Comparison of cerebrovascular effects of intravenous cocaine injection in fetal, newborn, and adult sheep

Death temporally related to the use of a Beta adrenergic receptor antagonist in cocaine associated myocardial infarction

INTRODUCTION

Although it is commonly stated that the use of beta adrenergic receptor antagonists is contraindicated in patients with cocaine toxicity, actual clinical evidence of harm is lacking. This case helps to highlight the risks of beta adrenergic receptor antagonists in patients with chest pain associated with cocaine use.

CASE REPORT

A 54-year-old man was brought to the emergency department (ED) complaining of chest pain after using approximately 1 gram of intranasal cocaine. Aspirin and nitroglycerin spray relieved his pain. Although he remained pain free, tachycardia persisted despite 15 mg of diazepam intravenously. Nearly two hours after presentation, a total of 5 mg of metoprolol was given for persistent tachycardia (115/minute) and an elevated troponin. Shortly thereafter, the patient complained of crushing substernal chest pain, developed pulseless electrical activity, and could not be resuscitated.

DISCUSSION

The administration of beta adrenergic receptor antagonists exacerbates cocaine-induced lethality in animals. In humans given smaller doses of cocaine, beta adrenergic receptor antagonists exacerbate coronary vasoconstriction. Both effects are presumed to occur through unopposed alpha adrenergic receptor agonism. Despite these data, actual cases describing adverse effects in cocaine users given beta adrenergic receptor antagonists are uncommon. This case supports the potential lethality of a cocaine-beta adrenergic receptor antagonist interaction.

The role of peripheral Na(+) channels in triggering the central excitatory effects of intravenous cocaine

While alterations in dopamine (DA) uptake appear to be a critical mechanism underlying locomotor and reinforcing effects of cocaine (COC), many centrally mediated physiological and affective effects of this drug are resistant to DA receptor blockade and are expressed more quickly following an intravenous (i.v.) injection than expected based on the dynamics of drug concentration in the brain. Because COC is also a potent local anesthetic, its rapid action on Na+ channels may be responsible for triggering these effects. We monitored temperatures in the nucleus accumbens, temporal muscle and skin together with conventional locomotion during a single i.v. injection of COC (1 mg/kg), procaine (PRO, 5 mg/kg; equipotential anesthetic dose), a short-acting local anesthetic drug that, like COC, interacts with Na+ channels, and cocaine methiodide (COC-MET, 1.31 mg/kg, equimolar dose), a quaternary COC derivative that is unable to cross the blood-brain barrier. In this way, we explored not only the importance of Na+ channels in general, but also the importance of central vs. peripheral Na+ channels specifically. COC induced locomotor activation, temperature increase in the brain and muscle, and a biphasic temperature fluctuation in skin. Though PRO did not induce locomotor activation, it mimicked, to a greater degree, the temperature effects of COC. Therefore, Na+ channels appear to be a key substrate for COC-induced temperature fluctuations in the brain and periphery. Similar to PRO, COC-MET had minimal effects on locomotion, but mimicked COC in its ability to increase brain and muscle temperature, and induce transient skin hypothermia. It appears therefore that COC's interaction with peripherally located Na+ channels triggers its central excitatory effects manifested by brain temperature increase, thereby playing a major role in drug sensing and possibly contributing to COC reinforcement.

The role of peripheral and central sodium channels in mediating brain temperature fluctuations induced by intravenous cocaine

While cocaine's interaction with the dopamine (DA) transporter and subsequent increase in DA transmission are usually considered key factors responsible for its locomotor stimulatory and reinforcing properties, many centrally mediated physiological and psychoemotional effects of cocaine are resistant to DA receptor blockade, suggesting the importance of other non-DA mechanisms. To explore the role of cocaine's interaction with Na+ channels, rats were used to compare locomotor stimulatory and temperature (NAcc, temporal muscle and skin) effects of repeated iv injections of cocaine (1 mg/kg) with those induced by procaine (PRO 5 mg/kg), a short-acting local anesthetic with negligible effect on the DA transporter, and cocaine methiodide (COC-MET 1.31 mg/kg), a quaternary cocaine derivative that is unable to cross the blood-brain barrier. While PRO, unlike cocaine, did not induce locomotor activation, it mimicked cocaine in its ability to increase brain temperature following the initial injection and to induce biphasic, down-up fluctuations following repeated injections. This similarity suggests that both these effects of cocaine may be driven by its action on Na+ channels, a common action of both drugs. While COC-MET also did not affect locomotor activity, it shared with cocaine and PRO their ability to increase brain temperature but failed to induce temperature decreases after repeated injections. These findings point toward activation of peripheral Na+ channels as the primary mechanism of rapid excitatory effects of cocaine and inhibition of centrally located Na+ channels as the primary mechanism for transient inhibitory effects of cocaine. DA receptor blockade (SCH23390+eticlopride) fully eliminated locomotor stimulatory and temperature-increasing effects of cocaine, but its temperature-decreasing effects remained intact. Surprisingly, DA receptor blockade also altered the temperature fluctuations caused by PRO and COC-MET, suggesting that some of the central effects triggered via Na+ channels are in fact DA-dependent. Finally, repeated administration of PRO to animals that had previous cocaine experience led to conditioned locomotion and potentiated temperature-increasing effects of this drug. It appears, therefore, that, in addition to the central effects of cocaine mediated via interaction with the DA transporter and potentiation of DA uptake, interaction with peripheral and central Na+ channels is important for the initial physiological and, perhaps, affective effects of cocaine, likely contributing to the unique abuse potential of this drug.