Vol. 18, pp. 827 to 829 Pergamon Press Ltd 1979. Printed in Great Britain
Neuropharmacolony
PRELIMINARY
NOTE
ENHANCEMENT OF MORPHINE ANALGESIA BY TRICYCLIC ANTIDEPRESSANTS
Roger T. Malseed
and Frederick
J. Goldstein
Pharmacology Section, Department of Biological Philadelphia College of Pharmacy and Science 43rd Street and Kingsessing ?a11 Philadelphia, PA 19104
(Accepted
28 he
Sciences
1979)
Using a cat tail-flick analgetic testing procedure, enhanceSUMMARY: ment of the antinociceptive action of morphine (0.25 mgfkg, s.c.) was detected following pre-treatment (1 hour) with 10 mgfkg, S.C. of either No analgesia was observed following amitriptyline or nortriptyline. S.C. administration of either antidepressant or saline alone. Both centraI (amine re-uptake blockade; anticholinergic) and peripheral (decreased hepatic biotransformation) actions of tricyclic antidepressants may have contributed to augmentation of morphine analgesia. Tricyclic antidepressants, when administered alone, have been shown to produce analgesia in rabbits; moreover, pretreatment with these agents resulted in facilitation of morphine induced antinociception (Saarnivaara and Mattila, 1974). Subsequent investigations in mice and rats demonstrated the potentiating action of chlorimipramine, desipramine and doxepin upon morphine, methadone and propoxyphene analgesia, respectively 1974; Liu and Wang, 1975.; Tofanetti eta., 1977). (Bossa ---I et al Having observed morphine analgesia in the cat utilizing a tail-flick procedure (Goldstein and Malseed, 1979), we decided to examine the interaction of amitriptyline and nortriptyline upon morphine in our system. METHODS Male cats (2.5-4.5 kg) were employed in all experiments. Analgesia was assessed using a cat tail-flick method previously described by the authors (Goldstein and Malseed, A distal segment of the tail was shaved and blackened, and placed in a groove 1979). over a photocell. A high intensity light (source of heat) was focused on the blackened Perception of the stimulus as noxious resulted in a flicking area and a timer activated. of the tail, exposing the photocell, which terminated the stimulus and stopped the timer. The latency of the flick response to the nearest one-tenth of a second was recorded. Cats quickly adapted to handling and positioning of the tail and generally required little restraint. Light intensity was+adjusted to provide a control reaction time of 2.5-6.5 seconds, (average response = 4.4 - 0.3 set ; N = 24). Animals not responding within this time interval were not used for further study. Each cat was tested repeatedly (every 7-10 days); to minimize thermal damage, a cutoff time equal to a 200% increase in the average However, maximum exposure time for pretreatment tail-flick response was employed. any individual reading was limited to 15 seconds where the pretreatment average was Using these parameters, no significant tissue damage was greater than 5 seconds. observed in any of our animals over prolonged testing periods (4-6 months). Four control readings were taken on each animal at 10 minute intervals prior to drug Immediately followadministration and commonly displayed a high degree of consistency. ing the final control reading, either amitriptyline or nortriptyline (10 mg/kg) was injected S.C. and the tail-flick latency was determined at 15, 30 and 60 min. following antidepressant administration. After the 60 min. reading, morphine (0.25 msiks. s.c.) or saline (1.5 ml, s.c.) was administered and the tail-flick latency.again measured at selected intervals for the next 180 minutes. Data are reported as percent change in the latency of the tail-flick response from the pretreatment (i.e., pre-antidepressant) average. Differences between treatments were tested for significance using a multiple range and multiple F test (Duncan, 1955). Doses of all drugs used refer to the respective salts, i.e., morphine sulfate, amitriptyline hydrochloride and nortriptyline hydrochloride.
827
828
Preliminary Note
RESULTS No analgesia was observed during the testing period following S.C. administration of amitriptyline (10 mg/kg), nortriptyline (10 mg/kg) or saline (1.5 ml) alone (Figure 1). Following S.C. injection of 0.25 mg/kg morphine sulfate alone, slight but nonsignificant antinociceptive activity was evident from 30 to 120 min and declined to approximately control levels by 150 min. Pretreatment with either amitriptyline or nortriptyline (at the above dose) significantly (p =. 0.05) enhanced the analgetic response to 0.25 mg/kg morphine sulfate, increasing both the peak and duration of the observable response (Figure 1). Maximal analgesia occurred 180 min after morphine administration in antidepressantpretreated animals, whereas no analgesia was present at this time in animals receiving only morphine, saline or either antidepressant alone.
