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Controlled delivery of drugs has been achieved successfully by use of asymmetric membranes. In our study, we have evaluated the influence of various preparation parameters such as concentration of the polymer, concentration of the pore former and temperature of the precipitation bath on the permeability and the release characteristics of propranolol. Propranolol tablets were prepared by direct compression and were coated with varying concentrations of cellulose acetate and glycerin. The coat was precipitated in water, maintained at various temperatures, followed by air drying of the coat. Scanning Electron Microscopy (SEM) was used to characterize the asymmetric structure of the membrane. The influence of various preparation parameters on the release of propranolol from asymmetric coated tablets was evaluated. SEM confirmed the asymmetric nature of the membrane. A zero order release of propranolol was obtained from the coated tablets of propranolol. Various preparation parameters studied significantly affected (p<0.05) the release of propranolol hydrochloride from the asymmetric membrane coated tablets and the release was independent of the pH and the rate of agitation of the dissolution medium (p>0.05). Asymmetric membranes can be successfully utilized in the controlled delivery of highly water soluble drugs like propranolol and by modifying preparation parameters like polymer concentration, pore former concentration and temperature of the precipitation bath, desired release rates can be obtained.

A simple, rapid, and stability indicating reversed-phase high-performance liquid chromatography (HPLC) method of analysis for budesonide, a novel glucocorticoid prescribed for inflammatory bowel disease, was successfully developed. Budesonide is an epimeric mixture and both the epimers have similar anti-inflammatory activity. All the analytical methods reported in the literature are long and are based on separation of the epimers, thus our objective was to obtain a single sharp peak of the drug and to separate the drug peak from all the other degradation products. The method, was used to quantify budesonide in the developed formulation, employed a Kromasil C8, (150 mm x 4.6 mm) column with an isocratic mobile phase of acetonitrile-phosphate buffer (pH 3.2-0.025 M) (55:45 v/v), at a flow rate of 1.1 mL/min. Budesonide was detected by an ultraviolet detector at 244 nm. The method was validated for linearity, precision, repeatability, sensitivity, and selectivity. Selectivity was validated by subjecting stock solution of budesonide to acidic, basic, oxidative, and thermal degradation. The retention time of budesonide was about 4 min with symmetrical peaks. The method was linear over a concentration range 1-50 microg/mL (R2=0.9995). The limit of detection of budesonide was 0.1 microg/mL and the limit of quantitation was 0.25 microg/mL. The peaks of the degradation products did not interfere with the peak of budesonide. The developed method was used to quantify budesonide in budesonide-loaded micro-particles. Excipients present in the micro-particles did not interfere with the analysis and the recovery of budesonide from micro-particles was quantitative.

A simple, rapid and stability-indicating reverse-phase high-performance liquid chromatography (HPLC) method was developed for the assay of halofantrine (HF) base, 1,3-dichloro-alpha-[2-(dibutylamino)ethyl]-6-(trifluoromethyl)-9-phenanthrenemethanol. The HPLC method was validated for precision, accuracy, selectivity and linearity and range. It was used to assay for HF base in solid dispersions. Excellent linearity was observed between HF base concentration and the peak area (R(2)=0.9998). The limit of detection was 1 ng (with a signal-to-noise ratio of 2:1), and the limit of quantitation was 10 ng (with a signal-to-noise ratio of 10:1). The method proved to be selective. Selectivity was validated by subjecting a stock solution of HF to acidic, basic, oxidative and thermal degradations. The peaks of the degradation products did not interfere with the peak of HF. Excipients present in the solid dispersions did not interfere with the analysis.

The effects of chronic administration of cocaine and its subsequent withdrawal on the binding of [3H]MK-801, an antagonist of the N-methyl-D-aspartate (NMDA) receptor, to brain regions and spinal cord of the mouse was determined. Chronic administration of cocaine (10 mg/kg, SC) twice a day for 7 days sensitized male Swiss-Weber mice to its locomotor activity, as evidenced by a greater locomotor activity in comparison with vehicle-injected controls. In nonwithdrawing mice, the binding of [3H]MK-801 was increased in the cerebellum and spinal cord but was decreased in the cortex and hypothalamus. On the other hand, during withdrawal from cocaine, a significant decrease in the binding of [3H]MK-801 was observed only in the cortex, but the changes in the cerebellum, spinal cord and hypothalamus were normalized. It is concluded that, in the mouse, sensitization to the locomotor activating action of cocaine is associated with differential changes in the NMDA receptors of the central nervous system.

1. Chronic administration of L-arginine (200 mg/kg, i.p) twice a day for 4 days decreased the antinociceptive response to subcutaneously, but not to intracerebroventricularly, administered morphine in male Swiss-Webster mice, as measured by the tail-flick test. 2. The decreased antinociceptive response to morphine was reversed by concurrent administration of NG-nitro-L-arginine (L-NNA) (5 mg/kg, IP), an inhibitor of nitric oxide synthase. 3. The concentrations of morphine in mice treated chronically with L-arginine and then given morphine (10 mg/kg, SC) were determined in the peripheral tissues. L-Arginine treatment significantly increased the concentration of morphine in spleen and lungs, did not modify it in liver, kidneys and urine. L-NNA by itself had no effect on the distribution of morphine in peripheral tissues but reversed the changes induced by chronic treatment with L-arginine. 4. Acute administration of L-arginine (200 mg/kg, IP) did not modify either the morphine antinociception or the morphine distribution in peripheral tissues. 5. Previous studies from this laboratory indicated that chronic treatment with L-arginine decreases the concentration of morphine in several brain regions and spinal cord of mice. 6. The facts that chronic treatment with L-arginine does not alter antinociception induced by ICV administered morphine and it increases the concentration of morphine in peripheral tissues while decreasing it in brain regions after peripheral administration of morphine suggest that the decreased antinociception induced by subcutaneously administered morphine may be related to its decreased entry into the brain.

