Effects of cocaine on excitation-contraction coupling of aortic smooth muscle from the ferret

Ephedrine and cocaine cause developmental neurotoxicity and abnormal behavior in zebrafish

Ephedrine (EPH) and cocaine (COC) are illegal stimulant drugs, and have been frequently detected in aquatic environments. EPH and COC have negative effects on the nervous system and cause abnormal behaviors in mammals and fish at high concentrations, but their mechanisms of neurotoxicity remain unclear in larvae fish at low concentrations. To address this issue, zebrafish embryos were exposed to EPH and COC for 14 days post-fertilization (dpf) at 10, 100, and 1000 ng L-1. The bioaccumulation, development, behavior, cell neurotransmitter levels and apoptosis were detected to investigate the developmental neurotoxicity (DNT) of EPH and COC. The results showed that EPH decreased heart rate, while COC increased heart rate. EPH caused cell apoptosis in the brain by AO staining. In addition, behavior analysis indicated that EPH and COC affected spontaneous movement, touch-response, swimming activity and anxiety-like behaviors. EPH and COC altered the levels of the neurotransmitters dopamine (DA) and γ-aminobutyric acid (GABA) with changes of the transcription of genes related to the DA and GABA pathways. These findings indicated that EPH and COC had noticeable DNT in the early stage of zebrafish at environmentally relevant concentrations.

Neurochemical and Cardiovascular Effects of 4-Chloro Ring-Substituted Synthetic Cathinones in Rats

Synthetic cathinones are a class of new psychoactive substances that display psychomotor stimulant properties, and novel cathinone analogs continue to emerge in illicit drug markets worldwide. The aim of the present study was to characterize the pharmacology of 4-chloro ring-substituted cathinones that are appearing in illicit drug markets compared with the effects of 4-methylmethcathinone (mephedrone). Synaptosomes were prepared from rat caudate for dopamine transporter (DAT) assays or from whole brain minus caudate and cerebellum for norepinephrine transporter (NET) and serotonin transporter (SERT) assays. Findings from transporter uptake inhibition and release assays showed that mephedrone and 4-chloromethcathinone (4-CMC) function as substrates at DAT, NET, and SERT, with similar potency at all three transporters. In contrast, 4-chloro-α-pyrrolidinopropiophenone (4-CαPPP) was an uptake inhibitor at DAT and NET, with similar potency at each site, but had little activity at SERT. 4-Chloroethcathinone (4-CEC) was a low-potency uptake inhibitor at DAT and NET but a substrate at SERT. In rats implanted with telemetry transmitters, mephedrone and 4-CMC increased blood pressure, heart rate, and locomotor activity to a similar extent. 4-CEC and 4-CαPPP were less potent at increasing blood pressure and had modest stimulatory effects on heart rate and activity. 4-CMC also transiently decreased temperature at the highest dose tested. All three 4-chloro ring-substituted cathinones are biologically active, but only 4-CMC has potency comparable to mephedrone. Collectively, our findings suggest that 4-CMC and other 4-chloro cathinones may have abuse potential and adverse effects in humans that are analogous to those associated with mephedrone. SIGNIFICANCE STATEMENT: The 4-chloro ring-substituted cathinones all produced significant cardiovascular stimulation, with 4-chloromethcathinone (4-CMC) showing potency similar to mephedrone. All of the drugs are likely to be abused given their effects at the dopamine transporter, particularly 4-CMC.

MicroRNA-423-5p Mediates Cocaine-Induced Smooth Muscle Cell Contraction by Targeting Cacna2d2

Cocaine abuse increases the risk of atherosclerotic cardiovascular disease (CVD) and causes acute coronary syndromes (ACS) and hypertension (HTN). Significant research has explored the role of the sympathetic nervous system mediating the cocaine effects on the cardiovascular (CV) system. However, the response of the sympathetic nervous system alone is insufficient to completely account for the CV consequences seen in cocaine users. In this study, we examined the role of microRNAs (miRNAs) in mediating the effect of cocaine on the CV system. MiRNAs regulate many important biological processes and have been associated with both response to cocaine and CV disease development. Multiple miRNAs have altered expression in the CV system (CVS) upon cocaine exposure. To understand the molecular mechanisms underlying the cocaine response in the CV system, we studied the role of miRNA-423-5p and its target Cacna2d2 in the regulation of intracellular calcium concentration and SMC contractility, a critical factor in the modulation of blood pressure (BP). We used in vivo models to evaluate BP and aortic stiffness. In vitro, cocaine treatment decreased miR-423-5p expression and increased Cacna2d2 expression, which led to elevated intracellular calcium concentrations and increased SMC contractility. Overexpression of miR-423-5p, silencing of its target Cacna2d2, and treatment with a calcium channel blocker reversed the elevated SMC contractility caused by cocaine. In contrast, suppression of miR-423-5p increased the intracellular calcium concentration and SMC contractibility. In vivo, smooth muscle-specific overexpression of miR-423-5p ameliorated the increase in BP and aortic stiffness associated with cocaine use. Thus, miR-423-5p regulates SMC contraction by modulating Cacna2d2 expression increasing intracellular calcium concentrations. Modulation of the miR-423-5p-Cacna2d2-Calcium transport pathway may represent a novel therapeutic strategy to improve cocaine-induced HTN and aortic stiffness.

Short- and Long-Term Effects of Cocaine on Enteric Neuronal Functions

Cocaine is one of the most consumed illegal drugs among (young) adults in the European Union and it exerts various acute and chronic negative effects on psychical and physical health. The central mechanism through which cocaine initially leads to improved performance, followed by addictive behavior, has already been intensively studied and includes effects on the homeostasis of the neurotransmitters dopamine, partly mediated via nicotinic acetylcholine receptors, and serotonin. However, effects on the peripheral nervous system, including the enteric nervous system, are much less understood, though a correlation between cocaine consumption and gastrointestinal symptoms has been reported. The aim of the present study was to gain more information on the effects of cocaine on enteric neuronal functions and the underlying mechanisms. For this purpose, functional experiments using an organ bath, Ussing chamber and neuroimaging techniques were conducted on gastrointestinal tissues from guinea pigs. Key results obtained are that cocaine (1) exhibits a stimulating, non-neuronal effect on gastric antrum motility, (2) acutely (but not chronically) diminishes responses of primary cultured enteric neurons to nicotinic and serotonergic stimulation and (3) reversibly attenuates neuronal-mediated intestinal mucosal secretion. It can be concluded that cocaine, among its central effects, also alters enteric neuronal functions, providing potential explanations for the coexistence of cocaine abuse and gastrointestinal complaints.

