Naloxone effects on beta-endorphin, cortisol, prolactin, growth hormone, HVA and MHPG in plasma of normal volunteers

Blunted opioid regulation of the HPA stress response during nicotine withdrawal: therapeutic implications

Endogenous opioids regulate pain, drug reward, and stress responses. We have previously shown reduced hypothalamic-pituitary-adrenal (HPA) responses to psychological stress and to opioid blockade among dependent smokers. In this study, we examined the extent to which biologically confirmed nicotine withdrawal alters endogenous opioid regulation of HPA axis functioning during rest and in response to acute stress. Smokers were randomly assigned to one of two conditions; 24 h withdrawal from all nicotine-containing products (n = 62) or smoking ad libitum (n = 44). A nonsmoking comparison group (n = 43) was also included. Participants (85 males and 64 females) completed two acute stress sessions during which a placebo or 50 mg of naltrexone (opioid antagonist) were administered using a double-blind design. Blood and saliva samples (assayed for cortisol and adrenocorticotropic hormone, i.e. ACTH) and mood measures were obtained during a resting absorption period, after acute stress (public speaking, mental arithmetic, and cold pressor tasks), and during an extended recovery period. Results indicated that opioid blockade (naltrexone) was associated with increased ACTH and cortisol responses to stress, and tobacco withdrawal was associated with blunted hormonal responses. A pattern of sex differences also emerged, with women exhibiting reduced ACTH responses to stress and higher ACTH and plasma cortisol responses to opioid blockade. These results indicated that compared to ad libitum smoking, nicotine withdrawal is associated with blunted opioid modulation of the HPA axis. Sex may modulate these effects. Blunted endogenous opioid regulation may underlie an incentive process that reinforces smoking behavior and may warrant therapeutic attention.

Drug-induced stress responses and addiction risk and relapse

A number of studies have assessed the effects of psychoactive drugs on stress biology, the neuroadaptations resulting from chronic drug use on stress biology, and their effects on addiction risk and relapse. This review mainly covers human research on the acute effects of different drugs of abuse (i.e., nicotine, cannabis, psychostimulants, alcohol, and opioids) on the hypothalamic-pituitary-adrenal (HPA) axis and the autonomic nervous system (ANS) responses. We review the literature on acute peripheral stress responses in naïve or light recreational users and binge/heavy or chronic drug users. We also discuss evidence of alterations in tonic levels, or tolerance, in the latter relative to the former and associated changes in the phasic stress responses. We discuss the impact of the stress system tolerance in heavy users on their response to drug- and stress-related cue responses and craving as compared to control subjects. A summary is provided of the effects of glucocorticoid responses and their adaptations on brain striatal and prefrontal cortices involved in the regulation of drug seeking and relapse risk. Finally, we summarize important considerations, including individual difference factors such as gender, co-occurring drug use, early trauma and adversity and drug use history and variation in methodologies, that may further influence the effects of these drugs on stress biology.

Multiple signaling pathways convey central and peripheral signals to regulate pituitary function: Lessons from human and non-human primate models

The anterior pituitary gland is a key organ involved in the control of multiple physiological functions including growth, reproduction, metabolism and stress. These functions are controlled by five distinct hormone-producing pituitary cell types that produce growth hormone (somatotropes), prolactin (lactotropes), adrenocorticotropin (corticotropes), thyrotropin (thyrotropes) and follicle stimulating hormone/luteinizing hormone (gonadotropes). Classically, the synthesis and release of pituitary hormones was thought to be primarily regulated by central (neuroendocrine) signals. However, it is now becoming apparent that factors produced by pituitary hormone targets (endocrine and non-endocrine organs) can feedback directly to the pituitary to adjust pituitary hormone synthesis and release. Therefore, pituitary cells serve as sensors to integrate central and peripheral signals in order to fine-tune whole-body homeostasis, although it is clear that pituitary cell regulation is species-, age- and sex-dependent. The purpose of this review is to provide a comprehensive, general overview of our current knowledge of both central and peripheral regulators of pituitary cell function and associated intracellular mechanisms, focusing on human and non-human primates.

Naltrexone selectively elevates GABAergic neuroactive steroid levels in heavy drinkers with the Asp40 allele of the OPRM1 gene: a pilot investigation

BACKGROUND

Preclinical studies have implicated GABAergic neurosteroids in behavioral responses to alcohol. Naltrexone is thought to blunt the reinforcing effects of alcohol, and a few studies have found that the effects of naltrexone are moderated by the Asn40Asp polymorphisms of the OPRM1 gene. The present study seeks to integrate these lines of research by testing (i) the moderating role of the functional Asn40Asp polymorphism of the OPRM1 gene on naltrexone-induced alternations in GABAergic neurosteroid levels, namely (3alpha,5alpha)-3-hydroxypregnan-20-one (allopregnanolone, ALLO); and (ii) the combined effects of naltrexone or genotype with alcohol administration on neurosteroid levels in a sample of at-risk drinkers.

METHODS

Participants were 32 (9 females) nontreatment-seeking heavy drinkers who completed a placebo-controlled laboratory study of naltrexone (50 mg/d for 3 days) and provided complete sets of serum samples for ALLO assays before and after alcohol administration under both naltrexone and placebo conditions.

RESULTS

Naltrexone treatment raised ALLO levels among carriers of the Asp40 allele, but not homozygotes for the Asn40 allele. The Asn40Asp polymorphism did not moderate effects of naltrexone on cortisol levels. Ethanol infusion modestly reduced ALLO levels in all subjects, independent of genotype or naltrexone exposure.

CONCLUSIONS

Naltrexone increased ALLO levels among individuals with the Asn40Asp allele suggesting a potential neurosteroid contribution to the neuropharmacological effects of naltrexone among Asp40 carriers.