Male Swiss-Webster mice were injected intracerebroventricularly (i.c.v.) with [D-Pen2,D-Pen5]enkephalin (20 microg/mouse) twice a day for 2 days. This procedure resulted in down-regulation of binding sites for [3H][D-Pen2,D-Pen5]enkephalin as evidenced by a 52% decrease in the Bmax value. Twice daily injections of (+)-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]-cyclohepten-5,10-imine (MK-801) (0.1 mg/kg, i.p.) or [(-)3-SR,4a-RS,8a-SR-6-(phosphonomethyl)-1,2,3,4,4a,5,6,7,8,8a-decahy droisoquinoline-3-carboxylic acid] (LY 235959) (2 mg/kg, i.p.), the noncompetitive and competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor, respectively, for 2 days did not alter the Bmax or Kd value of [3H][D-Pen2,D-Pen5]enkephalin binding to the mouse brain. Concurrent treatment of MK-801, but not of LY 235959 with [D-Pen2,D-Pen5]enkephalin, reversed the decreases in Bmax value of [3H][D-Pen2,D-Pen5]enkephalin. Twice daily injections of [D-Ala2,Glu4] deltorphin II (20 microg/mouse) for 2 days caused an increase in the Kd value, but not the Bmax value of [3H][D-Pen2,D-Pen5]enkephalin to bind to brain membranes. Concurrent treatment of [D-Ala2,Glu4]deltorphin II with LY 235959 reversed the increase in Kd value of [3H][D-Pen2,D-Pen5]enkephalin binding induced by multiple injections of [D-Ala2,Glu4]deltorphin II, but MK-801 had no effect. The results suggest that multiple injections of delta1- and delta2-opioid receptor agonists down-regulate delta1-opioid receptors of the brain by modifying Bmax and Kd values of [3H][D-Pen2,D-Pen5]enkephalin binding, respectively. MK-801 and LY 235959 reverse delta1- and delta2-opioid receptor agonists-induced down-regulation of brain delta1-opioid receptor, respectively, apparently by different mechanisms. It is concluded that short term treatment of mice with delta1-opioid receptor agonist down-regulates brain delta1-opioid receptors by decreasing Bmax of the ligand which is partially reversed by concurrent treatment with MK-801 but not by LY 235959. On the other hand, short term treatment of mice with delta2-opioid receptor agonist down-regulates brain delta1-opioid receptors by increasing Kd of the ligand which is partially reversed by concurrent treatment with LY 235959 but not by MK-801.

1. The time course of the effects of multiple injections of U-50,488H, a kappa-opioid receptor agonist, and its subsequent termination on its analgesic action and nitric oxide synthase (NOS) activity was determined in the brain regions and spinal cord of the mouse. 2. Male Swiss-Webster mice were rendered tolerant to U-50,488H by twice-daily injections of the drug (25 mg/kg, IP) for 4 days. Vehicle-injected mice served as controls. 3. In tolerant mice, NOS activity was unchanged in brain regions and the spinal cord after treatment with U-50,488H. During abstinence from U-50,488H, NOS activity was found to be increased in the cortex and remainder of the brain, but no change was noted in the cerebellum, midbrain and spinal cord. 4. These studies demonstrate that withdrawal from the short-term treatment with U-50,488H in mice causes induction of NOS in certain brain regions. However, long-term treatment and withdrawal from U-50,488H are not associated with changes in the central NOS activity and indicate a possible adaptation in the NOS activity.

1. The time course of the effect of chronic administration of morphine on the activity of nitric oxide synthase (NOS) in the brain regions and spinal cord of the mouse was determined. The effect of naltrexone by itself on the NOS activity and that induced by morphine also were determined. 2. Male Swiss Webster mice were implanted subcutaneously with a pellet containing 25 mg of morphine free base for 4 days. Placebo pellet implanted mice served as controls. 3. Twenty-four hours after treatment with morphine, NOS activity decreased in the cerebellum, midbrain, cortex and remainder of the brain as well as in the spinal cord. Forty-eight and 72 hr after the treatment with morphine, NOS activity increased in the cerebellum and cortex, but no change was observed in the other brain regions and spinal cord. Twenty-four hours after morphine pellet removal (withdrawal), NOS activity in all brain regions and the spinal cord has returned to normal. 4. Implantation of a pellet containing 10 mg of naltrexone did not alter NOS activity in any brain region or spinal cord for 24, 48 and 72 hr or 24 hr after removal of the pellet. 5. Implantation of a naltrexone pellet in conjunction with a morphine pellet blocked the changes in NOS activity in the brain region and spinal cord induced by morphine. 6. It is concluded that the initial decrease in NOS activity by morphine may be related to enhanced motor activity, whereas the increase in NOS activity in certain brain regions may be associated with tolerance-physical dependence development. Additionally, the changes in central NOS activity by morphine appear to be mediated by opioid receptors because they were blocked by concurrent treatment with naltrexone.

1. The effects of LY 235959, a competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor, on the analgesic and hypothermic actions of morphine, were determined in nontolerant and morphine-tolerant mice. 2. LY 235959 enhanced the analgesic and hypothermic action of morphine in nontolerant mice. 3. LY 235959 also enhanced the analgesic and hypothermic actions of morphine in morphine-tolerant mice. LY 235959, injected before saline injection, had no effect on the antinociception or the body temperature. 4. It is concluded that competitive antagonism of the NMDA receptor enhances the pharmacologic actions of morphine both in morphine-naive and morphine-tolerant mice and that these actions differ from the noncompetitive antagonism of the NMDA receptors.

The effects of chronic administration of 7-benzylidene-7-dehydronaltrexone, a delta 1-opioid receptor antagonist and naltriben, a delta 2-opioid receptor antagonist, on the antinociceptive responses to [D-Pen2, D-Pen5] enkephalin and [D-Ala2, Glu4]deltorphin II, delta 1- and delta 2-opioid receptor agonists, respectively, were determined in the mouse. Female B6C3F1 mice were given 7-benzylidene-7-dehydronaltrexone (3 mg/kg/day), naltriben (1 mg/kg/day) or the vehicle by subcutaneously implanted Alzet osmotic minipumps for 7 days. Both [D-Pen2, D-Pen5]enkephalin and [D-Ala2, Glu4]deltorphin II administered intracerebroventricularly (i.c.v.) produced antinociceptive as measured by the tail-flick test with ED50 values of 6.76 and 6.68 micrograms/mouse, respectively. Chronic administration of 7-benzylidene-7-dehydronaltrexone lowered the ED50 of [D-Pen2, D-Pen5]enkephalin but not of [D-Ala2, Glu4]deltorphin II. Chronic administration of naltriben lowered the ED50 of [D-Ala2, Glu4]deltorphin II but had no effect on the ED50 of [D-Pen2, D-Pen5]enkephalin. The binding of [3H][D-Pen2, D-Pen5]enkephalin to whole brain membranes of chronic 7-benzylidene-7-dehydronaltrexone-treated mice did not differ from chronic vehicle-treated mice. On the other hand, chronic administration of naltriben resulted in slight but reproducible elevation in the Bmax value of [3H][D-Pen2, D-Pen5]enkephalin to bind to whole brain membranes in comparison to vehicle-injected controls. The results suggest that chronic treatment with delta 1- and delta 2-opioid receptor antagonist cause behavioral supersensitivity to their agonists, respectively, and provides further evidence for the existence of delta-opioid receptor subtypes.