Impact of maternal substance use on offspring's cardiovascular health

Substance use (SU) during pregnancy is on the rise, posing significant risks to the developing fetus. The adverse impact of maternal alcohol and nicotine use during the perinatal period on offspring health has been well established, including their associations with adverse cardiovascular health in offspring. However, limited studies examine the impact of other well-known SU utilized during pregnancy on offspring's cardiovascular health. This review summarizes the proposed mechanism of action of four commonly utilized substances: cocaine, marijuana, methamphetamine, and opioids, and their cardiovascular impact. Furthermore, we will review the current understanding of the adverse impact of substance use during pregnancy on offspring's cardiovascular system based on existing studies. This review will also highlight possible molecular mechanisms underlying the in-utero adverse programming of offspring's cardiovascular system secondary to SU in pregnancy and address the gaps in current understanding of how SU adversely impacts the developing cardiovascular system of offspring in utero.

Early Onset Cardiovascular Disease from Cocaine, Amphetamines, Alcohol, and Marijuana

Cardiovascular disease (CVD), a disease typically associated with aging and the definitive leading cause of death worldwide, now threatens the young and middle-aged populations. Recreational abuse of alcohol, marijuana, cocaine and amphetamine-type stimulants has been an escalating public health problem for decades, but now use of these substances has become a significant contributor to early onset CVD. While this remains a global phenomenon, the epicenter of substance abuse is rooted in North America where it has been exacerbated by the COVID-19 pandemic. For the first time in history, the United States (US) crossed 100,000 overdose-related deaths in a calendar year. Sadly, Canada's recreational drug abuse problem closely mirrors that of the US. This is indicative of the larger public health crisis unfolding, as we now know that these substances are cardiotoxic and are contributing to the rising levels of premature chronic CVD, including hypertension, arrhythmias, heart failure, stroke, myocardial infarction, arterial dissection, sudden cardiac death and early mortality.

An Increase in Peripheral Temperature following Cocaine Administration Is Mediated through Activation of Dopamine D2 Receptor in Rats

Drug addiction has become a worldwide problem, affecting millions of people across the globe. While the majority of mechanistic studies on drug addiction have been focused on the central nervous system, including the mesolimbic dopamine system, the peripheral actions of drugs of abuse remain largely unknown. Our preliminary study found that the systemic injection of cocaine increased peripheral skin temperature. This led us to our present study, which investigated the mechanisms underlying the increase in peripheral temperature following cocaine injection. Male Sprague Dawley rats were anesthetized with pentobarbital sodium, and peripheral skin temperature measurements were taken using a thermocouple needle microprobe and an infrared thermal camera. Cocaine injection caused an acute rise in peripheral body temperature, but not core body temperature, about 10 min after injection, and the temperature increases were occluded by systemic injection of dopamine D2 receptor antagonist L741,626, but not D1 receptor antagonist SCH23390. In addition, systemic administration of bromocriptine, a dopamine D2 receptor agonist, significantly increased peripheral temperature. Infrared thermal imaging showed that the thermal increases following cocaine injection were predominantly in the distal areas of the forelimbs and hindlimbs, relative to core body temperature. Treatment with cocaine or bromocriptine decreased the size of skin blood vessels without affecting the expression of dopamine D2 receptors. These results suggest that increased peripheral temperature in skin following cocaine injection is associated with the activation of the dopamine D2 receptor.

Drugs of Abuse and Heart Failure

Substance use is common among those with heart failure (HF) and is associated with worse clinical outcomes. Alcohol, tobacco, cannabis, and cocaine are commonly abused substances that can contribute to the development and worsening of HF. Heavy alcohol consumption can lead to dilated cardiomyopathy, whereas moderate intake may decrease incident HF. Tobacco increases the risk of HF through coronary artery disease and coronary artery disease-independent mechanisms. Continued smoking worsens outcomes for those with HF and cessation is associated with an improved risk of major adverse cardiac events. Cannabis has complex interactions on the cardiovascular system depending on the method of consumption, amount consumed, and content of cannabinoids. Delta-9-tetrahydrocannabinol can increase sympathetic tone, cause vascular dysfunction, and may increase the risk of myocardial infarction. Cannabidiol is cardioprotective in preclinical studies and is a potential therapeutic target. Cocaine increases sympathetic tone and is a potent proarrhythmogenic agent. It increases the risk of myocardial infarction and can also lead to a dilated cardiomyopathy. The use of beta-blockers in those with HF and cocaine use is likely safe and effective. Future studies are needed to further elucidate the impact of these substances both on the development of HF and their effects on those who have HF.

Cocaine-Related Aortic Dissection: what do we know?

Introduction

Cocaine use is known to be associated with an increased risk for vascular diseases. It is likely to trigger or increase the risk for an aortic dissection. We conducted an analysis of 45 cases of cocaine-related aortic dissection to further characterize the clinical features and outcomes of this patient cohort.

Methods

Our study cohort of 45 patients consisted of 11 cases from our institutional database and 34 published case reports.

Results

The observed cases of acute aortic dissection related to cocaine use showed a high proportion of young (41.3±8.67 years) and male (88.9%) patients. Most of the cases (75%) were classified as Stanford type A. Also, in 75% of the cases, cocaine use was prevalent for more than one year. Median time from last cocaine use to onset of symptoms was one hour. In-hospital mortality was 21.4%, while additional 11.9% of the cases died before arriving at the hospital.

Conclusion

Acute aortic dissection related to cocaine use occurs in predominantly young male patients and has a dismal outcome when compared to all comer series.