Acute HPA axis response to naltrexone differs in female vs. male smokers

BACKGROUND

Both opioid antagonist administration and cigarette smoking acutely increase hypothalamic-pituitary-adrenal (HPA) axis activity as measured by adrenocorticotropic hormone (ACTH) and cortisol levels. However, male and female smokers may differ in their response to the opioid antagonist naltrexone, which may be partially mediated by sex differences in HPA axis function. Smokers, as a group, have frequently been shown to have HPA axis dysfunction, which may have relevance to the course and maintenance of nicotine dependence. The purpose of this study was to examine possible sex differences in HPA axis function by comparing stress-hormone response to naltrexone within healthy male and female smokers. Additionally, exploratory analyses compared the combined effects of naltrexone and cigarette smoking on hormonal responsivity between the sexes.

METHOD

Thirty-eight healthy smokers (22 men) were tested in two separate morning sessions after 12h of smoking abstinence. For women, self-reports of menstrual cycle information were obtained prior to each session (date of last menstruation, cycle length, reproductive phase, etc.). Each participant received 50mg naltrexone or placebo capsule (in random order) and plasma levels of ACTH and cortisol were assessed at regular intervals for several hours. A subgroup of 12 participants underwent a similar, additional session in which they smoked a single cigarette three hours after naltrexone administration.

RESULTS

Naltrexone significantly increased ACTH and cortisol levels in women, but not men (DrugxSexxTime, p<0.05). A post hoc analysis suggested that women at an estimated 'high estrogen' phase had a greater cortisol response (DrugxEstrogen level, p<0.05) than those at an estimated 'low estrogen' phase. Exploratory analyses showed that smoking a single cigarette potentiated naltrexone-induced increases in ACTH (p<0.05) and cortisol (p<0.01) in all participants.

CONCLUSION

The findings support the hypothesis that women are more sensitive to opioid antagonism at the level of the HPA axis. Although further studies are needed to examine mechanisms underlying these responses, both results may have clinical implications for the use of naltrexone as a treatment for nicotine dependence.

The effects of opioids and opioid analogs on animal and human endocrine systems

Opioid abuse has increased in the last decade, primarily as a result of increased access to prescription opioids. Physicians are also increasingly administering opioid analgesics for noncancer chronic pain. Thus, knowledge of the long-term consequences of opioid use/abuse has important implications for fully evaluating the clinical usefulness of opioid medications. Many studies have examined the effect of opioids on the endocrine system; however, a systematic review of the endocrine actions of opioids in both humans and animals has, to our knowledge, not been published since 1984. Thus, we reviewed the literature on the effect of opioids on the endocrine system. We included both acute and chronic effects of opioids, with the majority of the studies done on the acute effects although chronic effects are more physiologically relevant. In humans and laboratory animals, opioids generally increase GH and prolactin and decrease LH, testosterone, estradiol, and oxytocin. In humans, opioids increase TSH, whereas in rodents, TSH is decreased. In both rodents and humans, the reports of effects of opioids on arginine vasopressin and ACTH are conflicting. Opioids act preferentially at different receptor sites leading to stimulatory or inhibitory effects on hormone release. Increasing opioid abuse primarily leads to hypogonadism but may also affect the secretion of other pituitary hormones. The potential consequences of hypogonadism include decreased libido and erectile dysfunction in men, oligomenorrhea or amenorrhea in women, and bone loss or infertility in both sexes. Opioids may increase or decrease food intake, depending on the type of opioid and the duration of action. Additionally, opioids may act through the sympathetic nervous system to cause hyperglycemia and impaired insulin secretion. In this review, recent information regarding endocrine disorders among opioid abusers is presented.

The Effects of Naltrexone Among Alcohol Non-Abstainers: Results from the COMBINE Study

These analyses of the COMBINE Study examined the effects of naltrexone among non-abstainers. Given that one of the most well-established mechanisms of action of naltrexone involves blunting of alcohol reward, it is hypothesized that naltrexone should be more effective among individuals who drank during treatment. Participants were 952 (78% of the total COMBINE Study sample) treatment-seeking alcohol-dependent men and women who received pharmacotherapy for alcoholism and drank at least once during the 16-week trial. Mixed model analyses revealed that individuals who drank more regularly during the trial seemed to benefit most from naltrexone and the effects of naltrexone on heavy drinking was significant in treatment months 2 through 4 among individuals who reported drinking on 81, 68, and 60% or more of days, respectively. Those drinking frequencies were observed in 11, 15, and 19% of the sample. Similar effects were not observed for drinks per drinking day. These results suggest that a small subgroup of non-abstainers, composed primarily of very regular drinkers, appears to benefit from naltrexone in reducing heavy drinking days. Naltrexone may be effective in the context of controlled-drinking approaches, even among very frequent drinkers.

Young Investigator Award symposium

This article highlights the research presented at the inaugural meeting of Alcoholism and Stress: A Framework for future Treatment Strategies. This meeting was held on May 6-8, 2008 in Volterra, Italy. It is an international meeting dedicated to developing preventive strategies and pharmacotherapeutic remedies for stress- and alcohol-related disorders. For the first time, the National Institute on Alcohol Abuse and Alcoholism (NIAAA) conferred a Young Investigator Award to promote the work of young researchers and highlight their outstanding achievements in the fields of addiction medicine and stress disorders. The awardees were Dr. Katie Witkiewitz (University of Washington), Dr. Andrew Holmes (NIAAA), Dr. Lara A. Ray (Brown University), Dr. James Murphy (University of Memphis), and Dr. Heather Richardson (The Scripps Research Institute). The symposium was chaired by Drs. Fulton Crews and Antonio Noronha.

Effects of naltrexone on cortisol levels in heavy drinkers

The primary objectives of this study were to: (a) examine the neuroendocrine effects of naltrexone vs. placebo by comparing serum cortisol levels; and (b) test the biobehavioral correlates of naltrexone-induced changes in cortisol. Non-treatment seeking heavy drinkers (n=37) completed two intravenous alcohol administrations, one after naltrexone (50 mg) and one after placebo. Cortisol levels were measured at baseline and after alcohol intake (BrAC=0.06 g/dl) on both sessions, as were subjective responses to alcohol. Analyses revealed that naltrexone significantly raised overall cortisol levels compared to placebo. Cortisol levels decreased during alcohol administration and a stronger decrease was observed in the naltrexone condition. Cortisol levels were, in turn, inversely related to some of alcohol's the reinforcing effects (i.e., alcohol 'high,' vigor) and positively associated with some of its unpleasant effects (i.e., sedation and subjective intoxication). These results suggest that naltrexone alters cortisol levels in heavy drinkers and that its effects on subjective responses to alcohol may be related, in part, to naltrexone's ability to activate the HPA-axis.

