long-term outcomes compared with supportive therapy. METHODS: Eighty of 97 alcohol-dependent subjects randomized to receive naltrexone or placebo and either coping skills therapy or supportive therapy for 12 weeks were assessed at a 6-month off-treatment follow-up. RESULTS: Subjects who received naltrexone were less likely to drink heavily or to meet criteria for alcohol abuse or dependence than subjects who received placebo. The effect of naltrexone therapy on abstinence rates persisted only through the first month of follow-up. Coping skills therapy was associated with decreased levels of drinking among subjects who received placebo. Psychotherapy condition, however, did not predict alcohol diagnosis at follow-up. CONCLUSIONS: Some but not all of the benefits resulting from short-term naltrexone treatment persist after discontinuation of treatment. The findings suggest that continued treatment with naltrexone may be beneficial for some patients.

Familial transmission of substance use disorders.

BACKGROUND: There is increasing evidence that substance use disorders are familial and that genetic factors explain a substantial degree of their familial aggregation. To perform a controlled family study of probands with several different predominant drugs of abuse, including opioids, cocaine, cannabis, and/or alcohol. METHODS: The subjects for the present study included 231 probands with dependence on opioids, cocaine, cannabis, and/or alcohol and 61 control probands, and their 1267 adult first-degree relatives. Diagnostic estimates were based on semistructured diagnostic interviews and/or structured family history interviews regarding each proband, spouse, and adult first-degree relative. The interview data were reviewed blindly and independently by clinicians with extensive experience in the evaluation and treatment of substance use disorders. RESULTS: There was an 8-fold increased risk of drug disorders among the relatives of probands with drug disorders across a wide range of specific substances, including opioids, cocaine, cannabis, and alcohol, which is largely independent from the familial aggregation of both alcoholism and antisocial personality disorder. There was also evidence of specificity of familial aggregation of the predominant drug of abuse. CONCLUSIONS: Elevation in risk of this magnitude places a family history of drug disorder as one of the most potent risk factors for the development of drug disorders. These results suggest that there may be risk factors that are specific to particular classes of drugs as well as risk factors that underlie substance disorders in general.

Experience of a "slip" among alcoholics treated with naltrexone or placebo.

OBJECTIVE: This study tested the hypothesis that naltrexone reduces relapse rates among alcoholics by modifying the reinforcing effects of initial alcohol consumption and alcohol-induced craving. METHOD: Sixteen alcoholic patients treated with naltrexone and 27 treated with placebo who participated in a 12-week clinical trial reported retrospectively on their subjective responses to their first episode of a lapse into alcohol consumption and on their reasons for terminating the drinking episode. RESULTS: Compared to the subjects who received placebo, the subjects who received naltrexone reported lower levels of craving for alcohol and were more likely to give reasons for terminating drinking that were consistent with decreased incentive to drink. CONCLUSIONS: These findings support the hypothesis that a central effect of naltrexone is the modification of alcohol-induced craving.

Gender-related differences in the characteristics of problem gamblers using a gambling helpline.

OBJECTIVE: The characteristics of male and female gamblers utilizing a gambling helpline were examined to identify gender-related differences. METHOD: The authors performed logistic regression analyses on data obtained in 1998-1999 from callers to a gambling helpline serving southern New England. RESULTS: Of the 562 phone calls used in the analyses, 349 (62.1%) were from male callers and 213 (37.9%) from female callers. Gender-related differences were observed in reported patterns of gambling, gambling-related problems, borrowing and indebtedness, legal problems, suicidality, and treatment for mental health and gambling problems. Male gamblers were more likely than female gamblers to report problems with strategic or "face-to-face" forms of gambling, e.g., blackjack or poker. Female gamblers were more likely to report problems with nonstrategic, less interpersonally interactive forms of gambling, e.g., slot machines or bingo. Female gamblers were more likely to report receiving nongambling-related mental health treatment. Male gamblers were more likely to report a drug problem or an arrest related to gambling. High rates of debt and psychiatric symptoms related to gambling, including anxiety and depression, were observed in both groups. CONCLUSIONS: Individuals with gambling disorders have gender-related differences in underlying motivations to gamble and in problems generated by excessive gambling. Different strategies may be necessary to maximize treatment efficacy for men and for women with gambling problems.

