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PubMed1991

Acute and chronic morphine administration: effects of mixed-action opioids in rats and squirrel monkeys responding under a schedule of food presentation.

The effects of several opioid compounds were examined in rats and squirrel monkeys responding under a fixed-ratio 30 schedule of food presentation. In rats, dose-effect curves were determined before and after acute pretreatment with 5.6 mg/kg of morphine 5 to 6 hr before the session, as well as during and after the termination of a chronic regimen in which rats received 30.0 mg/kg/day of morphine. In monkeys, dose-effect curves were determined before, during and after the termination of a chronic regimen in which monkeys received 6.0 mg/kg/day of morphine. In morphine-pretreated rats, dose-effect curves for the opioid antagonists naloxone, naltrexone and diprenorphine shifted to the left of those determined when rats were not morphine-pretreated; whereas those for the mu-opioid agonists morphine and I-methadone and mixed-action opioids nalorphine, nalbuphine, butorphanol, pentazocine and bremazocine were unaltered. During chronic morphine administration in rats, dose-effect curves for morphine and butorphanol shifted to the right; whereas the dose-effect curves for naloxone and nalorphine shifted to the left of those determined when rats were not treated with morphine. The effects of pentazocine, nalbuphine, bremazocine and the kappa-opioid agonist U50,488 were unaltered in morphine-maintained rats. In morphine-maintained monkeys, the dose-effect curves for morphine and I-methadone shifted to the right; whereas those for naloxone, nalorphine and nalbuphine shifted to the left of the prechronic dose-effect curves. Dose-effect curves for butorphanol, pentazocine and U50,488 were unaltered. Overall, these results suggest that the chronic morphine administration procedure can be used to distinguish opioid compounds based upon their relative mu agonist and antagonist activity.

Animals↗
PubMed1994

Kappa agonist and antagonist properties of mixed action opioids in a pigeon drug discrimination procedure.

Previous investigations indicate that mixed action opioids (i.e., opioids with activity at a combination of opioid receptor sites or a combination of opioid and nonopioid sites) often possess kappa-like stimulus effects in the rat and monkey, but mu-like stimulus effects in pigeons. In the present investigation, the kappa agonist and antagonist actions of a series of mixed action opioids were examined in pigeons trained to discriminate a 0.017-mg/kg dose of the kappa agonist bremazocine from saline. The mixed-action opioids (-)-n-allylnormetazocine, (-)-cyclazocine, (-)-metazocine, levallorphan, buprenorphine, nalbuphine, butorphanol and nalorphine failed to substitute for the bremazocine stimulus. When administered in combination with the training dose of bremazocine, each of these opioids produced a dose-related antagonism of the bremazocine stimulus. With the exceptions of butorphanol and (-)-metazocine, the antagonist effects of these opioids were surmountable. Buprenorphine, (-)-n-allylnormetazocine and levallorphan produced their kappa antagonist effects at doses approximately 2 to 3 log units lower than those that decreased rates of responding when these opioids were administered alone, whereas approximately 1 log unit separated the kappa antagonist and rate-decreasing effects of nalorphine, nalbuphine and (-)-cyclazocine. In contrast, the kappa antagonist effects of butorphanol and (-)-metazocine were observed only at doses of markedly decreased response rates. A somewhat different profile was obtained with ethylketocyclazocine and ketocyclazocine in that these mixed action opioids produced partial substitution for and partial antagonism of the bremazocine stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

Effects of additional premedication on romifidine and ketamine anaesthesia in horses.