Naltrexone attenuates the subjective effects of amphetamine in patients with amphetamine dependence

Amphetamine abuse and dependence is a global health concern with a collateral increase in medical and social problems. Although some of the neurobiological mechanisms underlying amphetamine dependence and its devastating effects in humans are known, the development of rational and evidence-based treatment is lagging. There is evidence from preclinical studies suggesting that the endogenous opioid system plays a role in mediating some of the behavioral and neurochemical effects of amphetamine in a variety of controlled settings. In the present study we assessed the effects of naltrexone, an opioid antagonist (50 mg) on the subjective physiological and biochemical response to dexamphetamine (30 mg) in 20 amphetamine-dependent patients. Patients received naltrexone/amphetamine followed by placebo/amphetamine, 1 week apart in a randomized double-blind placebo-controlled design. The primary objective of the study was to evaluate the effect of pretreatment with naltrexone on the subjective response to amphetamine, using a Visual Analog Scale. The secondary objective was to investigate the effects of naltrexone on physiological and biochemical responses to amphetamine, as measured by changes in blood pressure, heart rate, skin conductance, and cortisol. Naltrexone significantly attenuated the subjective effects produced by dexamphetamine in dependent patients (p<0.001). Pretreatment with naltrexone also significantly blocked the craving for dexamphetamine (p<0.001). There was no difference between the groups on the physiological measures. The results suggest that the subjective effects of amphetamine could be modulated via the endogenous opioid system. The potential of naltrexone as an adjunct pharmaceutical for amphetamine dependence is promising.

Effects of mu, kappa, and delta opioid receptor agonists on the function of hypothalamic-pituitary-adrenal axis in monkeys

Opioids can modulate neuroendocrine function. Less is known about the involvement of opioid receptor subtypes in the stimulatory effects of opioids on the primate hypothalamic-pituitary-adrenal (HPA) axis. The aim of this study was to investigate the stimulatory effects of opioids selective for each receptor subtype on plasma adrenocorticotropic hormone (ACTH) and cortisol levels in both male and female monkeys. The blood collection procedure was conducted in home-caged and unanesthetized rhesus monkeys that showed low and stable basal ACTH and cortisol levels. Three opioid receptor agonists, fentanyl, U-50488H, and SNC80, were used in behaviorally active doses; they are highly selective for mu, kappa, and delta opioid receptors, respectively. Plasma samples were collected at multiple time points before and after IV administration of each compound and were quantified by radioimmunoassay. Neither fentanyl (0.0003-0.02mg/kg) nor SNC80 (0.03-0.3mg/kg) changed either ACTH or cortisol basal levels. In contrast, U-50488H (0.01-1mg/kg) dose-dependently stimulated ACTH and cortisol release in both male and female monkeys. Importantly, the stimulatory effects of U-50488H on the secretion of ACTH were blocked by a selective kappa opioid receptor antagonist, nor-Binaltorphimine. The antagonist effect of nor-binaltorphimine lasted up to 20 weeks. These results indicate that only synthetic kappa, but not mu or delta opioid receptor agonists stimulate HPA axis activity after acute administration in primates.

Nalmefene induced elevation in serum prolactin in normal human volunteers: partial kappa opioid agonist activity?

In humans, mu- and kappa-opioid receptor agonists lower tuberoinfundibular dopamine, which tonically inhibits prolactin release. Serum prolactin is, therefore, a useful biomarker for tuberoinfundibular dopamine. The current study evaluated the unexpected finding that the relative mu- and kappa-opioid receptor selective antagonist nalmefene increases serum prolactin, indicating possible kappa-opioid receptor agonist activity. In all, 33 healthy human volunteers (14 female) with no history of psychiatric or substance use disorders received placebo, nalmefene 3 mg, and nalmefene 10 mg in a double-blind manner. Drugs were administered between 0900 and 1000 on separate days via 2-min intravenous infusion. Serial blood specimens were analyzed for serum levels of prolactin. Additional in vitro studies of nalmefene binding to cloned human kappa-opioid receptors transfected into Chinese hamster ovary cells were performed. Compared to placebo, both doses of nalmefene caused significant elevations in serum prolactin (p<0.002 for nalmefene 3 mg and p<0.0005 for nalmefene 10 mg). There was no difference in prolactin response between the 3 and 10 mg doses. Binding assays confirmed nalmefene's affinity at kappa-opioid receptors and antagonism of mu-opioid receptors. [(35)S]GTPgammaS binding studies demonstrated that nalmefene is a full antagonist at mu-opioid receptors and has partial agonist properties at kappa-opioid receptors. Elevations in serum prolactin following nalmefene are consistent with this partial agonist effect at kappa-opioid receptors. As kappa-opioid receptor activation can lower dopamine in brain regions important to the persistence of alcohol and cocaine dependence, the partial kappa agonist effect of nalmefene may enhance its therapeutic efficacy in selected addictive diseases.

Yohimbine-induced withdrawal and anxiety symptoms in opioid-dependent patients

BACKGROUND

Alteration in noradrenergic regulation as well as alteration in the hypothalamic-pituitary-adrenal (HPA) axis have been associated with opioid dependence and acute abstinence symptoms.

METHODS

This double-blind, placebo-controlled study evaluated subjective, physiologic, and biochemical responses to yohimbine (.4 mg/kg, IV) in eight patients receiving methadone and compared results to those from a pool of nine healthy volunteers. All subjects were compared for panic anxiety symptom scale (PASS) scores, systolic and diastolic blood pressure, heart rate, plasma 3-methoxy-4 hydroxyphenethyleneglycol (MHPG), and cortisol.

RESULTS

Yohimbine elicited objective and subjective opioid withdrawal and elevated craving for opioid drugs in methadone patients. Significant yohimbine effects were seen across the combined subject group for PASS, physiologic measures, MHPG, and cortisol. Methadone patients had lower baseline MHPG levels. Methadone group interactions with yohimbine were seen for systolic blood pressure and cortisol levels.