Hemodynamic and neuronal responses to cocaine differ in awake versus anesthetized animals: Optical brain imaging study

Cocaine is a highly addictive drug with complex pharmacological effects. Most preclinical imaging studies investigating the effects of cocaine in the brain have been performed under anesthesia, which confounds findings. To tackle this problem, we used optical imaging to compare the effects of cocaine in the awake versus the anesthetized states. For this purpose, we customized an air floating mobile cage to fit the multi-wavelength spectral and laser speckle optical imaging system and implanted a multi-layer cranial window over the mouse somatosensory cortex. Results showed significant differences in neuronal activity and hemodynamics at baseline and in response to cocaine between the awake and the anesthetized states (isoflurane anesthesia). Specifically, 1) at baseline isoflurane dilated cerebral vessels, increased cerebral blood flow and depressed neuronal Ca²⁺ activity compared to the awake state; 2) acute cocaine (1 mg/kg iv) vasoconstricted blood vessels (arteries and veins) and decreased cerebral blood flow and oxygenated hemoglobin in the anesthetized state but not in the awake condition; 3) cocaine increased the accumulation of mean intracellular Ca²⁺ in neurons in the anesthetized state but not in the awake condition; and 4) in the awake state acute cocaine increased neuronal activities (increased the frequency of Ca²⁺ transients) and increased neuronal synchronization. We also corroborated that in the awake state cocaine also disrupted neurovascular coupling. These findings indicate that both vascular and neuronal responses to cocaine are influenced by isoflurane anesthesia, which highlights the importance of imaging awake animals when studying the effects of cocaine or other drugs in the brain.

Cocaine Exposure Increases Blood Pressure and Aortic Stiffness via the miR-30c-5p-Malic Enzyme 1-Reactive Oxygen Species Pathway

Cocaine abuse increases the risk of cardiovascular mortality and morbidity; however, the underlying molecular mechanisms remain elusive. By using a mouse model for cocaine abuse/use, we found that repeated cocaine injection led to increased blood pressure and aortic stiffness in mice associated with elevated levels of reactive oxygen species (ROS) in the aortas, a phenomenon similar to that observed in hypertensive humans. This ROS elevation was correlated with downregulation of Me1 (malic enzyme 1), an important redox molecule that counteracts ROS generation, and upregulation of microRNA (miR)-30c-5p that targets Me1 expression by directly binding to its 3'UTR (untranslated region). Remarkably, lentivirus-mediated overexpression of miR-30c-5p in aortic smooth muscle cells recapitulated the effect of cocaine on Me1 suppression, which in turn led to ROS elevation. Moreover, in vivo silencing of miR-30c-5p in smooth muscle cells resulted in Me1 upregulation, ROS reduction, and significantly suppressed cocaine-induced increases in blood pressure and aortic stiffness-a similar effect to that produced by treatment with the antioxidant N-acetyl cysteine. Discovery of this novel cocaine-↑miR-30c-5p-↓Me1-↑ROS pathway provides a potential new therapeutic avenue for treatment of cocaine abuse-related cardiovascular disease.

The Cardiovascular Effects of Cocaine

Cocaine is the leading cause for drug-abuse-related visits to emergency departments, most of which are due to cardiovascular complaints. Through its diverse pathophysiological mechanisms, cocaine exerts various adverse effects on the cardiovascular system, many times with grave results. Described here are the varied cardiovascular effects of cocaine, areas of controversy, and therapeutic options.

Vascular disease in cocaine addiction

Cocaine, a powerful vasoconstrictor, induces immune responses including cytokine elevations. Chronic cocaine use is associated with functional brain impairments potentially mediated by vascular pathology. Although the Crack-Cocaine epidemic has declined, its vascular consequences are increasingly becoming evident among individuals with cocaine use disorder of that period, now aging. Paradoxically, during the period when prevention efforts could make a difference, this population receives psychosocial treatment at best. We review major postmortem and in vitro studies documenting cocaine-induced vascular toxicity. PubMed and Academic Search Complete were used with relevant terms. Findings consist of the major mechanisms of cocaine-induced vasoconstriction, endothelial dysfunction, and accelerated atherosclerosis, emphasizing acute, chronic, and secondary effects of cocaine. The etiology underlying cocaine's acute and chronic vascular effects is multifactorial, spanning hypertension, impaired homeostasis and platelet function, thrombosis, thromboembolism, and alterations in blood flow. Early detection of vascular disease in cocaine addiction by multimodality imaging is discussed. Treatment may be similar to indications in patients with traditional risk-factors, with few exceptions such as enhanced supportive care and use of benzodiazepines and phentolamine for sedation, and avoiding β-blockers. Given the vascular toxicity cocaine induces, further compounded by smoking and alcohol comorbidity, and interacting with aging of the crack generation, there is a public health imperative to identify pre-symptomatic markers of vascular impairments in cocaine addiction and employ preventive treatment to reduce silent disease progression.

The effects of cocaine on heart rate and electrocardiogram in zebrafish (Danio rerio)

Zebrafish (Danio rerio) have been used as a model organism to explore the genetic basis for responsiveness to addictive drugs like cocaine. However, very little is known about how the physiological response to cocaine is mediated in zebrafish. In the present study electrocardiograms (ECGs) were recorded from adult zebrafish treated with cocaine. Treatment with cocaine resulted in a bell-shaped dose response curve with a maximal change in heart rate seen using 5mg/L cocaine. Higher doses resulted in a higher percentage of fish showing bradycardia. The cocaine-induced tachycardia was blocked by co-treatment with propranolol, a β-adrenergic antagonist, but potentiated by co-treatment with phentolamine, an α-adrenergic antagonist. Co-treatment with atropine, a classic cholinergic antagonist, had no effect on cocaine-induced tachycardia. Cocaine treatment of adult fish changed the ECG of treated fish, inducing a dose-dependent increase in QT interval after adjusting for heart rate (QTc), while not affecting the PR or QRS intervals. The acute effects of cocaine on heart rate were examined in 5-day old embryos to see if zebrafish might serve as a suitable model organism to study possible links of embryonic physiological response to subsequent adult behavioral response to the drug. Cocaine treatment of 5-day old zebrafish embryos also resulted in a bell-shaped dose response curve, with maximal tachycardia achieved with 10mg/L. The response in embryonic fish was thus comparable to that in adults and raises the possibility that the effects of embryonic exposure to cocaine on the developing cardiovascular system can be effectively modeled in zebrafish.