The clinical and cardiorespiratory effects of premedication with acepromazine, butorphanol or diazepam in addition to romifidine before induction of anaesthesia with ketamine were studied in 6 horses on 4 random occasions. Administration of romifidine alone or in combination with butorphanol resulted in an increase in arterial blood pressure, accompanied by a significant decrease in heart rate with second-degree atrio-ventricular heart block. Induction of anaesthesia with ketamine returned the heart rate to baseline value, but the arterial blood pressure was significantly increased compared to baseline. Including acepromazine in the premedication prevented the hypertension and bradycardia induced by romifidine. The respiratory rate was slightly decreased after premedication in all groups, but returned to the baseline value after induction of anaesthesia. Mild hypercapnia and significant hypoxaemia were observed during sedation and anaesthesia, reflecting an impairment of pulmonary function. Premedication with acepromazine before sedation with romifidine resulted in a fast induction and good anaesthesia. Inclusion of butorphanol in the premedication resulted in individual variation in the quality of induction and anaesthesia. Addition of diazepam to the sedation with romifidine resulted in good muscle relaxation with a smooth induction and maintenance of anaesthesia and an increased time before the horses responded to noxious stimuli, compared with romifidine and ketamine anaesthesia. All horses reached a standing position at the first attempt, but horses premedicated with diazepam in combination with romifidine showed mild ataxia after recovery.

Acepromazine↗
PubMed1995

Continuous epidural morphine/butorphanol infusion following selective dorsal rhizotomy in children.

The authors prospectively evaluated 15 patients who had undergone selective dorsal rhizotomy who were given a continuous morphine/butorphanol infusion, to determine whether variations in the postoperative pain control and side effects seen using a bolus technique could be reduced. Patients had an epidural catheter placed at the end of the operative procedure through which 50-60 micrograms/kg preservative-free morphine and 15-20 micrograms/kg butorphanol was administered. A continuous epidural infusion of 5 micrograms/kg h morphine and 1.2 micrograms/kg h butorphanol was then initiated. Postoperatively, mean pain scores were excellent. No patient required additional systemic analgesics during the 72-h investigational period. A low incidence of nausea, and no vomiting, pruritus, or respiratory depression was reported by the cohort. All patients maintained oxygen saturations above 95%. This indicates that the use of a continuous epidural infusion provides excellent pain control, decreases the occurrence of untoward side effects, and allows the early initiation of occupational and physical therapy postoperatively.

Analgesics↗
PubMed1981

Differential effects of opiate agonists-antagonists on morphine-induced hyperexcitability and analgesia in mice.

The effects of two opiate agonists-antagonists, butorphanol (4.0 and 8.0 mg/kg) and buprenorphine (0.1 and 1.0 mg/kg), were assessed on locomotor activity and analgesia in DBA/2 and C57BL/6 mice. Different behavioral effects were evident in these strains, which might be characterized by different reactions to the effects of opiates and by differences in endorphin distributions and opiate receptor populations. In particular, buprenorphine acted as an agonist-antagonist to morphine in both strains while a dissociation of butorphanol effects was evident, depending on the strain considered. The clinical implications of these findings are discussed.

Analgesia↗
PubMed1989

A comparison of the incidence of pruritus following epidural opioid administration in the parturient.

Epidural morphine is associated with a high incidence of pruritus when used for pain control in the post-Caesarean section population. The purpose of this study was to compare the incidence of pruritus associated with epidural morphine, fentanyl, buprenorphine and butorphanol. Sixty healthy Caesarean section patients were studied in a double-blind randomized fashion. Patients were questioned at 1, 3, 12 and 24 hours postpartum for the incidence of pruritus. This study demonstrated that the incidence of pruritus was significantly higher following the use of epidural morphine and fentanyl. Even though epidural butorphanol and buprenorphine exhibited a low incidence of pruritus, their duration of analgesia was not long enough to make either attractive for single-dose administration.

Adult↗
PubMed2000

Sex-related differences in the antinociceptive effects of opioids: importance of rat genotype, nociceptive stimulus intensity, and efficacy at the mu opioid receptor.