CONCLUSIONS

Methadone-maintained patients are sensitive to the postsynaptic effects of noradrenergic-facilitating medications, experiencing greater physiologic and psychological symptoms, including an increase in craving. The effect on cortisol supports the above conclusion and is consistent with HPA axis perturbation in opioid dependence as reported in other studies and extends these observations to stable methadone-maintained patients. Medications that increase synaptic noradrenaline should be used with care in opioid-dependent patients.

Opioid antagonists and alcoholism treatment

The increasing evidence for a neurobiologic basis for alcoholism has spurred the search for pharmacologic agents to treat alcohol abuse. The complex set of symptoms and behaviors that characterizes alcoholism has been linked to dopaminergic and opioid neurotransmitter systems, suggesting that opioid antagonists, such as naltrexone, may alter the positive reinforcement effects and craving involved in alcoholism. Laboratory and clinical investigations of naltrexone have demonstrated the potential for this agent to reduce craving, increase the aversive effects of alcohol, decrease drinking days, and increase abstinence. While naltrexone and other opioid antagonists, such as nalmefene, may be effective components of an alcohol-treatment program, they should only be used in combination with psychosocial interventions, such as support groups and psychotherapy.

Physiologic and neuroendocrine responses to intravenous naloxone in subjects with Alzheimer's disease and age-matched controls

BACKGROUND

Prior work showed that administration of naloxone HCl had different behavioral effects in patients with Alzheimer's disease (AD) than controls. The aim of the present study was to contrast the physiologic and neuroendocrine responses to administration of a wide range of doses of intravenous naloxone of patients with probable Alzheimer's disease to aged-matched controls.

METHODS

This was a double-blind, placebo-controlled, study of 12 patients with probable Alzheimer's disease and 8 age-matched normal controls who each received intravenous infusions of naloxone HCl on 3 different days in doses of 0.1 mg/kg and 2.0 mg/kg preceded by test doses of 0.5 mcg/kg. Order of treatment condition was randomized. Vital signs and plasma cortisol and prolactin were obtained at regular intervals.

RESULTS

Both groups showed increased cortisol after naloxone 0.1 mg/kg and 2.0 mg/kg (p < .0001), but the increase was significantly greater and longer lived in controls than in patients. Patients, but not controls, also experienced a significant hypothermic response after naloxone 2.0 mg/kg (p < .05). Prolactin, heart rate, and blood pressure did not change following naloxone and did not differ between groups.

CONCLUSIONS

These findings support a growing body evidence that HPA axis activity is increased in AD, and further suggest that at least part of this may be due to decreased opiatergic tonic inhibition.

Nalmefene causes greater hypothalamic-pituitary-adrenal axis activation than naloxone in normal volunteers: implications for the treatment of alcoholism

Among other actions, opioid antagonists modulate the control endogenous opioids exert on the hypothalamic-pituitary-adrenal (HPA) axis. Naloxone, nalmefene, and naltrexone are the opioid antagonists approved for use in man and are primarily mu-opioid selective. Naltrexone and nalmefene have been demonstrated to be useful in the treatment of alcoholism. Compared with naloxone, nalmefene has a longer half-life, is more potent at the mu-receptor, and has a higher affinity for kappa- and delta-opioid receptors. We conducted an inpatient study comparing the effects of 10 and 30 mg doses of intravenous naloxone and nalmefene in normal, nonsubstance nor alcohol-abusing, volunteers. Significant increases in ACTH and cortisol were observed after both antagonists, without an apparent dose-response relationship; however, both doses of nalmefene resulted in greater HPA axis activation than either dose of naloxone (ACTH: p <0.005). These results indicate that kappa- and delta-opioids may play important roles in the regulation of the HPA axis; nalmefene may be useful as both a probe to explore the HPA axis physiology and as a pharmacotherapeutic agent.

Reliability of sequential naloxone challenge tests

To determine the reliability of serial naloxone challenges, five heroin addicts stabilized on methadone were given 0.2 mg naloxone intravenously on three consecutive days. Two-factor ANOVA revealed that the between-subjects effect accounted for at least 63% of the variance in each of the dependent measures, and the effect of challenge number for at most 22%. Withdrawal tended to be slightly more severe for the first challenge. Intraclass correlation coefficients were calculated for the area-under-the-curve of the change from baseline: subject-rated (.74) and observer-rated (.71) withdrawal, pulse (.88), systolic blood pressure (.58), diastolic blood pressure (.85), and skin temperature (.63).

Beta endorphin levels during heroin, methadone, buprenorphine, and naloxone challenges: preliminary findings

Beta endorphin (BE) is a polypeptide agonist for the brain's endogenous opioid system. Levels of BE are elevated by opioid antagonists such as naloxone and depressed by short-acting agonists such as heroin and morphine; they become normalized during steady-state methadone. Buprenorphine (BUP) is a partial opioid agonist whose effects on BE levels were examined in six former heroin addicts and 14 methadone-maintained patients before and after being switched to sublingual BUP 2 mg daily for 1 month. In six former methadone-treated subjects BE levels also were measured after stopping BUP and after naloxone challenge. Levels of BE were not significantly lower in subjects started on BUP after stopping heroin (n = 6) (8.0 versus 8.1 ng/ml) or in subjects started on BUP after stopping methadone (n = 14) (11.6 vs 15.6 ng/ml). However, BE levels were lower on BUP than after naloxone challenge (n = 6) (7.0 versus 34.9 ng/ml). Levels of BE did not significantly change between the first 2 weeks ("early") and "later," although BE levels on methadone significantly correlated with BE levels on BUP in the "early" but not the "later" phase. The BE levels on BUP also did not differ from BE levels of unmedicated normals.