A preliminary investigation of the management of alcohol dependence with naltrexone by primary care providers.

PURPOSE: To describe a preliminary investigation of a model of naltrexone therapy and counselling for use by primary care providers and evaluate its impact on drinking behaviors in a cohort of alcohol-dependent subjects. PATIENTS AND METHODS: The subjects enrolled in this study were 29 alcohol-dependent individuals. They were managed within a primary care treatment model located at a university-affiliated substance research program in New Haven, Connecticut. Subjects were assigned to a primary care provider for treatment of their alcohol dependence and were placed on naltrexone at a dose of 50 mg per day. They were seen for an initial "new patient" visit and 7 "brief" follow-up visits during the 10-week study. The primary outcomes for this study were completion of treatment, change in drinking behaviors from baseline, change in liver enzymes from baseline, provider ratings of improvement, and patient ratings of improvement and satisfaction with treatment. RESULTS: Of the 29 subjects: 21 (72%) completed treatment, and 10 (35%) relapsed to heavy drinking. All drinking behaviors improved significantly from baseline: percent of days abstinent increased from 36.6% to 88.8% (P < 0.0001), percent days abstinent from heavy drinking increased from 48.7% to 97.3% (P < 0.0001), and mean number of drinks per occasion decreased from 9.5 to 2.5 (P < 0.0001). The mean serum gamma glutamyl transferase (GGT) for the group decreased from 67.1 U/L to 45.3 U/L (P < 0.0001). CONCLUSIONS: In this preliminary investigation, treatment of alcohol dependence with our model of naltrexone and counselling by primary care providers appeared to be both feasible and effective.

Triazolinone biphenylsulfonamides as angiotensin II receptor antagonists with high affinity for both the AT1 and AT2 subtypes.

Angiotensin II (AII), the endogenous peptide ligand of the AII receptor, has equivalent high affinity for both the AT1 and AT2 receptor subtypes while most of the reported nonpeptide AII antagonists are AT1-selective. In an effort to identify dual AT1/AT2 nonpeptide AII antagonists, we have pursued modifications of previously prepared trisubstituted 1,2,4-triazolinone biphenylsulfonamides which exhibited subnanomolar in vitro AT1 (rabbit aorta) AII antagonism and AT2 (rat midbrain) IC50 values of < 40 nM. Present results show that a suitable amide (or reversed amide) side chain appropriately positioned on the N2-aryl group of these compounds gave > 15-fold enhancement in AT2 binding affinity without sacrificing nanomolar AT1 potency (IC50). This added amide, combined with an appropriate choice of the N-substituent on the sulfonamide and the ortho substituent on the N2-aryl group, led to an analogue (46, L-163,-007) which exhibited subnanomolar AT1 binding affinity and an AT2/AT1 IC50 ratio of 3. This compound showed excellent iv activity at 1 mg/kg and oral efficacy at 3 mg/kg with > 6 h duration in a conscious rat model. Available data suggest that the newly introduced amide side chain, mandatory for low nanomolar binding affinity at the AT2 receptor, is well-tolerated by the AT1 receptor and has minimal effect on the in vivo properties of these molecules.

Potent and orally active angiotensin II receptor antagonists with equal affinity for human AT1 and AT2 subtypes.