1. The effects of morphine tolerance and abstinence on the binding of [3H]MK-801, a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) receptors were determined in brain regions and spinal cord of the mouse. 2. Male Swiss-Webster mice were rendered tolerant to and physically dependent on morphine by subcutaneous implantation of a pellet containing 75 mg of morphine base for 3 days. Placebo pellet-implanted mice served as controls. In tolerant (nonabstinent) mice, the pellets were left intact at the time of sacrificing whereas, in the abstinent mice, the pellets were removed 6 hr prior to sacrificing. 3. The binding of [3H]MK-801 to membranes prepared from spinal cord and brain regions (cortex, pons-medulla, hypothalamus, hippocampus, amygdala, striatum, and midbrain) was determined by using a 5 nM concentration of the ligand in the presence of 30 microM glycine and 50 microM of glutamate. 4. In nonabstinent morphine-tolerant mice, the binding of [3H]MK-801 was decreased in pons-medulla and hypothalamus, but was increased in the spinal cord in comparison to that in placebo controls. The reduction in binding in pons-medulla was due to a decrease in the Bmax value; the Kd value remained unchanged. The binding of [3H]MK-801 was increased in the hippocampus of morphine-abstinent mice. 5. These studies demonstrate that NMDA receptors of brain regions and spinal cord are differentially affected in morphine-tolerant and abstinent mice.

1. The effect of NG-monomethyl-L-arginine (NMMA), an inhibitor of nitric oxide synthase (NOS), on the development of tolerance to and physical dependence on morphine was determined in the rat. 2. Male Sprague-Dawley rats were rendered tolerant to and dependent on morphine by the subcutaneous implantation of four morphine pellets (each containing 75 mg morphine base) during a 3 day period. Placebo pellet implanted rats served as controls. 3. Chronic administration of morphine resulted in the development of tolerance to the analgesic action of morphine. Twice daily injections of NMMA (4 or 8 mg/kg) attenuated the tolerance to morphine as evidenced by higher analgesic response in NMMA treated than in vehicle treated morphine tolerant rats. 4. Chronic administration of morphine also resulted in the development of physical dependence as evidenced by the appearance of a variety of symptoms including stereotyped jumping response following naltrexone injection. Concurrent treatment with NMMA inhibited naltrexone-induced jumping response but other responses like fecal boli formation, wet dog shakes, teeth chattering, rearing and ejaculations were not modified. 5. It is concluded that inhibition of NOS can attenuate the development of tolerance to, and physical dependence on, morphine in the rat. However, it appears that higher doses of NOS inhibitors are required in the rat than in the mouse for blockade of both tolerance and physical dependence processes.

1. The effect of dizocilpine (MK-801), a non-competitive inhibitor of N-methyl-D-aspartate (NMDA) receptor on the development of tolerance to the analgesic and hypothermic actions of U-50,488H, a highly selective kappa-opiate receptor agonist, was determined in the rat. 2. Male Sprague-Dawley rats were made tolerant to the pharmacological actions of U-50,488H by twice daily intraperitoneal (i.p.) injections of the drug (25 mg/kg) for 4 days. 3. Multiple injections of U-50,488H resulted in the development of tolerance to its analgesic and hypothermic actions in the rat. MK-801 injected 10 min before each injection of U-50,488H, dose-dependently inhibited the development of tolerance to the analgesic action but the tolerance to the hypothermic action of U-50,488H was unaffected. 4. Multiple injections of U-50,488H decreased the body weight gain. MK-801 dose-dependently decreased the gain in body weight further. 5. The results indicate that non-competitive antagonism of the NMDA receptor by MK-801 can selectively inhibit the tolerance to the analgesic action of U-50,488H in the rat, however, such an effect was associated with significant decreases in normal gain in body weight.

1. Abuse of the narcotic drug diacetylmorphine (heroin), as well as methadone, a drug for treating heroin addiction, has been associated with alterations in immune function in humans. The current study was performed to assess the direct (in vitro) immunomodulatory effect of exposure to these drugs, in view of the very limited studies reported thus far on this effect. 2. Murine splenocytes or peritoneal macrophages were cultured in vitro at concentrations of 0.0001-100 microM heroin or methadone. B-cell function was assessed by quantitating cellular proliferation in response to stimulation with an antigen analog; T-cell regulatory function was assessed by culturing splenocytes with or without drugs in the presence of anti-CD3 antibody and subsequently quantitating cytokine production; and T-cell effector function was evaluated by culturing lymphocytes with or without drugs during a 5-day induction culture followed by assessment of specific cytotoxic T-lymphocyte (CTL) activity. Natural immunity was assessed by quantitating basal and IL-2 augmented natural killer (NK) cell function, and macrophage function was assessed by cytokine production. 3. In vitro exposure to heroin resulted in decreased B-cell proliferation at concentrations of 1-100 microM, and methadone had a similar effect at concentrations of 0.1-100 microM. 4. Production of IL-2 was suppressed by 0.1-100 microM of heroin, whereas exposure to methadone appeared to result in a generalized modulation, with suppression of IL-2 at most concentrations. In contrast, IL-4 production was only affected at the 100 microM concentration of both drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

1. The effects of morphine tolerance and abstinence on the characteristics of N-methyl-D-aspartate (NMDA) receptors, labeled with [3H]MK-801, were determined in the brain regions and spinal cord of the rat. 2. Male Sprague-Dawley rats were rendered tolerant to and physically dependent on morphine by subcutaneous implantation of six morphine pellets during a 7-day period. In tolerant (non-abstinent) rats, the pellets were left intact at the time of sacrificing, whereas in the abstinent rats the pellets were removed 16 hr prior to sacrificing. 3. The binding of [3H]MK-801, an NMDA receptor antagonist, to membranes prepared from spinal cord and brain regions (cortex, striatum, amygdala, hippocampus, hypothalamus, midbrain and pons-medulla) was determined using 5 nM concentration of the ligand in the presence of 30 microM glycine and 50 microM of glutamate. 4. In non-abstinent morphine tolerant rats, the binding of [3H]MK-801 was decreased by 40 and 33% in the midbrain and spinal cord, respectively, in comparison with their placebo controls. In morphine abstinent rats, the binding of [3H]MK-801 was decreased by 42, 29 and 50% in hypothalamus, midbrain and spinal cord, respectively, in comparison with their placebo controls. The binding of [3H]MK-801 to other brain regions and spinal cord of morphine tolerant and abstinent rats did not differ from their respective placebo controls. 5. Thus, these studies demonstrate, for the first time, that in the presence of glutamate and glycine, NMDA receptors of selected brain regions and spinal cord are down-regulated in rats treated chronically with morphine.

