Cerebrovascular and cerebral metabolic effects of flurazepam and a benzodiazepine antagonist, 3-hydroxymethyl-beta-carboline

Respiratory mu-opioid and benzodiazepine interactions in the unrestrained rat

Interactions of mu-opioid receptors with the benzodiazepine system were studied by examining the modulatory effects of flumazenil (a benzodiazepine antagonist) and alprazolam (a benzodiazepine agonist) on the respiratory effects of the opioid peptide dermorphin. Dermorphin, 1-30 nmol administered i.c.v., to conscious, unrestrained rats decreased ventilation rate (VR) and minute volume (MV) dose-dependently. The ventilatory depression was antagonized by naloxone and by the benzodiazepine antagonist flumazenil. The benzodiazepine alprazolam potentiated the respiratory inhibition of a small (1 nmol) dose of dermorphin but antagonized that of a higher dose (3 nmol). The results suggest that the benzodiazepine/GABA receptor complex modulates respiratory depression induced by central mu-receptor stimulation in the rat.

Cerebral blood flow during ACTH therapy: especially diurnal changes within the first week of therapy

Changes in cerebral blood flow (CBF) were evaluated in children with epilepsy treated with adrenocorticotrophic hormone (ACTH) by the Doppler ultrasound method. The average maximal blood velocity (A/L) and maximal end-diastolic blood velocity (d) of the internal carotid artery, as indices of CBF, significantly decreased during ACTH therapy. These values had already decreased at 30 minutes after the first injection of ACTH and were hardly restored 24 hours later just before the next injection. Such changes repeatedly occurred for the first four days of therapy so that the reductions in the A/L and d values proceeded in a stepwise manner. These values became minimum at around one week after initiation of the therapy and then gradually increased, returning to the original levels by the 8th week of therapy. Investigation of the changes in cerebral metabolism seemed to be the next step for elucidation of the mechanism underlying the CBF reduction during ACTH therapy.

The interaction between benzodiazepine antagonists and barbiturate-induced cerebrovascular and cerebral metabolic depression

It has been reported that pentobarbital facilities binding to benzodiazepine receptors binding at anesthetic concentrations and that this action may play a role in the anesthetic potency of this barbiturate. The interaction between pentobarbital and benzodiazepine receptors was tested with Ro 15-1788 which is reported to be a pure benzodiazepine antagonist and 3-hydroxymethyl-beta-carboline (3-HMC), an antagonist which has inverse activity alone. Cerebral blood flow (CBF) and cerebral oxygen consumption (CMRO2) were measured in rats after injections of pentobarbital with and without the antagonists. Pentobarbital produced dose-dependent decreases in cerebral blood flow and cerebral oxygen consumption at 15 and 30 mg/kg. The antagonist Ro 15-1788 (10 mg/kg) stimulated cerebral blood flow and cerebral oxygen consumption alone but did not alter the cerebral depression produced by pentobarbital. The cerebral metabolic stimulation produced by Ro 15-1788 was unexpected since the drug is reported to be a pure antagonist without agonistic activity, but the lack of effect on pentobarbital-induced cerebral depression is consistent with other reports. 3-Hydroxymethyl-beta-carboline at 10 mg/kg did not stimulate cerebral blood flow and cerebral oxygen consumption but significantly antagonized the decrease in cerebral oxygen consumption produced by 15 mg/kg pentobarbital. 3-Hydroxymethyl-beta-carboline had no significant effect on decreases in cerebral blood flow and cerebral oxygen consumption produced by phenobarbital, a barbiturate which is reported not to alter binding to benzodiazepine receptors. The ability of 3-HMC to antagonize the effects of pentobarbital would be consistent with an action of both drugs at the benzodiazepine receptor but not by altering binding to an endogenous receptor.

A benzodiazepine antagonist inhibits the cerebral metabolic and respiratory depressant effects of fentanyl

It is reported that benzodiazepines such as diazepam will stimulate the opiate receptor system and that B-carboline drugs, which are benzodiazepine antagonists, may interact with opiate receptors directly. The ability of 3-hydroxymethyl-B-carboline (3-HMC) to antagonize several parameters of fentanyl anesthesia was tested here in rats. Fentanyl (25 and 100 micrograms/kg iv) produced dose dependent depression of cerebral blood flow (CBF), measured by radioactive microspheres, and cerebral oxygen consumption (CMRO2). These effects were significantly inhibited by 10 mg/kg 3-HMC iv. To test for the specificity of this effect, 3-HMC was also given to rats ventilated with inspire concentrations of 2% halothane. Halothane depressed CMRO2 equally in 3-HMC and vehicle treated rats, indicating no significant effect of the benzodiazepine antagonist. Blood pressure was increased in 3-HMC compared to vehicle treated animals during both fentanyl and halothane anesthesia. CBF was increased in 3-HMC vs vehicle treated rats during halothane anesthesia but this could be accounted for by the elevated blood pressure and lack of cerebral autoregulation rather than a direct cerebrovascular effect. 3-HMC decreased the sleep time and respiratory depressant effects of fentanyl but enhanced the analgesic effects of the opiate, as measured by time to respond to a hot plate stimulus. These results indicate that 3-HMC has the ability to specifically antagonize fentanyl anesthesia. These effects may be produced by an action of 3-HMC at the benzodiazepine receptor and/or by an action of the B-carboline at opioid receptors.