T IM E
(minutes)
Enhancement of morphine (0.25 mg/kg, s.c.) analgesia by pretreatment with -=+ 10 mg/ g S.C. of either amitriptyline or nortriptyline. Time represents min. after injection of morphine or saline , which was administered one hour following antiValues at each time interval represent percent change in the depressant treatment. tail-flick latency from the pretreatment average and are the mean of four animals. Asterisks indicate analgetic responses that are significantly greater (p = 0.05) N = noitriptyline; A = amitriptyline; M = morphine; than saline control values. S = saline. DISCUSSION Non-analgetic doses of amitriptyline or nortriptyline potentiated antinociceptive activity of morphine in the cat. Similar results involving these and related tricyclic antidepressants have been reported in other species (Bossa eta., 1974; Although tertiary amines were shown to Liu and Wang, 1975; Tofanetti et al_., 1977). be superior narcotic potentiating agents compared to secondary amines in the rabbit 1974; Saarnivaara and Mattila, 1974), our preliminary findings in cats (Bossa et al indicatrn&.;iptyline (secondary) as being approximately equivalent to amitriptyline (tertiary) in this respect. There are several pharmacodynamic actions of tricyclic may explain their narcotic potentiating action:
antidepressants
which
829
Preliminary Note
1.
Blockade
of Biogenic
Amine Re-uptake
Narcotic analgesia has been related to alterations in functional levels of the central monoamines norepinephrine (NE) and serotonin (5-HT), although their respective roles in the overall antinociceptive response remain to be completely Since tricvclics can enhance availaestablished (Mayer and Price, 1976). bility of these biogenic amines by interfering with their prepsynaptic uptake 1978), increased synaptic concentrations of NE and 5-HT (Sulser eta., might augment the effects of morphine in those central pathways subserving antinociception, resulting in enhanced analgesia. 2.
Anticholinergic
Activity
Morphine has been shown to reduce synaptic release of acetylcholine in the cat brain (Beleslin and Polak, 1965). .Tricyclic antidepressants exhibit varying degrees of anticholinergic activity (Peterson et al., 1978), and thus may enhance the ability of morphine to interfere wEh central choljnergic function. 3.
Inhibition
of Biotransformation
Tricyclic antidepressants inhibit the oxidative metabolism of many drugs (Shand and Oates, 1970), including methadone (Liu and Wang, 1975). Therefore, both amitriptyline and nortriptyline may have retarded hepatic biotransformation of morphine, thus prolonging and potentiating its effects. Although both morphine and tricyclic antidepressants can alter central cholinergic, catecholaminergic and serotonergic function, the biochemical basis for the observed We'intend to initate further studies to interaction remains to be established. delineate more precisely the mechanisms of the tricyclic antidepressant-morphine interaction.
REFERENCES Depression by morphine and chloralose Beleslin, D. and Polak, K.L. (1965). 4. Physiol. 117: 411-419. choline release from the cat's brain.
of acetyl-
(1974). Effect of antimitotic Bossa, R., Ferri, S., Galatulas, I. and Santagostino, A. agents on morphine induced analgesia. In: Progress in Chemotherapy (Daikos, G.K., Ed.), Vol. 3, pp 992-994. Athens. Duncan,
D.B.
(1955).
Multiple
range and multipleltests.
Goldstein, F.J. and Malseed, R.T. using a cat tail-flick procedure.
Biometrics
11:
(1979). Evaluation of narcotic analgetic 4. Pharmacol. Methods (In press).
l-59. activity
Increased analgesia and alterations in distribution Liu, S.J. and Wang, R.I.H. (1975). and metabolism of methadone by desipramine in rat. J_. Pharmacol. Exptl. Therap. @5_:
94-104.
Mayer,
Pain 2: --
D3;9 ;;i Price, D.D. (1976). .
Central
nervous
system mechanisms
of analgesia.
Peterson, G.R., Blackwell, B., Hostetler, R.M., Kuzma, R. and Adolphe, A. (1978). cholinergic activity of the tricyclic antidepressants desipramine and doxepin in nondepressed volunteers. Commun. Psychopharmacol. 2: 145-150. Saarnivaara, L. and Mattila, M.J. (1974). antinociception and potentiation rabbits: Psychopharmacol. -35: 221-236. Shand, D.G. and Oates, J.A. (1971). and its inhibition by phenothiazine Pharmacol. 20: 1720-1723. Sulser, drugs.
Anti-
Comparison of tricyclic antidepressants. in of the nonadrenaline pressor responses.
Metabolism of propranolol by rat liver microsomes and tricyclic antidepressant drugs. Biochem.
F., Vetulani, J. and Mobley, P:L. (1978). Biochem. Pharmacol. g-:257-261.