Hypercortisolism after opioid discontinuation in rapid detoxification of heroin addicts

Long-term opioid consumption can induce hypoadrenalism through impairment of the hypothalamic-pituitary-adrenal axis. Results of the present study showed that, in heroin addicts, saliva cortisol concentrations varied according to the amount of recently consumed heroin and the time elapsed since the last self-administration. Hypercortisolism was observed either after abrupt withdrawal of heroin or the last dose of methadone. Post-detoxification hypercortisolism was still present on day 16 after the last opioid consumption, whereas it was not observed in abstinent addicts for a mean period of 4 months. During detoxification treatment, mean AUC8-24 cortisol in saliva of clonidine or guanfacine-treated patients was significantly higher than that in methadone-treated patients. It may be hypothesized that elevated cortisol levels may account for untoward effects of adrenergic agonist therapy which, in turn, may represent an added risk factor for relapse during detoxification. Further studies are necessary to correlate the severity of withdrawal symptoms to cortisol levels in opioid addicts detoxified with alpha 2-adrenergic agonist substitution.

Stimulation of kappa opiate receptors in intestinal wall affects stress-induced increase of plasma cortisol in dogs

In dogs, an acoustic stress (A.S.) produced by hearing of intense music (less than or equal to 90 dB) through earpieces for 1 h induced a 520% maximal rise in plasma cortisol 15-30 min after the beginning of stress. Oral administration of the specific kappa agonists, U-50488 (0.1 mg/kg) and PD 117302 (0.05 mg/kg), 30 min before the A.S. session reduced significantly (P less than 0.01) by 71.2% and 80.9% the maximal increase of plasma cortisol but did not affect the increase observed after intracerebroventricular administration of ovineCRF (100 ng/kg). These effects which are not reproduced by intravenous administration of the drugs at similar doses, were blocked by previous treatment with MR 2266 (0.1 mg/kg) or local anesthesia and vagotomy, suggesting that kappa opioid agonists inhibit the stress-induced activation of the hypothalamo-pituitary-adrenocortical (HPA) system by acting selectively on specific receptors located in the wall of the proximal gut.

Naloxone in moderate dose does not aggravate chronic tension headache

Naloxone per se causes no pain in normal man, indicating that opioidergic antinociceptive systems are not tonically active, but this might not be the case in chronic pain conditions. The present investigation tested the hypothesis that pain in chronic headache is the result of insufficiently attenuated nociceptive impulses. Forty-seven patients suffering from chronic tension headache entered the present double-blind cross-over trial of naloxone 4 mg i.v. versus saline. Adverse effects were negligible. Patients scored headache pain on a 100 mm visual analog scale and change in headache on a 5-point verbal rating scale after 5, 15, 30, 60 and 90 min. Mean arterial blood pressure decreased 4.2 mm Hg (P less than 0.05) after naloxone compared to saline, but naloxone had no effect on headache (P = 0.96). A bimodal distribution of acute pain patients into placebo responders and non-responders has been reported, but our chronic pain patients showed a homogeneous placebo response. Review of the literature indicates that acute clinical pain and stimulation-induced analgesia in experimental pain has a naloxone-responsive component. Chronic pain does not appear to be influenced by naloxone in moderate doses.

Carotid baroreflex sensitivity at rest and during exercise is not influenced by opioid receptor antagonism

Physical effort involves, along with an increase in the plasma concentration of beta-endorphin, profound cardiovascular adaptations. The aim of the present study was to investigate with the use of the variable neck chamber technique, the influence of the endogenous opioids on the carotid baroreflex control of blood pressure and heart rate at rest as well as during exercise. Ten normal volunteers exercised in the supine position up to 33% and 66% of their maximal exercise capacity and received, in a randomized double-blind cross-over protocol, either saline or naloxone (10 mg intravenously, followed by a continuous infusion of 10 mg.h-1). During exercise a progressive attenuation of the carotid baroreceptor reflex control of blood pressure and heart rate was noted. However, neither at rest nor during exercise, did opioid antagonism influence the carotid baroreceptor control of blood pressure and heart rate. Intra-arterial pressure and heart rate also remained unaffected. In contrast, both at rest and during exercise, naloxone administration produced a significant increase in the plasma concentration of cortisol. The latter suggests that in vivo the opioid receptors were effectively antagonized. In conclusion the present study confirms that opioids play only a minor role in cardiovascular homeostasis at rest. In addition, this study demonstrates that they are not involved in the cardiovascular adaptation to exercise, nor in the exercise-related attenuation of the carotid baroreceptor control of pressure and heart rate.

Biogenic amines and their metabolites in body fluids of normal, psychiatric and neurological subjects

The biogenic monoamines and their metabolites have been isolated, identified and quantified in human body fluids over the past forty years using a wide variety of chromatographic separation and detection techniques. This review summarizes the results of those studies on normal, psychiatric and neurological subjects. Tables of normal values and the methods used to obtain them should prove to be useful as a reference source for benchmark amine and metabolite concentrations and for successful analytical procedures for their chromatographic separation, detection and quantification. Summaries of the often contradictory results of the application of these methods to psychiatric and neurological problems are presented and may assist in the assessment of the validity of the results of experiments in this field. Finally, the individual, environmental and the methodological factors affecting the concentrations of the amines and their metabolites are discussed.

The psychopharmacologic and prolactin response after large doses of naloxone in man

Large doses of naloxone (150-300 mg), placebo, and morphine (15-30 mg) were given intramuscularly to human volunteers and compared using measures of subjective feeling states, physiological measures and discriminative features. Plasma prolactin responses after naloxone 210 mg and placebo were compared. The subjective measures and discriminative features of naloxone revealed that the drug is subtly psychoactive but the stimulus is vague and cannot be identified clearly as an opioid agonist or antagonist in nondependent opioid-using volunteers. The physiologic and prolactin responses closely resembled opiate agonist activity. We conclude that naloxone in this dose range may act as an opiate agonist in man.

Loss of the cortisol response to naltrexone in Alzheimer's disease

The administration of a single dose of the opiate antagonist naltrexone (NT) was accompanied by significant elevations in plasma cortisol in normal elderly subjects; in contrast, the cortisol response to NT was absent in individuals of comparable age with Alzheimer's disease (AD). The differential effect of AD on the cortisol response was not accompanied by a significant group difference in plasma prolactin in response to NT administration. Furthermore, this differential cortisol response to NT was not associated with any evident differences in age, sex ratio, plasma levels of naltrexone or its major metabolite beta-naltrexol, or with differences in measures of nonspecific stress, such as plasma free MHPG, pulse, or blood pressure, between the two groups. The absence of the well-characterized cortisol response to NT in AD, together with other reports of abnormal responses to other pharmacological challenges, suggests that neuroendocrine abnormalities might be an important concomitant and possibly a central contributor to the pathophysiology of Alzheimer's disease.