Cocaine-induced relaxation of isolated rat aortic rings and mechanisms of action: possible relation to cocaine-induced aortic dissection and hypotension

Cocaine HCl is well known for its toxic effects on the cardiovascular system, but little is known about its effects on different regional blood vessels. We designed experiments to determine if cocaine HCl could influence the tension of isolated aortic rings, i.e., induce contraction or relaxation. Surprisingly, cocaine HCl (1 x 10(-5) to 6 x 10(-3) M) relaxed isolated aortic rings precontracted by phenylephrine in a concentration-dependent manner. No significant differences were found between intact or denuded isolated aortic rings (P>0.05). The maximal % relaxations of intact vs. denuded isolated aortic rings were 108.9+/-24.3% vs. 99.5+/-8.3% (P>0.05). Cocaine HCl, 2 x 10(-3) M, was found to inhibit contractions by phenylephrine; EC50s were increased (P<0.01) and Emax's were decreased (51.3+/-16.4% vs. 89.8+/-10.6%, P<0.01). A variety of amine antagonists could not inhibit the relaxant effects of cocaine HCl (P>0.05). The cyclooxygenase-1 inhibitor, indomethacin, also failed to inhibit relaxations induced by cocaine HCl (P>0.05). Neither L-arginine, NG-monomethyl-L-arginine (L-NMMA), nor methylene blue could inhibit the relaxations induced by cocaine HCl (P>0.05), suggesting cocaine HCl does not relax isolated aortic rings by inducing the synthesis or release of nitric oxide (NO) or prostanoids from either endothelial or vascular muscle cells. Inhibitors of cAMP, cGMP and protein kinase G (PKG) also failed to inhibit cocaine-induced relaxations. Cocaine HCl (1 x 10(-5) to 6 x 10(-3) M) could also relax isolated aortic rings precontracted by phenylephrine in high K+ depolarizing buffer. Surprisingly, calyculin A, an inhibitor of myosin light chain (MLC) phosphatase, inhibited cocaine-induced relaxations in a concentration-dependent manner, suggesting the probable importance of cocaine-induced MLC phosphatase activation in rat aortic smooth muscle cells. It was also found that cocaine HCl could dose-dependently inhibit Ca2+-induced contractions of isolated aortic rings in high K+-Ca2+-free buffer, suggesting that cocaine HCl may inhibit Ca2+ influx and/or intracellular release.

Cardiovascular manifestations of substance abuse part 1: cocaine

Substance abuse with cocaine is associated with multiple cardiovascular conditions, including myocardial infarction, dissection, left ventricular hypertrophy, arrhythmias, sudden death, and cardiomyopathy. Cocaine has effects to potentiate the physiologic actions of catecholamines and has direct effects on voltage-dependent sodium ion channels related to local anesthetic properties. The effects of cocaine can be augmented with concomitant alcohol consumption. Acute myocardial ischemia caused by cocaine may be related to in situ thromboisis and/or coronary vasospasm. Treatment strategies for cocaine-induced myocardial infarction would include antiplatelet therapy, thrombolysis, and vasodilators (eg, nitrates, nifedipine). Beta-adrenergic blockers should not be used unless concomitant vasodilator therapy is given.

Percutaneous interventions in patients with cocaine-associated myocardial infarction: a case series and review

Cocaine-associated myocardial infarction (CAMI) is a well-reported entity. Most previous reports on CAMI have been limited to conservative care utilizing benzodiazepines, aspirin, nitroglycerin, calcium channel blockers, and thrombolytics. Current guidelines on CAMI advocate immediate use of angiography and angioplasty if available rather than routine administration of thrombolytics. However, based on literature search from 1966 to 2001 (using keywords "cocaine," "myocardial infarction," and "angioplasty"), there have been only two case reports of percutaneous coronary intervention (PCI) in patients with cocaine-associated myocardial infarction. Both were notable for complications either during or immediately after the procedure. We report a series of 10 patients with cocaine-associated myocardial infarction who were treated with percutaneous interventions, which included angioplasty, stenting, and AngioJet mechanical extraction of thrombus. Despite the different arteriopathic process involved, our findings suggest that PCI can be performed safely and with a high degree of procedural success in patients with CAMI.

Effect of endogenous catecholamine on myocardial stunning in a simulated ischemia model

During ischemia, large amounts of catecholamine are released to the myocardium from the sympathetic nerve endings in the heart. It has not been clearly shown whether the released catecholamine has detrimental or beneficial effects on postischemic myocardial contractile function. The aim of the present study was to investigate the effect of endogenous catecholamine released during ischemia on myocardial contractile function, using ferret papillary muscles in a stimulated ischemia model. Papillary muscles were excised and mounted in organ baths containing oxygenated physiological salt solution at 37 degrees C. In order to eliminate the effect of endogenous catecholamine, a subset of animals was reserpinized for 2 days prior to the experiments. Muscles were stabilized for 1 h, and stretched to the length at which maximal isometric tension developed. Ischemia was simulated by changing the solution to liquid fluorocarbon bubbled with 95% N2 and 5% CO2. After 20 min of ischemia, the bathing medium was replaced with oxygenated physiological salt solution and developed tension was measured for 60 min. Pharmacologic agents with specific effects on myocardial autonomic pathways were used to investigate the cellular mechanisms of the observed effects. Tension recovery of reserpinized muscles was significantly better than control muscles (65.5 +/- 2.8% vs. 54.9 +/- 5.0%, P < 0.01). Exogenously administered beta-adrenergic antagonists did not attenuate stunning in control muscles; whereas forskolin and carbachol exacerbated stunning. These results indicate that catecholamine released during ischemia exacerbates myocardial stunning and overrides the effect of clinically relevant concentrations of beta-adrenergic antagonists, which may limit their ability to protect myocardium from acute ischemic insult. The effect of endogenous catecholamine was simulated by forskolin, but not attenuated by carbachol, which suggests that changes in the contractile apparatus activated by excess cyclic AMP were relevant to the mechanical dysfunction that developed.

Cardiotoxic mechanisms and interrelationships of cocaine: including a single case depicting several of these mechanisms

The underlying mechanisms of myocardial infarction as a result of cocaine abuse appear to be multifactorial. The various cardiotoxic mechanisms and interrelationships of cocaine are fully reviewed, and a chart has been reconstructed to give the reader a clearer understanding of them. Moreover, an unusual case of a 29-year-old male cocaine abuser is presented because it illustrates many of the reported cardiotoxic effects, all of which are present in the same individual.

Cocaine augments contractility of the pregnant human uterus by both adrenergic and nonadrenergic mechanisms

OBJECTIVE

Our purpose was to evaluate the mechanisms of cocaine's effect on both spontaneous and agonist-induced contractility of pregnant human myometrium.

STUDY DESIGN

Myometrium was obtained from 42 women at term who were undergoing cesarean section. Myometrial strips were suspended in contraction baths and isometric contractions were measured. Tissue was exposed to various combinations of cocaine, prazosin, desipramine, benzoylecgonine, and procaine. Spontaneous contractility and the contractile responses to increasing concentrations of methoxamine and oxytocin were measured and compared.