RATIONALE: Recent studies indicate that morphine is more potent as an antinociceptive agent in male than female rodents and monkeys. OBJECTIVES: To evaluate the influence of sex, nociceptive stimulus intensity and an opioid's relative efficacy on opioid-induced antinociception in rat strains (F344 and Lewis) that display differential sensitivity to morphine antinociception. METHODS: Antinociceptive testing was conducted using a rat warm-water (50-56 degrees C) tail-withdrawal procedure. Dose-response and time-course determinations were performed with various opioids. RESULTS: Across the nociceptive stimulus intensities tested, the high-efficacy mu opioids morphine, etorphine, and levorphanol were equally effective in males and females, but on average 2.5-fold more potent in males. At moderate stimulus intensities, the low-efficacy mu opioid buprenorphine was approximately 0.4-fold more potent in males, and at higher stimulus intensities more potent and effective (greater maximal effect) in males. At low stimulus intensities, the low-efficacy mu opioid dezocine and the mu/kappa opioid butorphanol were greater than 8.9-fold more potent in males, and at moderate stimulus intensities were more potent and effective in males. At a low stimulus intensity, the mu/kappa opioid nalbuphine was more potent and effective in males. At stimulus intensities in which buprenorphine, dezocine, butorphanol, and nalbuphine produced maximal effects in males but not females, these opioids antagonized the effects of morphine in females. Genotype-related differences were noted as opioids were generally more potent in F344 than Lewis males, whereas no consistent differences were observed between F344 and Lewis females. CONCLUSIONS: That sex differences in the potency and effectiveness of opioids increased with decreases in the opioid's relative efficacy and with increases in the nociceptive stimulus intensity suggests that the relative efficacy of mu opioids as antinociceptive agents is greater in male than female rats.

Analgesics, Opioid↗
PubMed1997

Discriminative stimulus effects of buprenorphine in the rat.

Buprenorphine, a potent "low efficacy" or "partial" morphine-like opioid agonist, has morphine-like discriminative effects in animals and humans discriminating morphine or a related drug. The purpose of the present study was to characterize further the discriminative effects of buprenorphine in subjects trained to discriminate buprenorphine itself. Rats trained to discriminate between SC injections of saline and either 0.03 or 0.1 mg/kg buprenorphine generalized completely to morphine and to other morphine-like agonists. These drugs were approximately 3 times more potent in the rats trained with 0.03 mg/kg buprenorphine than in those trained with 0.1 mg/kg; however, the potency of buprenorphine itself did not differ significantly between groups. Indicative of efficacy differences among mixed-action opioids, rats discriminating 0.03 mg/kg buprenorphine generalized completely to butorphanol and pentazocine and partially to nalbuphine, whereas those discriminating 0.1 mg/kg generalized completely to butorphanol, partially to pentazocine, and little to nalbuphine. Stimulus control of behavior by 0.1 mg/kg buprenorphine was blocked surmountably by low doses of antagonists, stereoselective, and pharmacologically selective. These results are consistent with those of other studies showing that the discriminative effects of buprenorphine are morphine-like and mediated by the mu-opioid receptor, and extend the conditions under which this has been demonstrated to stimulus control maintained by buprenorphine itself.

Animals↗
PubMed2001

Effects of gonadal steroid hormone treatments on opioid antinociception in ovariectomized rhesus monkeys.

RATIONALE: Gonadal steroid hormones altered opioid antinociception under some conditions in rodents, and we reported previously that chronic estradiol enhanced kappa but not mu opioid antinociception in ovariectomized rhesus monkeys. Sex differences have also been observed in the antinociceptive effects of opioid agonists. These findings suggest that gonadal hormones may modulate opioid antinociception. OBJECTIVES: To extend our previous studies of estradiol by examining the effects of progesterone alone, estradiol in combination with progesterone, and testosterone alone on opioid antinociception in ovariectomized rhesus monkeys. METHODS: Opioid effects were studied during chronic treatment with vehicle (sesame oil) or with progesterone alone (P; 0.32 mg/kg per day), a combination of progesterone+estradiol (P+E; 0.32 mg/kg per day P + 0.002 mg/kg per day E), or testosterone alone (T; 0.32 mg/kg per day). Opioid antinociception in a warm-water tail-withdrawal procedure was examined with the selective kappa opioid agonist U50,488, the selective mu agonist morphine, and the two mixed-action opioids butorphanol and nalbuphine. RESULTS: The steroid treatment regimens produced physiological levels of progesterone and estradiol similar to peak levels observed during the luteal phase of the menstrual cycle and physiological levels of testosterone similar to those observed in intact males. Treatment with P, P+E, or T did not alter baseline thermal nociception. P+E significantly increased the potency of U50,488 at 50 degrees C but not at 54 degrees C. Gonadal hormone treatments had little or no effect on antinociception produced by morphine, butorphanol, or nalbuphine at either temperature. CONCLUSIONS: These findings further suggest that chronic treatment with physiological levels of gonadal hormones may modulate the antinociceptive effects of U50,488 in ovariectomized rhesus monkeys.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1996

Inhibitory effects of diltiazem, an L-type Ca2+ channel blocker, on naloxone-increased glutamate levels in the locus coeruleus of opioid-dependent rats.