Male Swiss-Webster mice were rendered tolerant to morphine by subcutaneous implantation of a morphine pellet, each containing 75 mg morphine base, for 3 days. Mice implanted with placebo pellets served as controls. A high degree of tolerance to the analgesic effect of morphine developed as evidenced by decreased analgesic response to various doses of morphine. delta 9-Tetrahydrocannabinol (5, 10 and 20 mg/kg i.p.) produced dose-dependent analgesic and hypothermic effects in mice implanted with placebo pellets. A significant decrease in the analgesic effects of tetrahydrocannabinol was observed in morphine-tolerant mice as compared to placebo controls. Mice were rendered tolerant to delta 9-tetrahydrocannabinol by injecting the drug (5, 10, or 20 mg/kg i.p.) twice daily for 4 days. Vehicle-injected mice served as controls. Tolerance to the analgesic and hypothermic effects of delta 9-tetrahydrocannabinol in mice injected chronically with the drug was evidenced by the decreases in the intensity of these responses when compared to those observed in vehicle-injected controls. Morphine produced dose-dependent analgesic and hypothermic effects in mice injected chronically with vehicle but the intensity of these effects was significantly lower in mice injected chronically with delta 9-tetrahydrocannabinol. These results indicate that a possible interaction exists between delta 9-tetrahydrocannabinol and the mu-opioid receptors and that a substantial tolerance to analgesic and hypothermic effects of morphine develops in delta 9-tetrahydrocannabinol-tolerant mice.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of the methyl esters of L-tyrosine (L-Tyr-OMe) and L-tryptophan (L-Trp-OMe) on the analgesic action of trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidin)cyclohexyl]-benzene acetamide methane sulfonate (U-50,488H), a kappa-opioid receptor agonist, were determined in male Swiss-Webster mice using the tail-flick test. Intraperitoneal injections of U-50,488H produced a dose-dependent analgesic response. The analgesic response to all doses of U-50,488H was potentiated by L-Tyr-OMe at 200 mg/kg injected intraperitoneally 30 min prior to the injection of U-50,488H. The effect of various doses of L-Tyr-OMe (50, 100 and 200 mg/kg) on the analgesia produced by 20 mg/kg of U-50,488H was also determined. The lowest dose (50 mg/kg) of L-Tyr-OMe did not modify U-50,488H-induced analgesia but the two higher doses enhanced it significantly. L-Tyr-OMe by itself at all the doses tested had no effect on the tail-flick latency. L-Trp-OMe (200 mg/kg) enhanced the analgesic action of 10 and 20 mg/kg doses of U-50,488H but not that induced by a 5 mg/kg dose. The analgesia induced by 20 mg/kg of U-50,488H was potentiated by L-Trp-OMe at 100 and 200 mg/kg but not by a 50 mg/kg dose. L-Trp-OMe by itself also did not alter the tail-flick latency. Previously, the studies in this laboratory have shown that L-Try-OMe potentiates morphine, a mu-opioid receptor agonist-induced analgesia.(ABSTRACT TRUNCATED AT 250 WORDS)

1. The effect of morphine tolerance and abstinence on the binding of [3H]naltrexone to discrete brain regions and spinal cord of the rat was determined. 2. Male Sprague-Dawley rats were implanted s.c. under light ether anesthesia with six morphine pellets for a 7-day period. Each pellet contained 75 mg of morphine base. Rats implanted with six placebo pellets each served as controls. 3. This procedure resulted in the development of tolerance to morphine as evidenced by decreased analgesic response to various doses of morphine. 4. The binding characteristics (Bmax or Kd values) of [3H]naltrexone, an opiate receptor antagonist, were determined in various tissues of morphine tolerant and abstinent rats. In the tolerant rats, the pellets were left in place at the time of sacrificing, whereas in the abstinent rats, the pellets were removed 18 hr prior to sacrificing. 5. The binding of [3H]naltrexone to opiate receptors on membranes prepared from brain regions (hypothalamus, hippocampus, cortex, pons and medulla, midbrain, corpus striatum and amygdala) and spinal cord of rats from various treatment groups was determined. 6. [3H]Naltrexone bound to tissue membranes at a single high affinity binding sites. The Bmax values of [3H]naltrexone to bind to opiate receptors on the membranes of amygdala and striatum were increased significantly in morphine tolerant rats when compared to the placebo controls, but the Kd values did not differ. 7. The Bmax and Kd values of [3H]naltrexone did not differ in any other brain region or spinal cord of morphine tolerant rats and their placebo controls. The binding constants of [3H]naltrexone were unaffected in morphine abstinent rats. 8. Previously we had shown that the binding of [3H]D-Ala2, MePhe4, Gly-ol5 enkephalin (DAMGO), a highly specific agonist for mu-opiate receptors was decreased in cortex, pons and medulla and spinal cord of morphine tolerant but not in the abstinent rats. In addition, delta and kappa receptors are unaffected in morphine tolerant and abstinent rats. 9. The results suggest that direction of change, as well as, the brain areas for mu-agonist and -antagonist opiate binding sites are affected differentially in morphine tolerant rats.

1. The effect of naltrexone pellets containing either 10 or 30 mg of naltrexone base on the development of tolerance and physical dependence on morphine was assessed in male Sprague-Dawley rats. Tolerance-dependence on morphine was induced by s.c. implantation of six morphine pellets, each containing 75 mg morphine base for 7 days. 2. Naltrexone pellet implantation blocked the development of tolerance to the analgesic and hyperthermic effects of morphine. Similarly, naltrexone pellet implantation reversed morphine withdrawal-induced body weight loss. The effect of pellets containing 10 and 30 mg naltrexone did not differ. 3. The effect of naltrexone (10 mg) pellet implantation on various signs of naltrexone-precipitated withdrawal such as body weight loss, hypothermia and increases in urinary and fecal output was investigated. Naltrexone pellet implantation did not alter the naltrexone-precipitated withdrawal-induced body weight loss. Concurrent naltrexone pellet implantation blocked the naltrexone-precipitated withdrawal-induced hypothermia, increased fecal and urinary output in morphine-dependent rats. 4. These results indicate that a single pellet of 10 mg of naltrexone can effectively block morphine tolerance and physical dependence in the rat. Such a procedure may be useful in studying biochemical, endocrinological and immunological mechanisms involved in opioid addiction processes.

1. The possible role of conformational requirements which fenfluramine and norfenfluramine must satisfy to elicit its observed pharmacological activities was investigated in mice with the use of four conformationally-rigid norfenfluramine analogues. 2. In this study, both the syn-9-amino and endo-2-amino isomers, which structurally resemble the gauche conformation of norfenfluramine, were found to have little or no effect on spontaneous locomotor activity. 3. On the other hand, the isomers (i.e. the anti-9-amino and exo-2-amino isomers) that mimic the anti conformation of norfenfluramine were capable of causing a decrease in spontaneous motor activity similar to that of norfenfluramine. 4. The analgesic activities of these rigid analogues were also assessed and all of the isomers were found to be weakly analgesic. 5. Only the exo-2-amino isomer exhibited analgesic potency similar to that of fenfluramine. Furthermore all of these compounds were capable of enhancing the analgesic activity of morphine.