RESULTS

Cocaine increased spontaneous myometrial contractility by more than threefold. Prazosin, an alpha-adrenergic antagonist, blocked this effect only for the first 35 minutes of exposure. The cumulative concentration-response to the alpha-adrenergic agonist methoxamine was increased by cocaine in terms of both sensitivity and maximal response. The maximal response to oxytocin, but not the sensitivity, was increased by cocaine by an effect that could not be blocked by prazosin.

CONCLUSION

Cocaine augments spontaneous and agonist-induced contractility of pregnant human myometrium by mechanisms that appear to be both alpha-adrenergic and nonadrenergic in nature.

Biphasic inotropic effects of methamphetamine and methylphenidate on ferret papillary muscles

Methamphetamine and methylphenidate are structurally related agents that have direct negative inotropic (NIEs) and indirect positive inotropic effects (PIEs) in cardiac tissues. This study was designed to determine and compare cellular mechanisms of the NIEs of methamphetamine and methylphenidate by using a mammalian animal model. Isometric tension was measured in ferret papillary muscles in physiologic salt solution. A subset of muscles was loaded with the bioluminescent calcium indicator, aequorin. Further, to investigate the NIE of methamphetamine, the dose-response relations to isoproterenol, histamine, and calcium were measured with or without methamphetamine (2 x 10(-4) M), after adrenergic neuronal blockade with reserpine. Both methamphetamine and methylphenidate had direct NIEs at higher doses (>10(-4) M). A shift in the slope of the isoproterenol dose-response curve suggested involvement of the beta-adrenoceptor pathways. The direct NIE of methylphenidate was more prominent. Our results suggest that the negative inotropic effects of methamphetamine and methylphenidate may be important with clinically used and abused concentrations of these drugs and may be difficult to reverse with beta-adrenergic inotropic agents in cases of toxicity.

Cocaine-induced myocardial ischemia and infarction: pathophysiology, recognition, and management

As cocaine abuse has become widespread, it has been associated with various cardiovascular complications, including angina pectoris, myocardial infarction, and sudden cardiac death. Cocaine's principal effects on the cardiovascular system are mediated via alpha-adrenergic stimulation and include (1) an increase in the determinants of myocardial oxygen demand (heart rate and systemic arterial pressure), and (2) a concomitant decrease in myocardial oxygen supply (caused by vasoconstriction of the epicardial coronary arteries). beta-adrenergic blocking agents may exacerbate cocaine-induced coronary arterial vasoconstriction, thereby increasing the magnitude of myocardial ischemia. In contrast, nitroglycerin and verapamil reverse cocaine-induced hypertension and coronary arterial vasoconstriction; therefore, they are the agents of choice in treating patients with cocaine-associated chest pain.

Modulation of the effects of norepinephrine uptake inhibitors on the norepinephrine-induced contractile response of the porcine uterine artery during early pregnancy

The effects of norepinephrine (NE) uptake inhibitors on the porcine uterine artery's contractile response to NE and their potential alteration during early pregnancy (Day 13 postcoitus; day of coitus = Day 0) in comparison with the end of the luteal phase (Days 11-14; first day of behavioral estrus = Day 0) was investigated. This pregnancy time point is characterized by a transient increase in resting uterine blood flow dependent on the presence of blastocysts, an increased endometrial vascular permeability, and the beginning of the endometrial attachment of the blastocysts. A cumulative concentration-response curve (CCRC) to NE was produced in isometrically-mounted rings. Cocaine (5 microM) was used to inhibit neuronal NE uptake and hydrocortisone (30 microM) was used to inhibit extraneuronal NE uptake. Either drug alone induced a leftward shift of the CCRC to NE without affecting the maximal response. This shift had the same amplitude at the end of the luteal phase and in early pregnancy. However, the leftward shift induced by cocaine was larger than that induced by hydrocortisone only in early pregnancy, and the leftward shift induced by exposure to both hydrocortisone and cocaine was larger in early pregnancy than at the end of the luteal phase. These results suggest that a significant sensitization of the contractile response of the porcine uterine artery to NE is induced by neuronal and extraneuronal uptake inhibitors and that this effect is altered in early pregnancy, possibly reflecting the existence of a mechanism protecting the uterine artery against excessive sympathetic stimulation.

Effects of cocaine on human and goat isolated cerebral arteries

Cocaine abuse has been increasingly associated with cerebrovascular disease. We have studied the vasoactive properties of cocaine in branches of human middle cerebral artery and in goat middle cerebral artery isolated in an organ bath for isometric tension recording. Cocaine (10(-5) - 3 x 10(-4) M) induced small contractions, while higher concentrations (10(-3) - 3 x 10(-3) M) induced relaxation of human arteries at resting tension. In human arteries precontracted with KCl (50 mM), prostaglandin F- (10(-5) M) or endothelin-1(10(-9) M), cocaine (10(-6) - 3 x 10(-3) M) induced concentration-dependent relaxations which differed in terms of EC50 or maximum effect (Emax). With regard to goat arteries, cocaine (10(-6) - 3 x 10(-3) M) induced almost negligible changes in resting tension, and induced concentration-dependent relaxations of the arterial tone induced with KCl (50 mM). By contrast, goat arteries precontracted with prostaglandin F2 alpha (10(-5) M) or endothelin-1 (10(-9) M) showed biphasic concentration-response curves with concentration-dependent contractions to cocaine (10(-5) - 10(-3) M) and relaxation to the highest concentration (3 x 10(-3) M). Preincubation with cocaine (10(-4) - 10(-3) M) inhibited the contractile responses to CaCl2 (10(-6) - 10(-2) M) in depolarizing, Ca(2+)-free medium, and this inhibition was reversed by preincubation with the Ca2+ entry activator Bay K8644 (10(-10) - 10(-8) M). Therefore, cocaine induces tension changes in cerebral arteries which depend on the species, the arterial tone and the contractile agent inducing it. The relaxant effects could be attributed to the interference of cocaine with the role of Ca2+ in the maintenance of arterial tone, at least in part by blocking Ca2+ entry through membrane channels.

Immediate effects of intravenous cocaine on the thoracic aorta and coronary arteries. A transesophageal echocardiographic study

STUDY OBJECTIVES AND DESIGN: Arterial vasoconstriction is thought to play a role in the etiology of cocaine-induced cardiovascular complications, but little is known about the immediate effects of cocaine on the thoracic aorta and coronary arteries. To examine these effects, we used transesophageal echocardiography to examine the thoracic aorta and coronary arteries before and immediately after intravenous (i.v.) cocaine (1.2 mg/kg) in 15 subjects.