In order to block the effects induced by the interactions between angiotensin II (AII) and both AT1 and AT2 receptors, we have pursued the discovery of orally active non-peptide AII antagonists that exhibit potent and equal affinity for human AT1 and AT2 receptor subtypes. A series of previously prepared nanomolar (IC50) trisubstituted 1,2,4-triazolinone biphenyl-sulfonamide dual-acting AII antagonists has been modified at five different positions in order to increase AT2 binding affinity, maintain AT1 activity, and reduce the human adrenal AT2/AT1 potency ratio (IC50 ratio) from > or = 10. The targeted human adrenal potency ratio of < or = 1 was achieved with a number of compounds possessing an ethyl group at C5 of the triazolinone and a 3-fluoro substituent at the N4-biarylmethyl moiety. The most favored of these was compound 44 which exhibited subnanomolar potency at both the AT1 (rabbit aorta) and AT2 (rat midbrain) receptors, with a slight preference for the latter, and had a human adrenal AT2/AT1 IC50 ratio of 1. This tert-butyl sulfonylcarbamate with an N2-[2-bromo-5-(valerylamino)phenyl] substituent had excellent iv activity at 1 mg/kg (100% peak inhibition, > or = 4 h duration of action) and is orally active at 3 mg/kg with > 6 h duration of action in a conscious rat model. The present study shows that the NH of the amide on the N2-aryl moiety is not required for subnanomolar binding affinity to either receptor subtype, although a keto functionality at this position is essential for acceptable AT2 binding. Receptor-ligand binding interactions derived from the structure-activity relationships are discussed with respect to both receptor subtypes.

In vitro and in vivo evaluation of dihydropyrimidinone C-5 amides as potent and selective alpha(1A) receptor antagonists for the treatment of benign prostatic hyperplasia.

alpha(1) Adrenergic receptors mediate both vascular and lower urinary tract tone, and alpha(1) receptor antagonists such as terazosin (1b) are used to treat both hypertension and benign prostatic hyperplasia (BPH). Recently, three different subtypes of this receptor have been identified, with the alpha(1A) receptor being most prevalent in lower urinary tract tissue. This paper explores 4-aryldihydropyrimidinones attached to an aminopropyl-4-arylpiperidine via a C-5 amide as selective alpha(1A) receptor subtype antagonists. In receptor binding assays, these types of compounds generally display K(i) values for the alpha(1a) receptor subtype <1 nM while being greater than 100-fold selective versus the alpha(1b) and alpha(1d) receptor subtypes. Many of these compounds were also evaluated in vivo and found to be more potent than terazosin in both a rat model of prostate tone and a dog model of intra-urethral pressure without significantly affecting blood pressure. While many of the compounds tested displayed poor pharmacokinetics, compound 48 was found to have adequate bioavailability (>20%) and half-life (>6 h) in both rats and dogs. Due to its selectivity for the alpha(1a) over the alpha(1b) and alpha(1d) receptors as well as its favorable pharmacokinetic profile, 48 has the potential to relieve the symptoms of BPH without eliciting effects on the cardiovascular system.

Integration of opioid antagonists and psychosocial therapy in the treatment of narcotic and alcohol dependence.

Numerous studies suggest that an integration of pharmacologic, psychological, and social therapies may lead to improved treatment outcomes for alcohol-dependent patients. This article discusses studies that show the benefits of treating opiate addiction and alcohol dependence with a combination of naltrexone and psychosocial therapies. It also reviews clinical strategies that may maximize the effectiveness of combining pharmacologic and psychosocial therapies for alcoholism. By matching patients with treatments and combining pharmacologic and psychosocial therapies, health care professionals may help alcohol-dependent patients avoid relapse and achieve sobriety. Determining the optimal amount of time an alcohol-dependent patient should be treated with naltrexone requires further study. The value of initiating naltrexone therapy during inpatient treatment should also be explored.

Measurement of compliance with naltrexone in the treatment of alcohol dependence: research and clinical implications.

BACKGROUND: Medication compliance is a critical issue in pharmacotherapy. This study evaluated the clinical utility of the Medication Event Monitoring System (MEMS), a newer method for monitoring medication compliance, compared with pill count, a traditional measure, in a sample of patients treated for alcohol dependence with naltrexone. METHOD: Ninety-three outpatients meeting DSM-III-R criteria for alcohol dependence participated in a 10-week open-label study of naltrexone. They were provided with naltrexone, 50 mg daily, and concurrent counseling. Measures of medication compliance and drinking during treatment were collected every 2 weeks. RESULTS: Pill count yielded a significantly (p < .001) higher estimate of compliance (87.6%+/-18.1%) than the MEMS (80.4%+/-20.6%). However, the estimate of compliance obtained with the MEMS was more consistently correlated with treatment outcome (percentage of days abstinent, percentage of heavy drinking days, and mean alcohol amount consumed per drinking occasion) than the pill count compliance rate. In addition, classification of the sample into compliant and less compliant groups using the MEMS data yielded groups that differed more clearly on drinking outcomes than did stratification on the basis of pill count. CONCLUSION: In pharmacotherapy research, the MEMS may provide more reliable and valid information about subjects' medication compliance than pill count. Clinically, information obtained with the MEMS could be used to provide feedback to patients about their pill-taking behavior to enhance compliance and overall outcome of therapy.

