Potentiation of morphine analgesia by caffeine.

Significant potentiation of morphine (5 mg kg-1 s.c. or 1 mg kg-1 i.v.) analgesia (tail-withdrawal reflex at 55 degrees C) was observed in caffeine-treated (100 mg kg-1 i.p.) rats as compared to the control group and lower doses of caffeine (2mg kg-1 i.p.) did not show this effect. Potentiated analgesia was reversed by naloxone. Pharmacokinetic or dispositional factors appear to be involved in part in this potentiation.

Comparative effects of cocaine and pseudococaine on EEG activities, cardiorespiratory functions, and self-administration behavior in the rhesus monkey.

The effects of cocaine and pseudococaine on the EEGs, heart and respiratory rates, and self-administration behavior were studied in rhesus monkeys. An intravenous injection of cocaine (2.5 and 4.0 mg/kg) in the monkey produced low-voltage fast waves (LVFWs) in the EEGs and behavioral hyperexcitation accompanied by marked increases in the heart and respiratory rates with mydriasis and excessive salivation. In contrast, pseudococaine produced high-voltage slow waves (HVSWs) in the EEGs and behavioral depression accompanied by the same symptoms of the autonomic functions as those produced by cocaine. Both isomers were self-administered by the monkeys. During cocaine self-administration sessions, the animals showed hyperexcitation in their overall behavior, while with pseudococaine they showed almost normal behavioral responses. These results suggest that cocaine produced excitatory effects and pseudococaine inhibitory effects on the EEGs and behavior. Both isomers stimulate the heart and respiratory rates, and were self-administered by the monkeys.

Comparison of the convulsant effects of cocaine and pseudococaine in the rhesus monkey.

The convulsant effects of cocaine and its C2-epimer, pseudococaine on EEG, respiration, heart rate and behavior were studied in the rhesus monkeys with electrodes implanted in the brain. Intravenous injections of cocaine (3.0 to 8.0 mg/kg) and pseudococaine (3.0 to 7.0 mg/kg) in the animals produced a similar pattern of clonic convulsions accompanied by marked increases in the heart and respiratory rates with mydriasis and excessive salivation. However, both isomers showed different effects on the EEG and animal's behavior following convulsions; e.g., the cocaine-induced convulsions were followed by low-voltage fast waves in the EEGs associated with behavioral hyperexcitation, while pseudococaine-induced convulsions were followed by high-voltage slow waves associated with behavioral depression and drowsiness with intermittent sleep. Pseudococaine was more potent than cocaine in producing convulsions in the same monkeys. The durations of convulsions produced by these drugs were dose-dependent.

Cocaine and pseudococaine: comparative effects on electrical after-discharge in the limbic system of cats.

The effects of cocaine and its dextroisomer pseudococaine on electrical after-discharge (AD) evoked by electrical stimulation of the hippocampus or amygdala were studied in cats with electrodes implanted in the brain. Intravenous injection of cocaine (2.0 to 4.0 mg/kg doses) produced a suppressive effect on the AD while producing low-voltage fast waves (LVFWs) in the electrical activities of the brain (EEG) associated with behavioral excitation. In contrast, pseudococaine at the same dose as cocaine failed to show a significant suppressive effect on the AD except at high doses (5.0 mg/kg). Pseudococaine produced high-voltage slow waves (HVSWs) in the EEG associated with behavioral depression. A linear dose-response relationship was observed for the suppressive effect of cocaine on the AD. The results suggested that the limbic system may be involved as a primary site of action of cocaine in the central nervous system (CNS).

A long-acting buprenorphine delivery system.

A subcutaneously implantable buprenorphine delivery system utilizing cholesterol-glyceryltristearate matrix for prolonged release of drug is described. Implantable cylindrical pellets of buprenorphine (cholesterol 36 mg, glyceryltristearate 4 mg, buprenorphine hydrochloride 10 mg), diameter 3 mm, length 6 mm blocked the antinociceptive action (hot plate, 55 degrees C) of 10 mg kg-1 SC challenge dose of morphine in rats for 12 weeks or more (longer periods not evaluated). The cumulative percent release of buprenorphine from the test devices 2, 4, 6, 10 and 12 weeks after implantation was 27.4, 35.9, 37.6, 39.9 and 43.1, respectively. The release of buprenorphine from 10 mg pellets approximated first-order kinetics with half-lives of 0.85 and 50.24 weeks, for alpha and beta phases, respectively. The test devices possess the desirable characteristics of simplicity, biocompatibility, nontoxicity, ease of sterilization with ethylene oxide, small size for ease of insertion and removal, minimal encapsulation by surrounding tissue and an extended period of drug release unaffected by body metabolism. No side effects were seen in implanted rats which fed well and gained weight during entire treatment. Neither deterioration of implant nor any gross anatomic changes at implant site were apparent 12 weeks after pellet implantation.

Potentiation of morphine analgesia by subanesthetic doses of pentobarbital.