1. The effects of naltrexone pellet implantation and removal on the analgesic and hypothermic effects of morphine and the binding of 3H-D-Ala2, MePhe4, Gly-ol5-enkephalin (DAMGO) to mu-opiate receptors in rat brain regions and spinal cord were determined. 2. Male Sprague-Dawley rats were implanted subcutaneously with a pellet containing 10 mg of naltrexone for 7 days. Placebo pellet implanted rats served as controls. The pellets were removed on day 8, and the analgesic and hyperthermic effects were determined in the rat 24 hr later. Morphine produced a dose-dependent analgesic and hyperthermic responses in rats implanted with placebo pellets. Enhanced analgesic and hyperthermic responses to morphine were produced in rats implanted with naltrexone pellets. 3. The binding constants (Bmax and Kd values) of [3H]DAMGO in regions of the brain (amygdala, hypothalamus, striatum, midbrain, hippocampus, pons + medulla and cortex), and spinal cord of rats with naltrexone pellet left intact or removed were determined. The Bmax values of [3H]DAMGO were increased in all brain regions and spinal cord of rats in which the naltrexone pellets were left in place or removed prior to sacrificing. However, the Kd values of [3H]DAMGO were unaffected by naltrexone treatment. 4. It is concluded that enhanced analgesic and hyperthermic response to morphine is produced in rats implanted with naltrexone pellets and such alterations in the pharmacological responses are due to up-regulation of mu-opiate receptors in all the brain regions and spinal cord. Additionally whether the pellets were left intact (receptors blocked) or removed (receptors not blocked), the mu-opiate receptors were up-regulated in spinal cord and all the regions of the brain.

The effect of U-50,488H, a kappa-opiate agonist, induced tolerance and abstinence on the characteristics of dopamine D2 receptors of brain regions and spinal cord was determined in the rat. Male Sprague-Dawley rats were injected with U-50,488H (25 mg/kg i.p) or its vehicle twice a day for 4 days. This procedure resulted in the development of tolerance to the analgesic activity of U-50,488H. The binding characteristics (Bmax and Kd values) of [3H]spiroperidol to dopamine D2 receptors were determined in discrete brain regions (hypothalamus, hippocampus, cortex, pons and medulla, midbrain, corpus striatum and amygdala) and spinal cord of U-50,488H-tolerant and -abstinent rats. Rats labeled as tolerant to U-50,488H were injected with U-50,488H on day 5 and killed 1 h later, whereas those labeled abstinent were killed on day 5 without the injection of the drug. Vehicle-injected rats served as controls. [3H]Spiroperidol bound to brain regions and spinal cord membranes at a single high affinity site. The Bmax and Kd values of [3H]spiroperidol in brain regions and spinal cord of U-50,488H-tolerant and abstinent rats did not differ from their respective vehicle-injected controls. The behavioral responses (total distance travelled, horizontal activity, movement time, total number of movements, number of stereotypic movements, stereotypic time and rest time) to different doses of a selective dopamine D2 receptor agonist, 2-bromo-alpha-ergocryptine (bromocriptine) were also determined in rats treated chronically with U-50,488H.(ABSTRACT TRUNCATED AT 250 WORDS)

1. The possible role of pharmacokinetics of morphine in the development of tolerance to the analgesic and hyperthermic effects of morphine was studied in the rat. 2. Male Sprague-Dawley rats were made tolerant to morphine by implanting 6 morphine pellets each containing 75 mg of morphine base for 7 days. The assessment of the degree of tolerance to morphine and pharmacokinetic parameters were done 72 hr after pellet removal. 3. Tolerance developed to both the analgesic and hyperthermic effects of morphine as evidenced by decreased responses to morphine in morphine pellet implanted rats compared with placebo pellet implanted rats. 4. The pharmacokinetic parameters, AUC0-->infinity, Cmax, t1/2, k, MRT, Vss and Clt were determined after injecting 5 and 10 mg/kg doses of morphine intravenously to placebo and morphine pellet implanted rats and using a highly sensitive and specific RIA method to quantitate serum levels of morphine. For a 5 mg/kg dose of morphine, the AUC0-->infinity and t1/2 in morphine pellet implanted rats were significantly higher than in placebo pellet implanted rats, but the k value was lower. The other pharmacokinetic parameters for morphine in the two treatment groups did not differ. For 10 mg/kg dose, the only change was an increase in the MRT in morphine tolerant rats when compared to nontolerant rats. 5. The results establish that the development of tolerance to the analgesic and hyperthermic effects of morphine is not related to pharmacokinetics of morphine in serum but may be related to modification of receptor systems in the central nervous system.

The effect of morphine tolerance-dependence and abstinence on the characteristics of delta-opiate receptors was determined in male Sprague-Dawley rats. Two ligands used for characterizing the receptors were [3H][D-Ser2,Thr6]leucine-enkephalin ([3H]DSTLE) and [3H][D-Pen2,D-Pen5]enkephalin ([3H]DPDPE). Rats were implanted s.c. under light ether anesthesia with six morphine pellets (each containing 75 mg of morphine free base). Rats which served as controls were implanted similarly with placebo pellets. Two sets of rats were used. In one group of rats, the pellets were left intact (tolerant-dependent) at the time of sacrificing and in the other the pellets had been removed 18 h earlier (abstinent). The spinal cord and brain regions (amygdala, hippocampus, hypothalamus, corpus striatum, mid-brain, pons and medulla and cortex) were dissected for binding studies. The binding of [3H]DSTLE to membranes of cerebral cortex of morphine-tolerant-dependent rats was decreased in comparison to control rats, and was due to a decrease in Bmax rather than Kd value. The binding of [3H]DSTLE to other brain regions or spinal cord of morphine-tolerant-dependent and abstinent rats did not differ from their respective controls. On the other hand, the binding of [3H]DPDPE was unaffected in any brain region or the spinal cord of morphine-tolerant-dependent and abstinent rats when compared to their controls. The decrease in binding of [3H]DSTLE to cortical membranes of morphine-tolerant-dependent rats amounted to 15%. Since DSTLE also binds to mu-opiate receptors, which have earlier been shown to be decreased in cortex of morphine-tolerant-dependent rats, and the binding of a more selective delta-opiate ligand [3H]DPDPE was unaffected, it is concluded that central delta-opiate receptors do not play a role in the development of morphine-induced tolerance-dependence or abstinence processes in the rat.

The effects of chronic administration of U-50,488H, a K-opiate receptor agonist, on the binding of [3H]ethylketocyclazocine ([3H]EKC) to K-opiate receptors on the cerebral cortical and spinal cord membranes of spontaneously hypertensive (SHR), Wistar-Kyoto normotensive (WKY), and Sprague-Dawley (SD) rats were determined. Age-matched (10 weeks old) male rats of each strain were injected twice daily for 7 days with either U-50,488H (25 mg/kg, i.p.) or its vehicle. On day 8, the rats were killed. The cerebral cortex and the spinal cord were isolated for binding studies. The systolic blood pressure and heart rate of SD and WKY rats did not differ but the blood pressure of SHR rats were higher than that of SD and WKY rats. The receptor density (Bmax) and apparent dissociation constant (Kd) values of [3H]EKC binding to the spinal cord of WKY and SHR rats did not differ. However, the spinal cord of SD rats had higher Bmax and Kd values than WKY or SHR rats. The cortex of the SD rats had a lower Bmax value than the other two strains. Treatment with U-50,488H decreased the Bmax value of [3H]EKC in spinal cord of SD rats, increased the Kd value in SHR rats, and had no effect in WKY rats. Decreases in the Bmax value were produced in the cortex of all strains of rats, but a greater effect was observed in WKY and SHR rats than in SD rats.