Mu-, delta-, kappa- and epsilon-opioid receptor modulation of the hypothalamic-pituitary-adrenocortical (HPA) axis: subchronic tolerance studies of endogenous opioid peptides

In opiate-naive rats, the endogenous opioid peptides, beta-endorphin, dynorphin(1-13) and Met-Enk-Arg-Phe (MEAP) and the synthetic enkephalin analogue D-Ala2-D-Leu5-Enk (DADLE) potently stimulated plasma corticosterone in a dose-dependent, naloxone reversible manner. To characterize their in vivo affinities, the effects of these peptides on plasma corticosterone release were tested in rats made tolerant to morphine, U50488H, DADLE/morphine or beta-endorphin. These cross-tolerance studies showed that dynorphin and MEAP exerted their action on plasma corticosterone release at kappa-opioid receptors. The action of DADLE occurred at delta-opioid receptors, while the action of beta-endorphin occurred principally at another receptor site. These results indicate that there is independent modulation of the hypothalamic-pituitary-adrenal axis by endogenous opioid peptides at mu-, delta- and kappa-opioid receptors. In addition there may be modulation by beta-endorphin at a separate site that we suggest could be a central epsilon-receptor site. This cross-tolerance paradigm, using a neuroendocrine model, provides in vivo evidence for the action of centrally active endogenous opioid peptides at multiple and independent opioid receptors.

Modulation of human neuroblastoma transplanted into nude mice by endogenous opioid systems

The role of endogenous opioid systems (endogenous opioids and opioid receptors) in human cancer was explored using an opioid antagonist paradigm and neuroblastoma cells (SK-N-MC) transplanted into nude mice. Mice inoculated with 2.5 X 10(6) neuroblastoma cells received daily injections of either 0.1 or 10 mg/kg naltrexone (=0.1 and 10 NTX groups) which blocked the opioid receptor for 6-8 hr/day or the entire 24 hr/day, respectively, or sterile water. The latency for appearance of a measurable tumor (5 mm diameter) in the 0.1 NTX group was 27% longer than controls (11 days), and the first death in this group occurred 33% later than controls (day 27). Mice inoculated with tumor cells in the 10 NTX group had an acceleration (18%) in the latency of tumor appearance and, 2 weeks after cell inoculation, 70% of the mice in this group had tumors, in contrast to 10% of the controls. At the termination of the experiment (day 45), only 33% of the 10 NTX group were alive, in contrast to 90% of the controls. Receptor binding assays using DAGO, DADLE, or EKC revealed specific saturable binding only for DADLE and EKC. NTX administration resulted in a 148-186% increase in density for both binding sites, but no changes in binding affinity. Measures of opioid levels showed that tumor tissue levels of both beta-endorphin and methionine-enkephalin were elevated 2.5 to 6.5 fold from control values in both NTX groups, whereas plasma beta-endorphin was subnormal by 4 to 6 fold. These results indicate that endogenous opioid systems regulate human neuro-oncogenesis, with opioids being active inhibitors of growth. Opioid antagonists up-regulate receptors and increase tissue levels of endogenous opioids and, under conditions in which the opioid antagonist is short-acting (e.g., 0.1 NTX), can have an exaggerated antitumor effect during the interval when the antagonist is no longer present.

Beta endorphin levels in CSF during methadone maintenance

Recent studies have shown that plasma beta endorphin levels of patients on methadone maintenance are comparable to controls. Furthermore, CSF levels of related peptides in methadone patients also do not differ from controls, although CSF levels of beta endorphin have not been specifically measured. In the current study we compared both CSF and plasma levels of beta endorphin in 11 patients on methadone maintenance for at least 10 months to levels in 13 controls getting spinal anesthesia for surgery. The CSF beta endorphin levels of the methadone maintained patients were significantly higher than the controls (52.3 vs 21.7 pg/ml), while plasma levels of beta endorphin (29.6 vs 31.1 pg/ml) and cortisol (13.8 vs 12.6 micro g/dl) [corrected] did not differ. Covarying for age differences between the samples, slightly increased the magnitude of this difference in CSF beta endorphin levels. Plasma levels of beta endorphin did not correlate with CSF levels, but did correlate with plasma levels of cortisol (r = 0.51, P less than 0.02). These findings supported previous studies of plasma beta endorphin levels. However, the dissociation of beta endorphin levels in plasma and CSF within this patient population was a new finding.

Plasma-free homovanillic acid: within- and across-day stability in children and adults with Tourette's syndrome

Within- and across-day stability of plasma-free homovanillic acid (pHVA) was assessed in children and adults with Tourette's syndrome. A diurnal fall in pHVA was observed in 13 of 15 subjects. There was a small but significant (p less than .0001) decrease (8%) in mean morning pHVA levels obtained just 20 minutes apart (8:30 A.M. and 8:50 A.M.). A substantial and significant (p less than .001) mean decrease in pHVA (25%) was observed when samples obtained between 8:00 and 8:30 A.M. were compared with samples obtained at 12:00 noon. Changes in pHVA levels observed during the afternoon (between 12:00 noon and 4:00 P.M.) were small, nondirectional, and nonsignificant. Repeated measurement of morning pHVA in the same individual after 24 or more hours revealed marked increases or decreases in many individuals, suggesting that morning pHVA is not a stable measure. The results of this and previous studies suggest that pHVA obtained at 12:00 noon or later in the day may be a more reliable measure of centrally produced HVA. Further studies are needed regarding the stability of pHVA over time.