To investigate the effects of diltiazem, an L-type Ca2+ channel blocker, on naloxone-precipitated withdrawal and elevations of glutamate levels in the locus coeruleus (LC) of opioid-dependent rats, animals were continuously infused with 26 nmol/microliter/h of morphine or butorphanol intracerebroventricularly (i.c.v.) via osmotic minipumps for 3 days. I.c.v. injection of naloxone (an opioid-receptor antagonist, 48 nmol/5 microliters) precipitated withdrawal signs and increased extracellular fluid levels of glutamate in the LC of morphine- or butorphanol-dependent rats measured by in vivo microdialysis. Meanwhile, concomitant infusion of opioids with diltiazem (10 or 100 nmol/microliter/h) inhibited the withdrawal signs and prevented the elevations of glutamate levels in the LC. These results suggest that an expeditious release of glutamate in the LC region regulated by L-type Ca2+ channels mediated system plays a role in the expression of withdrawal signs from opioids.

Animals↗
PubMed1983

The effects of aging on opioid modulation of feeding in rats.

Feeding responses to naloxone and butorphanol tartrate were measured in Fisher-344 rats with ages of 2, 12, 22 and 28 months. The two younger groups were 10-100 times more sensitive than the older groups to the suppressive effects of naloxone on feeding. Additionally, the older rats were less responsive to the feeding enhancement following butorphanol injections. These results are consistent with reports of age-related changes in endogenous opioid systems.

Aging↗
PubMed1987

Opioid modulation of ingestive behaviors in the spiny mouse (Acomys cahirinus).

Feeding and drinking behavior were studied in deprived or sated spiny mice (Acomys cahirinus) at various time intervals following peripheral administration of naloxone hydrochloride and butorphanol tartrate. Naloxone attenuated both food and water intake, but not latency to respond, indicating existence of functional opioid-sensitive feeding and drinking systems in this species. Butorphanol tartrate, a mixed opioid agonist/antagonist produced a dose-related enhancement or suppression of feeding, the former naloxone reversible, but had no measureable effect on drinking.

Animals↗
PubMed1989

Synthetic opioids compared with morphine and ketamine: catalepsy, cross-tolerance and interactions in the rat.

Previously it has been shown in rats that both ketamine and morphine induced analgesia and, at larger doses, catalepsy and loss of the righting reflex, all of which were reversed by naloxone at widely different doses. Tolerance developed rapidly to either ketamine or morphine and there was cross-tolerance from ketamine to morphine. However, morphine potentiated the cataleptic effect of ketamine, whether fully-effective doses of morphine were given before ketamine or subeffective doses of both were given concurrently. The present study extends these observations to three specific mu-receptor agonists (sufentanil, fentanyl and alfentanil) and two mu- and kappa-agonist, mu-antagonist opioids (nalbuphine and butorphanol). All five of these opioids potentiated the cataleptic effect of ketamine. Each of the three specific mu agonists showed rapid development of tolerance. Fentanyl and alfentanil showed mutual cross-tolerance with ketamine, but sufentanil did not. This lack of sufentanil-ketamine cross-tolerance may reflect separation of the sites of agonist action and the sites of development of tolerance for the opioids and for ketamine. The potentiating effects of nalbuphine and butorphanol suggest that they potentiate ketamine-induced catalepsy, either by kappa-receptor interactions or by a mu agonist effect. It is suggested that the cataleptic effect of a combination of individually-subeffective doses of ketamine and morphine, rather than ketamine and one of the synthetic opioids, might be of more potential clinical usefulness.

Animals↗
PubMed1984

Opiate induced feeding is not dependent on the hippocampus.