1. In order to determine whether the degree of tolerance to and physical dependence on morphine induced by pellet implantation procedure in the rat depends on the dose used and the kinetic parameters, the effect of implantation of different number of pellets on tolerance-dependence and elimination kinetics of morphine from serum was determined. 2. Male Sprague-Dawley rats were implanted subcutaneously with pellets. Each pellet contained 75 mg of morphine free base. Three schedules of implantation were used. They included 2 pellets during a 3-day period (2/3), 4 pellets during a 3-day period (4/3) and 6 pellets during a 7-day period (6/7). Placebo pellets which did not contain morphine were implanted in rats which served as controls. 3. The degree of tolerance to and physical dependence on morphine increased as the number of morphine pellets implanted increased. 4. In separate groups of rats implanted with pellets, elimination kinetics of morphine was studied using radioimmunoassay. The kinetic parameters were: area under serum morphine concentration time curve (AUC0----infinity), serum concentration of morphine extrapolated to time zero (Cmax), half-life (t1/2), elimination rate constant (k), mean residence time (MRT) and total body clearance (Clt). 5. The AUC0----infinity and Cmax increased in proportion to the number of pellets implanted. The t1/2, k, MRT and Clt values for 2/3 and 4/3 schedules did not differ, but for 6/7 schedule were significantly different from the other two schedules. The degree of tolerance to and physical dependence on morphine was directly related to the AUC0----infinity and Cmax. The longer t1/2 and MRT and lower Clt and k values in 6/7 schedule may reflect a saturation of glucuronic acid transferase, the main enzyme metabolizing morphine in the liver, and may account for the greater degree of tolerance and physical dependence.

1. Chronic administration of opiates to rodents results in the development of tolerance to their pharmacological effects. Physical dependence also develops and is shown by the appearance of abstinence syndrome. 2. Opiates produce their effects by acting on three types of opiate receptors, namely mu, delta and kappa. The qualitative and quantitative aspects of the tolerance-dependence and abstinence symptoms observed after chronic administration of agonists acting at mu-, delta- and kappa-opiate receptors appear to differ. 3. Tolerance-dependence on mu-opiate agonists, such as morphine, is associated with down-regulation of mu-opiate receptors in spinal cord and specific areas of the brain but delta- and kappa-opiate receptors are unchanged. During abstinence from mu-opiate agonists, brain and spinal cord mu-, delta- and kappa-opiate receptors are unaffected. 4. Chronic administration of kappa-opiate agonists, such as U-50,488H, results in the development of tolerance to its pharmacological effects and a mild degree of physical dependence. Such changes are associated not only with alterations of delta and kappa opiate receptors in brain and spinal cord, but also primarily with a down-regulation of kappa-opiate receptors in spinal cord and specific brain regions. mu-Opiate receptors are unaffected. 5. Chronic administration of delta-opiate agonists results in down-regulation of brain delta-opiate receptors. 6. It is concluded that tolerance-dependence on mu-, delta- and kappa-opiate receptors is associated with down-regulation of their own type of receptors in the spinal and supraspinal areas. Abstinence, on the other hand, does not alter brain and spinal cord opiate receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

1. The effect of intraperitoneal administration of Panax ginseng on the development of tolerance to the analgesic and hyperthermic actions of morphine was determined in male Sprague-Dawley rats. Rats were rendered tolerant to morphine to different degrees by the subcutaneous implantation of either four pellets of morphine over a 3-day period or six pellets over a 7-day period. Each pellet contained 75 mg of morphine free base. Rats serving as controls were implanted with placebo pellets. 2. Daily administration of ginseng extract (6.25-50.0 mg/kg) for 3 days inhibited the development of tolerance to the analgesic effect but not to the hyperthermic effect of morphine in the four pellet schedule. 3. In six pellet schedule, daily administration of ginseng extract (25 and 50 mg/kg) for 7 days also inhibited the development of tolerance to the analgesic effect of morphine, but the 100 mg/kg dose had no effect. On the other hand, in six pellet schedule, the administration of ginseng extract (50 and 100 mg/kg) once daily for 7 days inhibited the development of tolerance to the hyperthermic effect of morphine. 4. It is concluded that in appropriate doses, ginseng extract has inhibitory activity on the development of tolerance to the pharmacological actions of morphine.

1. The effect of intraperitoneal injections of U-50,488H, a kappa-opiate receptor agonist, on the development of tolerance to the analgesic and hyperthermic effects of morphine was determined in male Sprague-Dawley rats. 2. Tolerance was induced by implantation of four morphine pellets during a 3-day period (4/3 schedule) or six morphine pellets during a 7-day period (6/7 schedule). 3. Administration of U-50,488H (25 mg/kg, twice a day for 3 days in 4/3 schedule) or (5, 10 and 20 mg/kg twice a day for 7 days in 6/7 schedule) did not affect the development of tolerance to the pharmacological actions of morphine. 4. It is concluded that activation of kappa-opiate receptors does not modify the development of tolerance to morphine in the rat.

The effect of chronic administration of morphine and its withdrawal on the characteristics of mu-opiate receptors was determined in male Sprague-Dawley rats. The ligand used for characterizing the receptors was [3H][D-Ala2,MePhe4,Gly5-ol]enkephalin ([3H]DAMGO). Rats were implanted s.c. under light ether anesthesia with six morphine pellets (each containing 75 mg of morphine free base). Rats serving as controls were implanted similarly with placebo pellets. Two sets of animals were used. In one group of rats, the pellets were left intact (tolerant-dependent) at the time of killing and in the other the pellets had been removed 18 h earlier (abstinent). The spinal cord and brain regions (amygdala, hippocampus, hypothalamus, corpus striatum, midbrain, pons and medulla, and cortex) were dissected. In morphine-abstinent rats, the binding of ligands of mu-opiate receptors to membranes of spinal cord and brain regions did not change. In non-abstinent morphine-tolerant-dependent rats, the binding of [3H]DAMGO to membranes of spinal cord, pons and medulla, and cerebral cortex was found to be decreased. These changes were due to decreases in the Bmax values rather than Kd values for the binding of [3H]DAMGO. The results clearly indicate that morphine-induced tolerance-dependence in the rat is associated with changes in the selected brain regions and spinal cord with mu-opiate receptors being down-regulated in spinal cord, pons and medulla, and cerebral cortex. It is concluded that tolerance to morphine in the rats may be due to down-regulation of central mu-opiate receptors. However, mu-opiate receptors are unaffected in morphine abstinence.