Mode of action
Tofanetti, O., Albiero, L., Galatulas, I. and Genovese, E.(l977). propoxyphene-induced analgesia by doxepin. Psychopharmacol. 51:
’
of antidepressant
Enhancement 213-215.
of
Neuropharmacolony
PRELIMINARY
NOTE
ENHANCEMENT OF MORPHINE ANALGESIA BY TRICYCLIC ANTIDEPRESSANTS
Roger T. Malseed
and Frederick
J. Goldstein
Pharmacology Section, Department of Biological Philadelphia College of Pharmacy and Science 43rd Street and Kingsessing ?a11 Philadelphia, PA 19104
(Accepted
28 he
Sciences
1979)
Using a cat tail-flick analgetic testing procedure, enhanceSUMMARY: ment of the antinociceptive action of morphine (0.25 mgfkg, s.c.) was detected following pre-treatment (1 hour) with 10 mgfkg, S.C. of either No analgesia was observed following amitriptyline or nortriptyline. S.C. administration of either antidepressant or saline alone. Both centraI (amine re-uptake blockade; anticholinergic) and peripheral (decreased hepatic biotransformation) actions of tricyclic antidepressants may have contributed to augmentation of morphine analgesia. Tricyclic antidepressants, when administered alone, have been shown to produce analgesia in rabbits; moreover, pretreatment with these agents resulted in facilitation of morphine induced antinociception (Saarnivaara and Mattila, 1974). Subsequent investigations in mice and rats demonstrated the potentiating action of chlorimipramine, desipramine and doxepin upon morphine, methadone and propoxyphene analgesia, respectively 1974; Liu and Wang, 1975.; Tofanetti eta., 1977). (Bossa ---I et al Having observed morphine analgesia in the cat utilizing a tail-flick procedure (Goldstein and Malseed, 1979), we decided to examine the interaction of amitriptyline and nortriptyline upon morphine in our system. METHODS Male cats (2.5-4.5 kg) were employed in all experiments. Analgesia was assessed using a cat tail-flick method previously described by the authors (Goldstein and Malseed, A distal segment of the tail was shaved and blackened, and placed in a groove 1979). over a photocell. A high intensity light (source of heat) was focused on the blackened Perception of the stimulus as noxious resulted in a flicking area and a timer activated. of the tail, exposing the photocell, which terminated the stimulus and stopped the timer. The latency of the flick response to the nearest one-tenth of a second was recorded. Cats quickly adapted to handling and positioning of the tail and generally required little restraint. Light intensity was+adjusted to provide a control reaction time of 2.5-6.5 seconds, (average response = 4.4 - 0.3 set ; N = 24). Animals not responding within this time interval were not used for further study. Each cat was tested repeatedly (every 7-10 days); to minimize thermal damage, a cutoff time equal to a 200% increase in the average However, maximum exposure time for pretreatment tail-flick response was employed. any individual reading was limited to 15 seconds where the pretreatment average was Using these parameters, no significant tissue damage was greater than 5 seconds. observed in any of our animals over prolonged testing periods (4-6 months). Four control readings were taken on each animal at 10 minute intervals prior to drug Immediately followadministration and commonly displayed a high degree of consistency. ing the final control reading, either amitriptyline or nortriptyline (10 mg/kg) was injected S.C. and the tail-flick latency was determined at 15, 30 and 60 min. following antidepressant administration. After the 60 min. reading, morphine (0.25 msiks. s.c.) or saline (1.5 ml, s.c.) was administered and the tail-flick latency.again measured at selected intervals for the next 180 minutes. Data are reported as percent change in the latency of the tail-flick response from the pretreatment (i.e., pre-antidepressant) average. Differences between treatments were tested for significance using a multiple range and multiple F test (Duncan, 1955). Doses of all drugs used refer to the respective salts, i.e., morphine sulfate, amitriptyline hydrochloride and nortriptyline hydrochloride.
827
828
Preliminary Note
RESULTS No analgesia was observed during the testing period following S.C. administration of amitriptyline (10 mg/kg), nortriptyline (10 mg/kg) or saline (1.5 ml) alone (Figure 1). Following S.C. injection of 0.25 mg/kg morphine sulfate alone, slight but nonsignificant antinociceptive activity was evident from 30 to 120 min and declined to approximately control levels by 150 min. Pretreatment with either amitriptyline or nortriptyline (at the above dose) significantly (p =. 0.05) enhanced the analgetic response to 0.25 mg/kg morphine sulfate, increasing both the peak and duration of the observable response (Figure 1). Maximal analgesia occurred 180 min after morphine administration in antidepressantpretreated animals, whereas no analgesia was present at this time in animals receiving only morphine, saline or either antidepressant alone.