Naloxone increases the response of growth hormone and prolactin to stimuli in obese humans

Opiates stimulate the growth hormone and prolactin responses to stimuli in non-obese humans. Obese patients, however, show lowered growth hormone and prolactin responses and raised beta-endorphin levels. We therefore investigated the effect of the opiate antagonist naloxone on the stimulated growth hormone and prolactin secretions in a controlled double-blind study in obese patients. All patients received 200 micrograms TRH and 0.5 g/kg b.w. arginine together with 2 mg of naloxone or placebo i.v. in a randomized sequence. The TRH- and arginine-induced increases in prolactin and growth hormone were significantly greater after administration of naloxone (p less than 0.05). Naloxone also produced a significant increase in ACTH, cortisol and beta-endorphin when compared with placebo. TSH, triiodothyronine, thyroxine, insulin, glucagon and blood glucose showed no significant differences between both days of the trial. The effect of naloxone on growth hormone and prolactin secretions in obese humans can thus be regarded as a partial normalization. We therefore conclude that the hypothalamic regulatory disturbance of growth hormone and prolactin secretions in the obese could be caused by raised opiate levels.

Sex-related naloxone influence on growth hormone-releasing hormone-induced growth hormone secretion in normal subjects

The effect of opiate-receptor antagonist naloxone on growth hormone (GH) release after growth hormone-releasing hormone (GHRH) 1-44 administration was investigated in ten normal men and 18 normal women during different phases of their menstrual cycle. Naloxone was infused at a rate of 1.6 mg/h in women and 1.6- and 3.2 mg/h in men, starting one hour before GHRH administration (50 micrograms iv as a bolus). On different day sessions, naloxone, GHRH, or saline were administered as controls. Naloxone infusion reduced the GHRH-induced GH release in normal women. The mean % inhibition of peak GH response was 83% during follicular phase, 46.5% during periovulatory phase, and 77.6% during luteal phase. On the contrary, in normal men, both doses of naloxone infusion were ineffective in blunting the GH response to GHRH. Our studies indicate that naloxone infusion was capable of inhibiting GH release induced by direct stimulation with GHRH in normal women, suggesting an opiate-antagonist action at the anterior pituitary level. The absence of such an effect in normal men strongly indicates a sex dependence of naloxone effects and suggests a role of the sexual steroid environment in opioid modulation of pituitary hormone secretion.

Multiple hormonal responses to morphine: relationship to diagnosis and dexamethasone suppression

Plasma cortisol, prolactin (PRL), growth hormone (GH), and thyroid stimulating hormone (TSH) responses to intravenous morphine (0.1 mg/kg body weight) were investigated in five healthy women and 22 female psychiatric inpatients (eight with major depression, 12 with schizophrenia and two with personality disorders) during a 120 min period. The results were also related to a subsequent dexamethasone suppression test (DST). Morphine caused a strong and progressive decline in plasma cortisol which was uniform in controls, depressed, and nondepressed patients. DST nonsuppressors had significantly higher cortisol levels during the entire period, but the same response to morphine. Morphine strongly stimulated PRL secretion, which was found to be significantly smaller in patients than in controls, but no difference was seen between depressed and nondepressed subjects. GH and TSH showed only minor and variable changes after morphine, with no overall significant differences. The data in this study do not support the assumption of a major alteration in opiate receptor responsivity either in depression or in DST nonsuppressor patients insofar as the regulation of the adrenal, thyroid, GH and PRL hormone secretion is concerned.

Cardiovascular and endocrine effects of naloxone compared in normotensive and hypertensive patients

Naloxone, a competitive antagonist of opioid receptors, and placebo (dextrose 5% in water (D5W) were administered on separate days to healthy normotensive (NT) male volunteers and to male patients with essential hypertension (HT). A single-blind, placebo-controlled, cross-over design was employed. Increasing doses of naloxone (0.4, 1.2, 3.6, 10.8, 32.4, 97.2 mg) were given every 30 min as slow i.v. boluses. On a separate day, i.v. boluses of D5W were given according to a similar protocol. Naloxone failed to significantly modify systolic and diastolic blood pressure (BP), heart rate (HR), respiratory rate, oral temperature or plasma catecholamines. No adverse reactions or behavioral effects were seen with naloxone. Naloxone produced a dose-dependent increase in plasma cortisol, whereas plasma cortisol showed a gradual decline on the placebo day (circadian variation). HT and NT showed similar maximal increases in plasma cortisol. Hypertensives responded to lower doses of naloxone with greater increases in plasma cortisol. The results were significantly different only if corrected by using the baseline values obtained on the placebo day. The study suggests that in awake, resting men, endogenous opioids play no role in regulating BP, HR, respiration, temperature or the activity of the sympathetic nervous system. It also suggests that the sustained elevation of BP in HT is not due to endogenous opioid substances. However, endogenous opioid substances produce a tonic inhibitory effect on the release of cortisol. This tonic inhibition seems to be greater in hypertensives than in normotensives.

A preliminary study of beta endorphin during chronic naltrexone maintenance treatment in ex-opiate addicts

Because opioid antagonists acutely produce rises in serum beta endorphin, we studied beta endorphin levels in 21 former opiate addicts chronically taking naltrexone. The mean AM (19.5 pg/ml) beta endorphin level was higher than the AM mean for 39 normals under 40 years old (12.1 pg/ml) (t = 3.2, p less than 0.001); the mean PM level for the naltrexone treated patients was 13.6 pg/ml. Four patients had beta endorphin levels more than 2 S.D. above the mean for the normals (greater than 26.4 pg/ml), and six others had relatively elevated PM levels. Thus, 47% (10/21) had abnormal patterns of beta endorphin levels. We had previously reported abnormally high cortisol levels in these patients, and AM cortisol correlated with AM beta endorphin levels (r = 0.7, p less than 0.001). We concluded that sustained beta endorphin elevations may occur during chronic naltrexone treatment.

Opiate receptor sensitivity in depressed patients before and after clomipramine treatment

To measure opiate receptor sensitivity, the effects of naloxone on beta-endorphin and cortisol serum levels were determined before and after 3 weeks of clomipramine treatment (75 mg/day i.v.) in 12 patients with major depressive disorder. The opiate antagonist significantly increased both hormonal levels. The only significant endocrine differences between pre- and post-treatment were basal and maximal cortisol levels, which were elevated before antidepressant therapy. The rise in the cortisol or beta-endorphin serum level after naloxone injection was not affected by clomipramine treatment. There was no significant relationship between depression score and basal or stimulated endocrine variables. These data do not indicate a distinct effect of antidepressants on opiate receptor sensitivity.