The effects of morphine tolerance-dependence and abstinence on 5-HT1A receptors in brain regions and spinal cord of the rat were determined. Tolerance to and physical dependence on morphine was induced in male Sprague-Dawley rats by implanting six morphine pellets (each containing 75 mg of morphine free base) during a seven day period. Two groups of rats were used for binding studies. In one group the pellets were left intact (tolerant-dependent) and in the other they were removed (abstinent). Rats were killed, and spinal cords and brains were excised. Brain was dissected into seven regions (amygdala, hippocampus, hypothalamus, striatum, midbrain, pons + medulla and cortex). 5-HT1A receptors were characterized by using [3H]8-hydroxy-di-n-propylaminotetralin [( 3H]DPAT) as the ligand and unlabelled 5-HT to determine the non-specific binding. In morphine and placebo tolerant-dependent rats the binding of [3H]DPAT to 5-HT1A receptors in brain regions and spinal cord did not differ. The Bmax value of [3H]DPAT in the hypothalamus of morphine abstinent rats was decreased by 61.9%. No change in Bmax value was observed in other brain regions and spinal cord. The Kd values were unaffected. Subcutaneous administration of DPAT produced hypothermia in rats from which pellets had been removed. The intensity of DPAT-induced hypothermic response was greater in morphine abstinent rats as compared to placebo abstinent rats. Since DPAT is believed to have a major action on the presynaptic 5-HT neurons, it is concluded that in morphine abstinent rats 5-HT1A receptors are down-regulated in hypothalamus, but in morphine tolerant-dependent rats they are unaffected.

1. The effects of intraperitoneal administration of a standard extract of Panax ginseng alone and in combination with morphine were determined in male Sprague-Dawley rats. 2. Ginseng extract at 200 mg/kg produced analgesia and hypothermia. These effects of ginseng were not reversed by naltrexone. 3. A dose of morphine (8 mg/kg) produced analgesia and hyperthermia. The analgesic response to morphine was antagonized by 25 and 50 mg/kg doses of ginseng but not by 12.5, 100 and 200 mg/kg doses. 4. Morphine-induced hyperthermia was antagonized by 12.5-200 mg/kg doses of ginseng. 5. Administration of morphine (50 mg/kg) produced cataleptic effect which was antagonized by 25 mg/kg of ginseng. 6. The results suggest that ginseng extract at high doses produces analgesia and hypothermia in the rat by a non-opiate mechanism, and antagonizes the acute pharmacological effects of morphine.

The influence of thyrotropin releasing hormone (TRH) and its postulated metabolite histidyl-proline diketopiperazine (HPD) on sedation and analgesia produced by delta 9-tetrahydrocannabinol (THC) was investigated in mice. Intracerebral administration of HPD (10 microgram) by itself decreased motor activity, whereas, TRH (10 microgram) was without any effect. THC (10 and 20 mg/kg) given i.p. decreased the motor activity and this effect was antagonised by prior treatment with TRH or HPD. Administration of THC produced analgesia as evidenced by delay in the tail-flick reaction time to a thermal stimulus. Pretreatment with TRH or HPD also antagonized the THC-induced analgesia. THC-induced analgesia was not modified by s.c. pretreatment with naloxone, an opiate antagonist. TRH or HPD pretreatment had no effect on the distribution of total radioactivity representing THC and its metabolites in brain and plasma. These studies indicate that TRH and HPD can antagonize THC-induced sedation and analgesia and that HPD may be an active metabolite of TRH. These effects were observed without altering the distribution of the drug and metabolite in brain and plasma, and therefore their effect may involve their direct actions on the central nervous system. Finally THC induced analgesia does not seem to involve opiate receptors and their involvement in the mechanism by which TRH or HPD antagonize THC-induced analgesia is unlikely.

The effects of various doses of 1-trans-delta9-tetrahydrocannabinol (delta9-THC) on naloxone-induced withdrawal were studied in mice rendered dependent on morphine by the pellet implantation procedure. When administered i.p., 30 min prior to naloxone, delta9-THC, inhibited the naloxone-induced withdrawal jumping response. Two other signs of morphine withdrawal (defecation and rearing behavior) were also suppressed by deltapTHC. It is suggested that delta9-THC or some of its derivatives may have potential use in narcotic detoxification.

Tolerance to and physical dependence on morphine in the rat was induced by injecting increasing doses of morphine sulfate (M.S.) administered i.p. twice daily for 14 days. The last dose of M.S. was 200 mg/kg. This procedure produced a 4-fold tolerance to morphine as evidence by the increased dose of morphine required to produce analgesia. The degree of dependence was quantified by determining the naloxone ED50 for the stereotyped withdrawal jumping response. Body weight loss and hypothermic responses during abrupt and naloxone-induced withdrawal were also measured. The degree of tolerance and dependence produced by multiple injection procedure was comparable to that produced by 2 pellets containing 75 mg of morphine base implanted for 3 days. The level and turnover of brain serotonin, determined 6 or 12 h after the last morphine sulfate injection did not differ significantly from that of saline injected control animals. These data indicate that multiple injection technique produces a mild degree of tolerance to, and physical dependence on, morphine which was not related to changes in brain serotonin level or turnover.

A stability-indicating reversed-phase high-performance liquid chromatographic method for the determination of the topical anaesthetic dicyclonine hydrochloride in various oral spray and gel formulations is described.

The effects of melanotrophin release inhibiting factor (Pro-Leu-Gly-NH2, MIF), its possible metabolites, Pro-Leu-OH, Leu-Gly-NH2, Leu-Gly-OH and an analogue, cyclo(Leu-Gly), on [3H]spiroperidol binding sites in the striatum and on [3H]apomorphine binding sites in the striatum and hypothalamus of male Sprague-Dawley rats were determined. [3H]Spiroperidol binding to dopamine receptors in striatal membranes was unaffected by any of the above peptides in concentration up to 0.1 mM. The binding of [3H]apomorphine was enhanced by MIF, Pro-Leu-OH and cyclo(Leu-Gly) in both striatal and hypothalamic membranes in submicromolar concentrations. Leu-Gly-NH2 and Leu-Gly-OH did not affect [3H]apomorphine binding to dopamine receptors in striatum of hypothalamus. The enhancement in binding of [3H]apomorphine by MIF and cyclo(Leu-Gly) was not related to the changes in the number of binding sites but to an increase in the affinity to the receptors. The results indicate that MIF and some of its related peptides do not affect dopamine receptor binding sites labeled by the neuroleptic [3H]spiroperidol but facilitate the transmission in those sites labeled by [3H]apomorphine. Since [3H]apomorphine and [3H]spiroperidol predominantly label pre- and post-synaptic dopamine receptors, it is concluded that MIF and its active analogs interact with presynaptic dopamine receptors.

The effect of TRH and its analogs, MK771 and RX-77368 on the binding of [3H]D-serine-6-threonine-leucine enkephalin (delta opiate receptors), [3H]ethylketocyclazocine (kappa receptors) and [3H]naltrexone (mu receptors) to the rat brain membranes was determined. Neither TRH nor its analogs affected the binding of ligands for mu, delta, and kappa opiate receptors at either 35 or 0 degrees C. Since previous studies from this laboratory indicate that the drugs acting at the kappa, and delta opiate receptors inhibit the binding of [3H](3-MeHis2) TRH to brain TRH receptors, the present studies suggest a unidirectional interaction between opiates and TRH in the brain at the level of their receptors.