Effects of ethanol on the acoustic startle reflex in humans.

The effect of ethanol on human sensorimotor reactivity was assessed by examining the acoustic startle response. Twelve healthy normal subjects participated in a startle reflex experiment in which placebo or ethanol were given on separate days. Three types of startle probes were used. They consisted of pulse-alone bursts of white noise at 108 dB(A) and 99 dB(A) to explore startle reactivity, and of a 108 dB(A) pulse preceded by a 85 dB(A) prepulse stimulus (prepulse+pulse) to assess prepulse inhibition. Startle amplitude was larger to the 108 dB(A), compared to the 99 dB(A) pulse-alone probes. The prepulse stimulus significantly reduced the amplitude of the startle reflex elicited by the subsequent 108 dB(A) stimulus. The amplitude of the startle response was dramatically reduced by acute ethanol. The effects of ethanol on prepulse inhibition could not be assessed because the startle response was too small in the ethanol condition.

Effects of ethanol on the processing of low probability stimuli: an ERP study.

The effect of a moderate dose of ethanol on the processing of low probability task-relevant and task-irrelevant stimuli was investigated using event-related potentials (ERPs). Sixteen subjects received alcoholic and placebo beverages on alternate days. ERPs were recorded from 15 locations on the scalp. The subjects were asked to press a button upon detection of rare target stimuli embedded among frequent standard and rare "novel" stimuli. Ethanol 1) reduced the amplitude of P3 to novel stimuli, but not P3 to target stimuli, 2) did not affect the mismatch negativity, and 3) delayed P3 latency and reaction time independently. These results suggest that 1) the processing of rare task-irrelevant stimuli is more vulnerable to the effects of ethanol than is the processing of task-relevant stimuli, and 2) ethanol impacts stimulus evaluation time and response production stages of information processing.

Psychological stress, drug-related cues and cocaine craving.

RATIONALE: While several environmental situations may produce cocaine craving, there is little research on whether patterns of drug cue reactivity are similar across different environmental situations. OBJECTIVE: This study examined whether two different environmental situations, psychological stress and drug cues, produce similar or varying patterns of cue reactivity in 20 cocaine dependent individuals. METHODS: All subjects participated in a single laboratory session and were exposed to stress, drug cues and neutral-relaxing imagery conditions. Cocaine and alcohol craving, emotion state ratings, subjective anxiety, heart rate and salivary cortisol measures were assessed. RESULTS: Significant increases in cocaine and alcohol craving were observed with stress and drug cues imagery but not with neutral-relaxing imagery. In addition, stress and drug cues situations produced similar increases in subjective anxiety, heart rate and salivary cortisol levels. Significant increases in negative emotion ratings and decreases in positive emotion ratings were found for stress and drug cues conditions as compared to the neutral condition. CONCLUSIONS: The findings indicate that a similar and comparable pattern of cue reactivity is induced by stress and drug cue manipulations. Furthermore, the comparable increases in subjective anxiety and negative affect observed with stress-induced and drug cue-induced craving provides support for the negative reinforcement model of drug craving and relapse. The negative affectivity co-occurring with the craving state appears to be an important target in the development of new treatments for cocaine dependence.

Characterization of specific binding of [125I]L-762,459, a selective alpha1A-adrenoceptor radioligand to rat and human tissues.