T IM E
(minutes)
Enhancement of morphine (0.25 mg/kg, s.c.) analgesia by pretreatment with -=+ 10 mg/ g S.C. of either amitriptyline or nortriptyline. Time represents min. after injection of morphine or saline , which was administered one hour following antiValues at each time interval represent percent change in the depressant treatment. tail-flick latency from the pretreatment average and are the mean of four animals. Asterisks indicate analgetic responses that are significantly greater (p = 0.05) N = noitriptyline; A = amitriptyline; M = morphine; than saline control values. S = saline. DISCUSSION Non-analgetic doses of amitriptyline or nortriptyline potentiated antinociceptive activity of morphine in the cat. Similar results involving these and related tricyclic antidepressants have been reported in other species (Bossa eta., 1974; Although tertiary amines were shown to Liu and Wang, 1975; Tofanetti et al_., 1977). be superior narcotic potentiating agents compared to secondary amines in the rabbit 1974; Saarnivaara and Mattila, 1974), our preliminary findings in cats (Bossa et al indicatrn&.;iptyline (secondary) as being approximately equivalent to amitriptyline (tertiary) in this respect. There are several pharmacodynamic actions of tricyclic may explain their narcotic potentiating action:
antidepressants
which
829
Preliminary Note
1.
Blockade
of Biogenic
Amine Re-uptake
Narcotic analgesia has been related to alterations in functional levels of the central monoamines norepinephrine (NE) and serotonin (5-HT), although their respective roles in the overall antinociceptive response remain to be completely Since tricvclics can enhance availaestablished (Mayer and Price, 1976). bility of these biogenic amines by interfering with their prepsynaptic uptake 1978), increased synaptic concentrations of NE and 5-HT (Sulser eta., might augment the effects of morphine in those central pathways subserving antinociception, resulting in enhanced analgesia. 2.
Anticholinergic
Activity
Morphine has been shown to reduce synaptic release of acetylcholine in the cat brain (Beleslin and Polak, 1965). .Tricyclic antidepressants exhibit varying degrees of anticholinergic activity (Peterson et al., 1978), and thus may enhance the ability of morphine to interfere wEh central choljnergic function. 3.
Inhibition
of Biotransformation
Tricyclic antidepressants inhibit the oxidative metabolism of many drugs (Shand and Oates, 1970), including methadone (Liu and Wang, 1975). Therefore, both amitriptyline and nortriptyline may have retarded hepatic biotransformation of morphine, thus prolonging and potentiating its effects. Although both morphine and tricyclic antidepressants can alter central cholinergic, catecholaminergic and serotonergic function, the biochemical basis for the observed We'intend to initate further studies to interaction remains to be established. delineate more precisely the mechanisms of the tricyclic antidepressant-morphine interaction.
REFERENCES Depression by morphine and chloralose Beleslin, D. and Polak, K.L. (1965). 4. Physiol. 117: 411-419. choline release from the cat's brain.
of acetyl-
(1974). Effect of antimitotic Bossa, R., Ferri, S., Galatulas, I. and Santagostino, A. agents on morphine induced analgesia. In: Progress in Chemotherapy (Daikos, G.K., Ed.), Vol. 3, pp 992-994. Athens. Duncan,
D.B.
(1955).
Multiple
range and multipleltests.
Goldstein, F.J. and Malseed, R.T. using a cat tail-flick procedure.
Biometrics
11:
(1979). Evaluation of narcotic analgetic 4. Pharmacol. Methods (In press).
l-59. activity
Increased analgesia and alterations in distribution Liu, S.J. and Wang, R.I.H. (1975). and metabolism of methadone by desipramine in rat. J_. Pharmacol. Exptl. Therap. @5_:
94-104.
Mayer,
Pain 2: --
D3;9 ;;i Price, D.D. (1976). .
Central
nervous
system mechanisms
of analgesia.
Peterson, G.R., Blackwell, B., Hostetler, R.M., Kuzma, R. and Adolphe, A. (1978). cholinergic activity of the tricyclic antidepressants desipramine and doxepin in nondepressed volunteers. Commun. Psychopharmacol. 2: 145-150. Saarnivaara, L. and Mattila, M.J. (1974). antinociception and potentiation rabbits: Psychopharmacol. -35: 221-236. Shand, D.G. and Oates, J.A. (1971). and its inhibition by phenothiazine Pharmacol. 20: 1720-1723. Sulser, drugs.
Anti-
Comparison of tricyclic antidepressants. in of the nonadrenaline pressor responses.
Metabolism of propranolol by rat liver microsomes and tricyclic antidepressant drugs. Biochem.
F., Vetulani, J. and Mobley, P:L. (1978). Biochem. Pharmacol. g-:257-261.
Mode of action
Tofanetti, O., Albiero, L., Galatulas, I. and Genovese, E.(l977). propoxyphene-induced analgesia by doxepin. Psychopharmacol. 51:
’
of antidepressant
Enhancement 213-215.
of