Pentobarbital pretreatment reportedly either inhibits, enhances or has no effect on morphine analgesia. The effect of subanesthetic doses of sodium pentobarbital (8-12 mg kg-1, SC) delivered via a delivery system on analgesia of morphine (5 mg kg-1, SC or 1 mg kg-1, IV) acutely administered 45 min after the sodium pentobarbital pellet implantation was assessed using the warm water (55 degrees C)-induced tail-withdrawal reflex in male Wistar rats. Significant potentiation of morphine analgesia was observed in sodium pentobarbital as compared to the placebo-pelleted animals. Pharmacokinetic or dispositional factors were not involved in this potentiation, which was possibly due to the activation of the descending inhibitory control pathways of nociceptive spinal tail-withdrawal reflex by a combined interaction of two drugs at spinal and supraspinal sites of action, that mediate opiate antinociception.

Effect of caffeine on cocaine locomotor stimulant activity in rats.

The effect of caffeine on the locomotor stimulant activity induced by intravenous cocaine in rats was investigated. Low doses of caffeine (20 mg/kg IP) potentiated the locomotor activity induced by 1, 2.5 mg/kg intravenous doses of cocaine and higher doses of caffeine (50, 100 mg/kg IP) had no significant effect. The locomotor stimulant effect of 20 mg/kg IP dose of caffeine per se in vehicle was significantly higher and that with 100 mg/kg dose significantly lower than that of the vehicle control. Thus caffeine produced dose-dependent effects on cocaine-induced locomotor stimulant activity, with low dose potentiating and higher doses having no significant effect on such activity. Pharmacokinetic or dispositional factors did not appear to play a role in potentiation of cocaine locomotor stimulant activity by caffeine.

Effect of acute and chronic ethanol pre-treatment on the disposition of phencyclidine (PCP) in the rat.

Disposition of [H] Phencyclidine in brain, plasma and adipose tissue of rats acutely and chronically-treated with ethanol was studied using a method possessing high sensitivity and specificity for PCP. In rats acutely-treated with ethanol (5 g/kg PO dose) and PCP (10 mg/kg IP dose), dispositional factors did not play a role in the intensifies pharmacological and behavioral effects of PCP. However in rats chronically-treated with 2.5 g/kg PO dose of ethanol twice a day for 19 days, the disposition of PCP (5 mg/kg IP dose) was significantly altered and the values of PCP in brain, plasma and adipose tissue were significantly higher than those in the control group. Although inhibition of PCP metabolism and a comparatively slower rate of its elimination appear to account for the potentiation of drug effects in animals chronically-treated with ethanol, interaction of drugs at the level of the central nervous system cannot be ruled out.

Intravenous kinetics and metabolism of [15,16-3H]naltrexonium methiodide in the rat.

After a 4 mg kg-1 bolus intravenous dose of [15,16-3H]naltrexonium methiodide to the rat, brain to plasma concentration ratios of the compound were 0.031 to 0.228 between 0.25 to 6 h after injection and the t 1/2 beta in plasma and brain were 2.92 and 7.61 h, respectively. Ethyl acetate-extracted radioactivity due to metabolites in plasma decayed with t 1/2 beta 1.83 h and the ratios of plasma concentration of metabolites to quaternary compound between 0.25 and 6 h were 0.014-0.026. Only unconjugated 7,8-dihydro-14-hydroxynormorphine, naltrexone and traces of 7,8-dihydro-14-hydroxynormorphinone were the metabolites in plasma. Naltrexone (but not normetabolites) was present only in traces in brain up to 0.5 h after injection and not at later times.

Increased brain uptake of morphine in the presence of the antihistamine tripelennamine.

Disposition of [6 3H (N)]morphine in plasma, brain and liver of rats was studied 15 min after intravenous injection of either a 2 mg kg-1 dose of morphine or a combination of the same dose of morphine with a 6 mg kg-1 dose of tripelennamine. The concentrations of morphine in brain and the brain to plasma morphine ratios in animals receiving the combination of drugs concurrently were significantly higher than those in the control morphine group. No significant differences were seen in the morphine or morphine metabolite concentrations in plasma and liver or liver to plasma morphine concentration ratios in the 2 groups. Data suggest that pharmacokinetic factors play a role in the potentiation of opiate effects by antihistamine on concurrent i.v. administration of the two drugs.

Effect of diamorphine, delta 9-tetrahydrocannabinol and ethanol on intravenous cocaine disposition.

The disposition of cocaine (1 mg kg-1) was altered by diamorphine (0.1 mg kg-1) and that of morphine (1 mg kg-1) was altered after their concurrent administration as a bolus i.v. injection to rats by cocaine, without any changes in the metabolism of the drugs. delta 9-Tetrahydrocannabinol (10 mg kg-1 i.p.) did not affect the cocaine disposition. Chronic ethanol treatment (2.5 g kg-1 orally twice daily for 16 days) produced a significantly higher brain-to-plasma cocaine concentration ratio than did saline as control, without any changes in cocaine metabolism.