MEASUREMENTS AND RESULTS

Immediately after cocaine infusion, average heart rate, systolic BP, and double product were increased compared with baseline (22%, 15%, 35%, respectively). There was no significant change in the diameters of the ascending aorta (27.5 vs 27.1 mm; p = 0.85), the descending aorta (19.8 vs 20.4 mm; p = 0.62), or the left main coronary artery (4.3 vs 4.7 mm; p = 0.15). However, there was a trend for an increase in coronary blood flow immediately after cocaine (226 vs 309 mL/min; p = 0.10).

CONCLUSIONS

We conclude that in the 15 subjects studied, there was no evidence of thoracic aorta of coronary artery vasoconstriction immediately after i.v. cocaine. Instead, we found that the diameters of the thoracic aorta and the left main coronary artery were unchanged, and that there was a trend for augmentation of coronary artery blood flow.

Cocaine and the porcine coronary microcirculation: effects of chronic cocaine exposure and hypercholesterolemia

OBJECTIVE

To examine the acute effect of cocaine on the coronary microcirculation and whether chronic cocaine administration with or without a concomitant high-cholesterol diet affects beta-adrenoceptor and endothelial functions in the coronary microcirculation.

DESIGN

Prospective experimental study.

SETTING

Laboratory and animal research facility.

PARTICIPANTS

Yorkshire pigs.

INTERVENTIONS

Pigs were fed a high (2%)-cholesterol diet or a regular diet for 3 months. Animals in both groups received cocaine chronically (7 mg/kg/day, IM). Control animals were fed a regular diet.

MEASUREMENTS AND MAIN RESULTS

Responses of the porcine coronary arterioles (90 to 190 microns in diameter) were examined in vitro in a pressurized (40 mmHg) no-flow state using a video-imaging apparatus. Acute application of cocaine caused a significant contraction with a mean maximal diameter decrease of 14% +/- 5%, which was markedly reduced by muscarinic blockade but not significantly affected by alpha 1-adrenergic blockade. Lidocaine or procainamide had no vasoconstrictor effect. Chronic exposure of animals to cocaine diminished contractile responses to cocaine and reduced relaxation responses to the nonselective beta-adrenergic receptor agonist isoproterenol. Phenylephrine caused a minimal (< 4%) contraction of vessels in all groups. Chronic cocaine administration with concomitant high-cholesterol feeding attenuated endothelium-dependent relaxations to serotonin, whereas endothelium-dependent relaxations to bradykinin were unaffected. Endothelium-independent relaxations to sodium nitroprusside were similar in all groups.

CONCLUSIONS

These results suggest that cocaine can exert a direct vasoconstrictor effect on the porcine coronary microcirculation via a muscarinic mechanism. Chronic exposure to cocaine significantly decreases beta-adrenoceptor-mediated relaxation and blunts endothelium-dependent relaxation to a small degree.

Effect of cocaine on the contracture response to 1% halothane in patients undergoing diagnostic muscle biopsy for malignant hyperthermia

Two case reports have cited the recreational use of cocaine as possible trigger of a malignant hyperthermia (MH) crisis. We evaluated whether toxic concentrations of cocaine altered the in vitro muscle response to halothane during contracture tests for MH. Twenty-two patients were studied. Muscle biopsies were obtained and first tested for MH susceptibility with 3% halothane and caffeine contracture testing. Ten patients were diagnosed as MH-susceptible and 12 as MH non-susceptible, in accordance with the North American Malignant Hyperthermia Group protocol. Then, muscle strips were exposed to 1% halothane in the presence and absence of 0.1 mmol.L-1 cocaine. Cocaine alone did not affect baseline muscle tension in either group. With 1% halothane, MH non-susceptible muscle showed no contracture with or without cocaine. In contrast, in the presence of 1% halothane, MH-susceptible muscle showed either no change in contracture (six patients), an increase (two patients), or a decrease (two patients) when exposed to cocaine. However, the overall effect of cocaine on muscle contracture in the presence of 1% halothane was insignificant in both groups. We conclude that cocaine, even at toxic levels, does not have a direct effect on skeletal muscle contractility and thus is safe for MH-susceptible patients.

Cocaine: a review of its toxic actions on cardiac function

It has become increasingly apparent that cocaine abuse can provoke lethal cardiac events, including myocardial infarction and ventricular fibrillation. The mechanisms responsible for these cardiotoxic actions of cocaine largely remain to be determined. Cocaine has two primary pharmacological properties that can adversely affect the heart and vasculature. Cocaine acts both as a local anesthetic (sodium and potassium channel blockade) and as a powerful cardiac stimulant that accentuates the actions of the sympathetic nervous system (inhibition of central and peripheral neuronal catecholamine uptake). The local anesthetic properties could impair impulse conduction, as well as elicit inhomogeneities in repolarization (refractory period), which creates an ideal substrate for reentrant arrhythmias. In addition, high doses of cocaine can depress contractile function due to inhibition of sodium/calcium exchange that results from decreased sodium influx (local anesthetic action). These actions are particularly obvious when sympathomimetic effects of cocaine are blunted. In a similar manner, the cocaine-induced accumulation of catecholamines potentiates the activation of alpha- and beta-adrenergic receptors, which can provoke coronary vasospasm (myocardial ischemia and infarction), increased contractile force (increased metabolic demand), and cardiac arrhythmias. The activation of adrenergic receptors will elicit a cascade of second messengers, ultimately provoking an increase in cytosolic calcium. These elevations in cytosolic calcium can provoke oscillations in membrane potential, triggering sustained action potential generation and extrasystoles. In particular, activation of the alpha IA-adrenergic receptor subtype and corresponding increase in calcium influx via voltage sensitive (L type) channels may play a critical role in the genesis of malignant arrhythmias. Thus, the adrenergic and local anesthetic properties of cocaine could act synergistically to elicit toxic actions on the heart.