[Factors interfering with the dexamethasone suppression test]

The interpretation of the dexamethasone suppression test in endocrinology and psychiatry depends on several variables. False-positive results can be caused by stress, weight loss, alcohol withdrawal, treatment with diphenylhydantoin, phenobarbital, rifampicin, carbamazepine and lithium. Therapy with spironolactone, naloxone, alpha 1-mimetic agents and estrogen can be responsible for an increase in plasma-cortisol concentration. False-negative results are seen in patients with liver disease and can also result from therapy with benzodiazepines at high dosages, indomethacin and possibly methadone and ketoconazole.

Endogenous opioid regulation of hypothalamo-pituitary-adrenal axis activity in schizophrenia

We utilized a naloxone challenge strategy to investigate the functioning of the endogenous opioid system (EOS) in schizophrenia. Patients with schizophrenia, who were on neuroleptic medication or drug-free, demonstrated a significantly larger serum cortisol response to opioid blockade by naloxone than did age- and sex-matched normal controls. Patients, but not normal controls, also demonstrated an inverse relationship between baseline cortisol and the magnitude of the response. This enhanced cortisol response is consistent with tonic hyperactivity of the EOS in schizophrenia.

Brief debrisoquin administration to assess central dopaminergic function in children

Central dopaminergic (DA) function in children was assessed by monitoring plasma-free homovanillic acid (pHVA) levels after brief (18 hour) administration with debrisoquin sulfate, a peripherally active antihypertensive agent that blocks peripheral, but not central, HVA production. Brief debrisoquin administration resulted in marked reductions in pHVA in each of six patients studied. In five of the six patients, post-debrisoquin pHVA levels remained relatively stable over the six-hour period of observation. No significant cardiovascular or behavioral side effects of debrisoquin were observed. The brief debrisoquin administration method appears to be a safe, simple, and potentially valid peripheral technique for evaluating aspects of central dopaminergic function in children with neuropsychiatric disorders. Additional work is needed to further establish this method's validity and reliability.

Assessment of central dopaminergic function using plasma-free homovanillic acid after debrisoquin administration

Central dopaminergic (DA) function in children and adults was assessed by monitoring plasma-free levels of the dopamine metabolite homovanillic acid (pHVA) before and after a single oral dose and chronic oral administration of debrisoquin. Debrisoquin inhibits peripheral metabolism of dopamine to HVA and does not cross the blood-brain barrier. By reducing peripheral formation of HVA through the use of debrisoquin, the remaining HVA in plasma more accurately reflects central DA activity. Debrisoquin administration resulted in marked reductions of pHVA in each of 12 patients studied. Eleven of the 12 subjects tolerated debrisoquin without physical or behavioral side effects. The debrisoquin administration method appears to be a safe and potentially valid technique for evaluating aspects of central dopaminergic function in children and adults.

Multiple, single-dose naltrexone administrations fail to effect overall cognitive functioning and plasma cortisol in individuals with probable Alzheimer's disease

A double-blind placebo-controlled study was conducted in 10 individuals with probable Alzheimer's disease to assess the effects of varying doses of Naltrexone (0, 25, 50 and 100 mg) on cognitive functioning and on plasma cortisol. Each individual participated in four separate sessions at least three days apart. Naltrexone was found to improve performance in only one of the six psychometric tasks employed (Token Test). However, enhancement of Token Test performance was limited to the 25 mg Naltrexone dose and was mainly the result of an improvement on the part of the two most severely impaired patients. In contrast to the previous reports of elevations of plasma cortisol following administration of opiate antagonists to younger, non-demented subjects, Naltrexone administration failed to produce any significant increase in plasma cortisol in Alzheimer's patients.

Hormonal effects of high dose naloxone in humans

Utilizing a double-blind crossover design, the hormonal effects of high dose, 2 mg/kg, were compared to low dose, 0.4 mg (approx. 5 micrograms/kg), naloxone administration in physically healthy humans. A significant naloxone dose effect on plasma cortisol levels was found (p less than 0.001), but no significant effect on plasma or serum levels of prolactin, follicle stimulating hormone, luteinizing hormone, norepinephrine or epinephrine. These results confirm involvement of the endogenous opioid system (EOS) in the tonic regulation of the hypothalamicpituitary-adrenal axis, but fail to find evidence of EOS involvement in the regulation of adrenal medullary function or the gonadotrophic axis in man. The results are however consistent with a continuing action of naloxone as an EOS antagonist even at high doses in man.

Neuroendocrinology of opioid peptides and their role in the control of gonadotropin and prolactin secretion

Substantial evidence now exists to indicate that the endogenous hypothalamic opioidergic mechanism(s) represents one of the important controlling systems for release of gonadotropin-releasing hormone. Modulations of frequency and amplitude of the secretory activity of gonadotropin-releasing hormone appears to be mediated through an inhibitory action of endogenous opioids, and the functional coupling of the opioidergic and gonadotropin-releasing hormone systems is an ovarian steroid-dependent event. There is also evidence to implicate suprahypothalamic mechanism(s) that enhance endogenous opioid inhibition of secretion of gonadotropin-releasing hormone. Although exogenous opioid peptides and their synthetic analogs consistently induce the secretion of prolactin, blockade of opioid receptors in humans by naloxone failed to elicit a decrement in the levels of prolactin under a variety of conditions. On the contrary, naloxone induced a remarkable increment in the secretion of prolactin via an increased frequency of pulsatile release which is synchronized with pulses of luteinizing hormone. These observations suggest that a common neuroendocrine mechanism is involved in the opioidergic control of the secretion of both luteinizing hormone and prolactin in women.

d-Amphetamine raises cortisol levels in schizophrenic patients with and without chronic naltrexone pretreatment

Five drug-free schizophrenic patients received an infusion of 20 mg d-amphetamine and placebo on separate days in a pilot study. Plasma cortisol levels rose significantly at 1 and 2 hours after d-amphetamine compared to following placebo. A repeat infusion of d-amphetamine during naltrexone treatment led to a similar increase in cortisol concentrations.