It has been shown that spreading depression of the hippocampus can elicit feeding, and that several opioid peptides elicit spreading depression when injected into the hippocampus. To determine whether such depression is the primary mechanism by which opiates induce feeding, we tested the feeding effects of naloxone, an opiate antagonist, and butorphanol tartrate, a kappa-sigma agonist, on feeding in rats with and without hippocampal lesions. Naloxone tended to reduce intake approximately equally in the two groups. Similarly, the doses of butorphanol that increased intake in sham rats were equally effective in lesioned rats. It was concluded that the hippocampus is not the major structure mediating opiate-induced feeding.

Animals↗
PubMed1992

Taste responses and preferences for sweet high-fat foods: evidence for opioid involvement.

Preferences and cravings for sweet high-fat foods observed among obese and bulimic patients may involve the endogenous opioid peptide system. The opioid antagonist naloxone, opioid agonist butorphanol, and saline placebo were administered by intravenous infusion to 14 female binge eaters and 12 normal-weight controls. Eight of the binge eaters were obese. During infusion, the subjects tasted 20 sugar/fat mixtures and were allowed to select and consume snack foods of varying sugar and fat content. Naloxone reduced taste preferences relative to baseline in both binge eaters and controls. Total caloric intake from snacks was significantly reduced by naloxone in binge eaters but not in controls. This reduction was most pronounced for sweet high-fat foods such as cookies or chocolate. No consistent effects on taste preferences or food intakes were observed with butorphanol. Endogenous opioid peptides may be involved in mediating taste responses and preferences for palatable foods, notably those rich in sugar and fat.

Adolescent↗
PubMed1991

An animal model of bulimia nervosa: opioid sensitivity to fasting episodes.

A group of female rats was deprived and maintained at 75-80% of body weight at three different times during development. Following recovery to normal weight, food intake was measured with and without butorphanol tartrate, a kappa-sigma agonist, 8 mg/kg SC. Animals with a history of deprivation (DEP) showed an increase in postrecovery feeding when they were tested at normal body weight and not food deprived. More importantly, butorphanol prolonged food intake in the 3-h eating test only in the rats with a developmental history of food restriction. A developmental history of fasting in eating disorders may trigger changes in opiate systems that result in atypical feeding behavior in the adult.

Animals↗
PubMed1984

Physical dependence induced by opiate partial agonists in the rat.

The ability of four opiate partial agonists (buprenorphine, xorphanol, nalbuphine and butorphanol) to produce antinociception and morphine-like physical dependence was examined in the rat. For comparative purposes, morphine was also tested. Dose-response curves were constructed using the rat tail pressure test for analgesia which indicated a rank order of potency of buprenorphine much greater than morphine greater than butorphanol greater than xorphanol = nalbuphine. Assessment of primary physical dependence liability was made using the technique of chronic intraperitoneal infusion followed by precipitation of abstinence with the opiate antagonist, naloxone. The results clearly indicate that buprenorphine was not only the most potent antinociceptive agent, but also possessed the lowest incidence of physical dependence as indicated by precipitated abstinence signs. The other opiates were very much weaker as antinociceptive agents and all produced clear signs of physical dependence.

Analgesics, Opioid↗
PubMed1985

Substitution and primary dependence studies in animals.

The mixed agonist-antagonist analgesics buprenorphine, butorphanol, nalbuphine, pentazocine and picenadol were compared to the prototype mu and kappa agonists morphine and Mr 2033, respectively, in the following tests in rhesus monkeys: overt behavioral effects upon acute administration in drug-naive animals; discriminative stimulus properties in monkeys trained to respond to either etorphine or ethylketazocine; self-administration of the test agent relative to codeine; single dose suppression and precipitation in withdrawn and non-withdrawn morphine-dependent monkeys, respectively; and primary addiction studies in drug-naive animals. Whereas both buprenorphine and nalbuphine precipitate withdrawal in morphine-dependent monkeys, withdrawal following chronic administration of buprenorphine resulted in no observable signs of abstinence, while nalbuphine withdrawal was similar to that seen in morphine-dependent monkeys. Butorphanol, pentazocine and picenadol all produced mild dependence of the kappa-type; that is, natural withdrawal behavior similar to that seen following chronic Mr 2033 administration.

Animals↗