The interactions of thyrotropin releasing hormone, its metabolites and synthetic analogues with acute and chronic effects of endogenous and exogenous opiates have been described. The endogenous and exogenous opiates are represented by beta-endorphin and morphine, respectively. The pharmacological effects of opiates include analgesia, temperature effects, respiratory depression, catalepsy, locomotor activity, opiate receptor binding, tolerance, and physical dependence. Thyrotropin releasing hormone and related compounds appear to (a) antagonize hypothermia, respiratory depression, locomotor depression and catalepsy but not the analgesia induced by opiates, (b) inhibit the development of tolerance to the analgesic effect but not to the hypothermic effect of opiates, (c) inhibit the development of physical dependence on opiates as evidenced by the inhibition of development of certain withdrawal symptoms, and (d) suppress the abstinence syndrome in opiate dependent rodents. Thyrotropin releasing hormone does not interact with the opiate receptors in the brain. Potential therapeutic applications of thyrotropin releasing hormone and its synthetic analogues in counteracting some of the undesirable effects of opiates are discussed.

The effects of three kappa opioid agonists namely, bremazocine, tifluadom and U-50,488H were studied on blood pressure and heart rate in urethane-anesthetized normal and bilateral adrenal demedullated rats. Bremazocine (0.2, 0.4 and 0.6 mg/kg i.v.) produced a dose-dependent decrease in heart rate, while only 0.4 mg/kg bremazocine produced marked hypotension. The effect appeared to be long lasting because even at 60 min following drug administration the decreases in both heart rate and blood pressure continued. Bilateral adrenal demedullation did not change bremazocine-induced fall in blood pressure but the bradycardia was partially blocked. Tifluadom (0.1-0.4 mg/kg i.v.) produced an initial arrest of heart beat followed by bradycardia which recovered in about 60 min. Except for a very transient fall soon after drug administration no significant effect was observed on blood pressure. In adrenal demedullated rats, tifluadom induced initial arrest of heart was not affected but the subsequent bradycardia was blocked. U-50,488H (0.2, 0.4 and 0.6 mg/kg i.v.) produced dose-dependent bradycardia and hypotension both of which were blocked following bilateral adrenal demedullation. Naltrexone methylbromide (MRZ 2663 BR), a quaternary opioid antagonist, injected 5 min prior to U-50,488H, blocked its cardiovascular effects. The results suggest that kappa opioid agonists given i.v. depress cardiovascular system and these effects are mediated through the adrenal medulla and peripheral opioid receptors. The differential effects of kappa opioid agonists on blood pressure and heart rate suggest that either the three kappa agents interact differentially at the kappa opioid receptors or the subtypes of receptors for the kappa opioid exist.

The subcutaneous administration of buprenorphine to male Sprague-Dawley rats produced a dose-dependent analgesia and hyperthermia in a dose range of 0.25-2 mg/kg. The subcutaneous administration of buprenorphine (0.5 mg/kg) twice a day for 4 days resulted in the development of tolerance to its analgesic and hyperthermic actions. Daily administration of melanotropin release inhibiting factor (Pro-Leu-Gly-NH2) or cyclo (Leu-Gly) (2 mg/kg s.c.) for 4 days, inhibited the development of tolerance to buprenorphine, as evidenced by greater analgesic and hyperthermic responses to buprenorphine in peptide-treated than in vehicle-treated buprenorphine-tolerant rats. The repeated injections of peptides did not alter the analgesic or the hyperthermic response to buprenorphine in non-tolerant rats. These studies suggest the possible role of hypothalamic peptides in blocking the development of tolerance to the pharmacological effects of buprenorphine, a potent analgesic agent.

A single i.p. injection of naltrexone (20 mg/kg) partially inhibited the development of physical dependence upon morphine in mice rendered dependent on morphine by implantation of a pellet containing 75 mg of morphine free base for three days. This was evidenced by an increase in the dose of naloxone (ED50) required to precipitate withdrawal jumping response. The increase in naloxone ED50 was much more pronounced when naltrexone was given prior to and during the course of pellet implantation. Inhibition was also observed when naltrexone was administered one day after the morphine pellet implantation, i.e., after some dependence had already developed. Naltrexone administration prior to and during the development of dependence also inhibited, but only partially, the loss of body weight and hypothermic response observed during abrupt withdrawal of morphine in morphine-dependent mice. The inhibitory effect of naltrexone on morphine dependence development was not associated with changes in brain morphine concentration.

1. The influence of diets differing in protein concentration on the characteristics of mu, delta, and kappa-opiate receptors and on the analgesic and hyperthermic responses to morphine was examined in rats. Three groups of male Sprague-Dawley rats were maintained for four weeks on isocaloric diet containing either 4, 20 or 50% protein. 2. The animals maintained on 4% protein diet weighed 92 +/- 2% of the initial weight at the end of the fourth week, whereas animals maintained on 20% and 50% protein diet weighed 222 +/- 2% and 221 +/- 2%, respectively. The average food intake per 100 g body weight on day 1 of the study in 4, 20 and 50% protein diet group was 5.0 +/- 2.2 g, 10.4 +/- 1.4 g, and 10.0 +/- 1.2 g, respectively. This difference in food intake was not observed during rest of the period of the study. 3. Water intake was higher for the animals maintained on diet containing 50% protein as compared to the other two groups. 4. The analgesic and the hyperthermic response to morphine varied in direct relation to the concentration of protein in the diet. The concentration of morphine in the brain and plasma of animals maintained on the three diets following challenge dose of morphine did not differ. Similarly the Bmax and Kd values for the binding of [3H]naltrexone, [3H]D-Ser2-Thr6-leucine enkephalin and [3H]ethylketocyclazocine to brain membranes prepared from rats kept on 4, 20 and 50% protein concentration did not differ. 5. It is concluded that the diet differing in protein concentration can alter the responses to morphine, and that such altered effects can not be accounted for by the changes in the distribution of morphine in brain and plasma or to the changes in the characteristics of the mu, delta and kappa opiate receptors in the brain.

Spontaneously hypertensive rats were found to have a greater density of specific [3H]spiroperidol binding sites in the corpus striatum and hypothalamus when compared to the normotensive Wistar-Kyoto rats. The apparent dissociation constant (Kd) for [3H]spiroperidol binding in the two groups of rats did not differ. Chronic administration of cyclo(leucyl-glycine), an analog derived from the hypothalamic peptide, melanotropin release inhibiting factor, decreased the enhanced number of [3H]spiroperidol binding sites in the striatum and hypothalamus of the hypertensive rats. These results further suggest that cyclo(leucyl-glycine) interacts with brain dopamine receptors, and that brain dopamine receptors may be involved in the etiology of hypertension.