Cocaine and benzoylecgonine constrict cerebral arteries by different mechanisms

This study was designed to determine possible mechanisms underlying the vasoconstrictor activity of cocaine and its principal metabolite, benzoylecgonine (BE) in cat isolated cerebral arteries. The arteries constricted significantly in response to single doses of cocaine, BE and norepinephrine (NE; (P < 0.05). After 6-OHDA treatment to remove adrenergic nerve endings, NE-induced constrictions were essentially unchanged from those before treatment. Denervated arteries exposed to cocaine dilated significantly (P < 0.05) but those exposed to BE constricted as much as before denervation. Following exposure to prazosin and yohimbine, arterial constrictions to NE and cocaine were significantly reduced from control (P < 0.05) but the BE-induced constriction was unchanged. Ryanodine eliminated the cocaine-induced contraction (P < 0.05) whereas verapamil eliminated the BE response (P < 0.05). These data suggest that while cocaine's vasoconstrictor action may be significantly mediated through adrenergic transmission, BE may act through a mechanism involving calcium (Ca2+) channels. Cocaine levels peak and decline in the body more rapidly than BE levels which can remain detectable for days. This study suggests there may also be different pharmacological mechanisms as well as temporal differences underlying the vasoreactivity of these two substances. Our findings may have implications for pharmacological management of cocaine-induced toxic vascular events.

The effect of cocaine and desipramine on neuronal uptake of [3H]-noradrenaline and sensitivity to noradrenaline of rat mesenteric resistance arteries

1. The effects of cocaine and desipramine (DMI) on neuronal uptake (uptake1) of [3H]-noradrenaline (NA) and isometric tension development to exogenous NA were assessed in mesenteric resistance arteries of Wistar rats. 2. Both drugs concentration-dependently inhibited [3H]-NA uptake1, DMI being more potent than cocaine. The maximum inhibition produced by each drug was the same as that produced by denervation with 6-hydroxydopamine. In denervated vessels there was no effect of cocaine on [3H]-NA uptake1. 3. Cocaine, in the same concentration range which caused inhibition of uptake1, increased the sensitivity to NA, while DMI, in a concentration range which inhibited uptake1, did not increase the sensitivity to NA and at high concentrations reduced the sensitivity and maximal response to NA. Since DMI affected responses to NA but not responses to vasopressin and potassium its effect is probably related to blockade of alpha 1-adrenoceptors. 4. We conclude that the effect of cocaine on the sensitivity to NA reflects inhibition of uptake1 in rat resistance arteries, while DMI cannot be used to assess the functional effect of uptake1 in this preparation.

Increased prevalence of aortic fatty streaks in cholesterol-fed rabbits administered intravenous cocaine: the role of vascular endothelium

Several recent postmortem studies suggest an increased prevalence of atherosclerosis in young habitual cocaine abusers. However, little is known about the effects of cocaine abuse on the vascular endothelium and its relationship to atherosclerosis. Therefore, the consequence of chronic administration of intravenous cocaine on the induction of aortic sudanophilia was examined. Male New Zealand White rabbits were fed a 0.5% cholesterol diet for 10 wk. During this period, animals were randomized to receive either cocaine-hydrochloride (0.25 mg/kg) intravenously (n = 17) twice daily; or an equivalent volume of 0.9% physiologic saline, control group (n = 16). Mean values for total circulating leukocytes and platelets and total plasma cholesterol and triglycerides were similar in both groups throughout the protocol. At the completion of the study, aortic sudanophilia was measured and expressed as a percentage of regional involvement (R1 = proximal 4 cm, R2 = middle 6 cm, and R3 = distal 10 cm). Statistical significance among groups was achieved in the proximal thoracic aorta (p = 0.057). No significant differences in sudanophilia were noted in the middle and distal segments. When animals were placed in subgroups according to percent total plaque involvement, there was a significant increased distribution of rabbits with a greater extent of sudanophilia in the cocaine-treated group as compared with control (p = 0.01, chi-square analysis). Immunocytochemical studies using the macrophage-specific and muscle actin-specific monoclonal antibodies demonstrated that sudanophilic areas in both groups were predominantly composed of macrophage-derived foam cells. Evaluation of plaque morphology showed an increase in intimal plaque thickness and in the number of macrophages and smooth muscle cells in cocaine-treated animals; however, group differences were not statistically significant. Because no significant differences were found in the cellular composition of atherosclerotic plaques between groups, further studies were performed to assess the effects of cocaine on the permeability function of cultured endothelial cell monolayers as a possible mechanism of increased sudanophilia. Cocaine (100 microM)-treated endothelial cell monolayers demonstrated an increased permeability to horseradish peroxidase during all time intervals studied (0-6 hr). Permeability differences were statistically significant at 30 min and 1 hr (p = 0.003 and 0.02, respectively). Collectively, these observations suggest that administration of cocaine to cholesterol-fed rabbits increases the prevalence of aortic sudanophilia via at least one possible mechanism involving enhanced vascular permeability.

Extracellular Ca(2+)-dependent potentiation by cocaine of serotonin- and norepinephrine-induced contractions in rat vascular smooth muscle

Using front-surface fluorometry, we determined the effects of cocaine on force and cytosolic Ca2+ concentration ([Ca2+]i) in the rat aorta. We also examined the effects of cocaine on 45Ca2+ influx. Cocaine (10(-7) to 10(-4) M) alone did not alter the resting level of [Ca2+]i and force. Cocaine (< 10(-4) M), in a concentration-dependent manner, potentiated the 10(-6) M serotonin (5-HT)-induced or 10(-8) M norepinephrine (NE)-induced sustained increase in [Ca2+]i and force in the presence of extracellular Ca2+, whereas it had no potentiating effects in Ca(2+)-free solution. Similar potentiating effects of cocaine were observed in pharmacologically denervated strips. Cocaine (10(-5) M) produced a leftward shift of concentration-response curves for both 5-HT- and NE-induced increases in [Ca2+]i and force with no effect on the maximal response or the relations between [Ca2+]i and force. Cocaine (10(-5) M also accelerated the 45Ca2+ influx during activation by 10(-6) M 5-HT or by 10(-8) M NE. Cocaine (> 10(-3) M) inhibited 5-HT-, NE-, and high-K+ depolarization-induced contractions accompanied by decreases in [Ca2+]i in normal physiological salt solution and 5-HT- or NE-induced transient increase in [Ca2+]i and force in Ca(2+)-free physiological salt solution. Thus, low concentrations of cocaine potentiate NE- or 5-HT-induced contraction by augmenting the increase in [Ca2+]i. These potentiating effects may derive from either an increase in the affinity of the receptors to agonists or an increase in the Ca2+ influx. On the other hand, high concentrations of cocaine (> 10(-3) M) have a relaxant effect on vascular smooth muscle, as a result of a decrease in [Ca2+]i.