L-762,459 ((+/-)1-(3-¿[5-carbamoyl-2-2-[(4-hydroxy-3-iodobenzimidoyl)-amino] -ethoxy-methy¿-6-methyl-4-(4-nitropheny)-1,4-dihydropyridine -3-carbonyl]-amino¿-propyl)-4-phenyl-1-piperidine-4-carboxylic acid methyl ester), an analog of a series of dihydropyridines previously reported to be selective alpha1A-adrenoceptor subtype antagonists was found to have alpha1A-adrenoceptor subtype selectivity (Ki (nM), la = 1.3, lb = 240, Id = 280). Specific [125I]L-762,459 binding was detected in rat cerebral cortex, hippocampus, vas deferens, kidney, heart and prostate tissues known to contain the alpha1A-adrenoceptor subtype, but not in tissues known to contain alpha1B-adrenoceptor (spleen, liver) and alpha1D-adrenoceptor (aorta). Scatchard analysis of [125I]L-762,459 binding in rat cerebral cortex and prostate indicated a single binding site with a Kd of 0.7 nM and Bmax of 11 (cerebral cortex) and 1 (prostate) pmole/g tissue. Specific and saturable [125I]L-762,459 binding was also found in human cerebral cortex, liver, prostate and vas deferens (Kd = 0.2-0.4 nM, Bmax = 0.4-4 pmole/g tissue). The specific binding in rat and human tissues was competed by non-selective alpha1-adrenoceptor compounds (Ki values in nM: prazosin (0.14-1.2), terazosin (1.8-5.9) and phentolamine (2.4-11)) and selective alpha1A-adrenoceptor compounds [Ki values in nM: (+) niguldipine (0.04-1.2) and SNAP 5399 ((+/-)-2-((2-aminoethyl)oxy)methyl-5-carboxamido-6-ethyl-4-(4-nitropheny l)-3-N-(3-(4,4-diphenylpiperidin-1-yl)propyl)carboxamido-1,4-dihyd ropyridine hydrate (0.5-4.8)]. The results were consistent with the selective binding of [125I]L-762,459 to the alpha1A-adrenoceptor. The specific labeling of the alpha1A-adrenoceptor subtype by [125I]L-762,459 may make it a useful tool to localize the distribution of the alpha1A-adrenoceptor.

In vitro pharmacology of an angiotensin AT1 receptor antagonist with balanced affinity for AT2 receptors.

L-163,017 (6-[benzoylamino]-7-methyl-2-propyl-3-[[2'-(N-(3-methyl-1-butoxy) carbonylaminosulfonyl) [1,1']-biphenyl-4-yl]methyl]-3H-imidazo[4,5-b]pyridine) inhibited specific 125I-[Sar1, Ile8]angiotensin II binding to angiotensin AT1 receptor (Ki = 0.11-0.20 nM) in rabbit aorta, rat adrenal and human angiotensin AT1 receptor in CHO (Chinese hamster ovary transformed) cells and to AT2 receptor (Ki = 0.14-0.23 nM) in rat adrenal and brain receptors. L-163,017 also had a high affinity in the presence of bovine serum albumin (2 mg/ml), for angiotensin AT1 and AT2 receptors on human adrenal (Ki 3.9 and 4.3 nM), aorta (Ki 0.45 and 0.96 nM) and kidney (Ki 3.6 and 2.3 nM). The much higher Ki values in human tissues were likely due to the presence of bovine serum albumin in the binding assay buffer since L-163,017 had Ki values of 0.13 +/- 0.04 and 2.0 +/- 0.04 nM in the absence and presence of bovine serum albumin, respectively, in inhibiting 125I-[Sar1,Ile8]angiotensin II binding to angiotensin AT1 receptor in rat adrenal membranes. Scatchard analysis of 125I-[Sar1,Ile8]angiotensin II binding in the presence of bovine serum albumin (2 mg/ml) in rabbit aorta and bovine cerebellum indicated a competitive interaction of L-163,017 with angiotensin AT1 and AT2 receptors (Ki values 2.5 and 2.1 nM respectively). L-163,017 inhibited angiotensin II-induced aldosterone release in rat adrenal demonstrating that L-163,017 acted as a competitive antagonist (pA2 = 9.9) and lacked agonist activity. L-163,017 also inhibited angiotensin II responses in rat vascular tissues. The specificity of L-163,017 was shown by its lack of activity on the above functional responses produced by other agonists and in several binding assays.