Transient myocardial ischemia in infants prenatally exposed to cocaine

This prospective study examined whether neonates of pregnant women who used cocaine during pregnancy are at a risk for the development of transient myocardial ischemia and altered autonomic function, as in adults. We studied 21 of 35 infants with a history of prenatal exposure to cocaine. The ST segment changes and heart rate variability were evaluated from three-channel Holter monitors within 48 hours of birth. The data were compared with those on 20 control infants with similar birth weight, gestational age, and postnatal age. Six infants (29%) who were exposed to cocaine in utero had transient ST segment elevation, versus only one infant (5%) from the control group (odds ratio = 7.6; 95% confidence interval, 1.14, 50.64). Heart rates, results of total power and low-frequency power spectral analyses for heart rate variability, and arrhythmias were not significantly different in the two groups. However, a lower ratio of low-to high-frequency power reflected increased vagal activity in cocaine-exposed infants. We conclude that cocaine use in pregnant mothers is associated with transient ST segment abnormalities in their infants. These abnormalities are consistent with transient myocardial ischemia.

Transient time course of cocaine-induced cardiac depression versus sustained peripheral vasoconstriction

OBJECTIVES

The goal of this study was to define in vivo the magnitude and temporal course of cocaine-induced cardiac depression separate from peripheral vascular loading changes.

BACKGROUND

Cocaine administration immediately alters arterial pressure, ventricular filling, contractility and heart rate. These combined changes have complicated previous analyses of the cardiac effects of cocaine, because routine measures of function are influenced by all these factors.

METHODS

Pressure-volume loops and relations were measured by conductance catheter technique in 10 intact chest anesthetized dogs before and up to 30 min after administration of cocaine (3 mg/kg intravenously). Heart rate was kept constant by atrial pacing, and data were obtained before and after ganglionic blockade.

RESULTS

Cocaine decreased ejection fraction, cardiac output and maximal rate of rise of left ventricular pressure (dP/dtmax) and increased arterial vascular resistance (all p < 0.05). The maximal change occurred by 2 min and was fully sustained for the next 30 min. In contrast, contractile indexes based on pressure-volume analysis (e.g., end-systolic pressure-volume relation) decreased only briefly at 2 min (by -19%) and returned to control value after 5 to 10 min. Reflex blockade with hexamethonium eliminated cocaine-induced vasoconstriction, but the magnitude and brevity of cardiac depression were unaltered. Ejection fraction, dP/dtmax and cardiac output now also decreased transiently, suggesting that the sustained changes observed before blockade in these variables were load related. Analogous load effects also explained changes in peak filling rate.

CONCLUSIONS

Cocaine induces brief direct cardiac depression that is temporally dissociated from more sustained peripheral vasoconstriction. This dissociation is not measured by traditional left ventricular function analysis because of simultaneous load change. The transience of cardiac depression suggests that it probably does not play a major role in late adverse sequelae of cocaine administration.

The effects of acute and chronic cocaine use on the heart

It is clear that cocaine has cardiotoxic effects. Acute doses of cocaine suppress myocardial contractility, reduce coronary caliber and coronary blood flow, induce electrical abnormalities in the heart, and in conscious preparations increase heart rate and blood pressure. These effects will decrease myocardial oxygen supply and may increase demand (if heart rate and blood pressure rise). Thus, myocardial ischemia and/or infarction may occur, the latter leading to large areas of confluent necrosis. Increased platelet aggregability may contribute to ischemia and/or infarction. Young patients who present with acute myocardial infarction, especially without other risk factors, should be questioned regarding use of cocaine. As recently pointed out by Cregler, cocaine is a new and sometimes unrecognized risk factor for heart disease. Acute depression of LV function by cocaine may lead to the presence of a transient cardiomyopathic presentation. Chronic cocaine use can lead to the above problems as well as to acceleration of atherosclerosis. Direct toxic effects on the myocardium have been suggested, including scattered foci of myocyte necrosis (and in some but not all studies, contraction band necrosis), myocarditis, and foci of myocyte fibrosis. These abnormalities may lead to cases of cardiomyopathy. Left ventricular hypertrophy associated with chronic cocaine recently has been described. Arrhythmias and sudden death may be observed in acute or chronic use of cocaine. Miscellaneous cardiovascular abnormalities include ruptured aorta and endocarditis. Most of the cardiac toxicity with cocaine can be traced to two basic mechanisms: one is its ability to block sodium channels, leading to a local anesthetic or membrane-stabilizing effect; the second is its ability to block reuptake of catecholamines in the presynaptic neurons in the central and peripheral nervous system, resulting in increased sympathetic output and increased catecholamines. Other potential mechanisms of cocaine cardiotoxicity include a possible direct calcium effect leading to contraction of vessels and contraction bands in myocytes, hypersensitivity, and increased platelet aggregation (which may be related to increased catecholamine). The correct therapy for cocaine cardiotoxicity is not known. Calcium blockers, alpha-blockers, nitrates, and thrombolytic therapy show some promise for acute toxicity. Beta-Blockade is controversial and may worsen coronary blood flow. In patients who develop cardiomyopathy, the usual therapy for this entity is appropriate.

Chronic cocaine administration decreases norepinephrine-induced phosphoinositide hydrolysis in rat aorta

The effect of chronic cocaine administration on norepinephrine stimulated hydrolysis of inositol 1,4,5-trisphosphate from the membrane phosphatidylinositol phosphate pool in isolated rat aorta was investigated. Rats received saline (controls), or 10 or 20 mg/kg cocaine once a day for 15 days. This treatment resulted in a dose-dependent reduction in norepinephrine (0.36 microM) stimulated phosphoinositide hydrolysis. The effect of acute cocaine was determined by adding 30 microM cocaine to the in vitro incubation solution. When aortas were exposed to cocaine and norepinephrine simultaneously, in vitro, inositol phosphate formation doubled. By itself, cocaine did not affect phosphoinositide hydrolysis. Contraction of aortic helical strips by norepinephrine decreased in tissues from rats chronically treated with 20 mg/kg cocaine. In vitro cocaine shifted the norepinephrine concentration/response curve to the left and increased the maximum response. Neither acute nor chronic cocaine treatment affected prazosin's apparent dissociation constant, suggesting that cocaine did not affect receptor affinity. These data suggest that chronic, but not acute cocaine administration may interfere with pharmacomechanical coupling in rat aorta.