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Further evidence for a bidirectional effect of naloxone on the pain threshold in tolerant and non-tolerant arthritic rats
Neuropeptides
5: 49-52,
FURTHER EVIDENCE FOR THRESHOLD IN TOLERANT V.
Kayser,
J.M.
Besson,
Unite de Recherches 161, 2 rue d’Al&ia,
1984
A BIDIRECTIONAL AND NON-TOLERANT
EFFECT OF NALOXONE ARTHRITIC RATS.
ON THE
PAIN
and G. Guilbaud de Neurophysiologie 75014 Paris (France)
Pharmacologique, (Reprint requests
INSERM U. to V.K.).
ABSTRACT
In arthritic rats, low doses of naloxone induced powerful analgesic effects (as gauged by the vocalization threshold elicited by pressure on the paw) which were marked for 3 and 6 ug/kg IV, whereas high doses (1000 and 3000 ug/kg IV) induced hyperalgesia. This bidirectional effect persisted in arthritic rats rendered tolerant to morphine, but whereas the analgesic effects were suppressed or the hyperalgesic effects induced by the higher doses were reduced, unchanged. These results suggest that the analgesic and hyperalgesic effects might be mediated by different systems. INTRODLCTION
In a model of experimental pain, namely Freund’s adjuvant induced arthritic rats (11, it has been previously shown (2) that there is a dose-dependent bidirectional effect of systemic naloxone: analgesia for higher dose (1000 with low doses (10 - 300 ug/kg IV), hyperalgesia ug/kg
IV>.
In the present study, the effects of various doses of naloxone (1, 3, 6, 10, 600, 1000 and 3000 ug/kg IV) on the vocalization threshold in arthritic rats elicited by pressure of the paw, were studied rendered tolerant to morphine. METHODS
Induction
of morphine tolerance
Tolerance to morphine was induced by subcutaneous (S.C. 1 injections of a sustained release preparation of morphine, according to the technique of Collier et al (31, with minor modifications. A mixture of morphine hydrochloride, suspended in liquid paraffin with an emulsifying agent, mannide monooleate (Arlacel A) was emulsified with 0.9% NaCl and injected S.C. in a volume of 10 ml/kg body weight. A dose of 40 mg/kg of morphine was given on day 1 ; 80 mg/kg on day 2; 120 mg/kg on day 3 ; and 160 mg/kg on day 4. Naloxone was tested on day 5, 24 h after the last injection. Control arthritic animals were 49
injected
with the vehicle
Measurement of the effects
only. of naloxone
The effects of naloxone (administered intravenously into the tail) were evaluated by measuring the vocalization threshold elicited by pressure of the paw in tolerant and non-tolerant arthritic rats, using the Basile analgesymeter (Apelex). For each rat, the control threshold was determined before the injection of naloxone ; thereafter threshold determinations were performed every 5 min after the drug injection, for a period of at least 50 min. RESULTS As previously described, the mean threshold for vocalization was lower in arthritic than in normal rats (see ref. 4). In addition, on day 5, before any acute injection was made, there was no significant difference between th+ vocalization threshold obtained in the vehicletreated (m = 110.52 - 4.33 g) and in the chronically morphine treated rats (m = 108.33 - 3.65 g) (n = 117 rats in each group). Assessment
of morphine tolerance
Tolerance to morphine was estimated by measuring the analgesic effects of an acute injection of morphine (100 to 1000 ug/kg IV). The two lower doses used (100 and 300 ug/kg iv) became totally inefficient in chronically morphine-treated rats compared with that observed in non-tolerant arthritic rats (table I), while the analgesic effect induced by 600 ug/kg was greatly reduced in intensity and A higher dose (1000 ug/kg) elicited a threshold increase duration. comparable to those induced by 100 or 300 ug/kg in non-tolerant arthritic rats, indicating that tolerance had developed (table I). TABLE I Effects of morphine in tolerant and non-tolerant arthritic rats Tolerant Non-tolerant MorDhine dose Maximumvocalization theshold 0) 100 155.6 2 10,5 *+ 104.5 $ 3.4 ns 300 183.3 + 8.8 ++* 108.2 - 4.1 ns 600 223,5 ,+ 7.0 +** 128.6 ,+ 4.3 * 1000 242.6 ,+ 13.9 *** 171 + 4.5 *** Each value dose + P < 0.05 Evaluation
is
expressed *+ P < 0.01
of the effects
in percentage
of
*++
Student’s
P < 0,001.
of naloxone
(table
the
control
n = 9 in
each
t test.
II)
The bidirectional effect of naloxone in non-tolerant arthritic rats was confirmed. Low doses induced significant analgesic effects which were particularly pronounced for 3 and 6 ug/kg. Hyperalgesia was observed with 1000 ug/kg but was not significantly enhanced when
50
increasing the dose up to 3000 ug/kg. In tolerant arthritic rats, the bidirectional effect of naloxone in the curves. Ten was still present ; however, there was a shift ug/kg became totally inefficient, while the analgesic effects of 3 and Hyperalgesia was still obtained with 6 ug/kg were strongly reduced. 1000 and 3000 ug/kg and was comparable to that observed in nontolerant arthritic rats. Interestingly, the dose of 600 ug/kg of naloxone, which induced a slight threshold increase in non-tolerant rats caused hyperalgesia in tolerant animals. These results are summarized in table II and in the figure 1. TABLE II rat Naloxone 1 uo/ka 1 1 3 6 10 600 1000 3000
Effects dose
of
naloxone
in
tolerant
Non-tolerant Maximumvocalization 126.8 207.1 163.0 158.6 115.7 64.7 60.0
2 2.8 + 5.8 _+ 8.6 _+ 6.0 + 5.1 + 5.2 + 3.9
and non-tolerant
arthritic
Tolerant threshold
** +++ *** **+ * +** ***
100.2 142.9 121.7 99.0 76.0 63.17 70.4
2 2.9 _+ 3.6 + 4.08 z 2.4 + 4.6 2.7 $ - 6.51
ns +++ ** ns * +** +*
Each value
dose.
is expressed as a percentage of the control. n = 9 in each * P < 0.05 ** P < 0.01 +** P < 0.001 Student’s t test.
q
1400
g
Non tolerant arthritic rats Tolerant arthritic rats
1300
>
3
9) 1200
c
B
2 1100 c c p"1000 0 % 2 900 5 E" 800
NALOXONE
700
Fig. 1 : Comparison bet+ween tolerant and non tolerant arthritic rats mtheean area (mean - S.E.M.) calculated for each dose of naloxone. Each mean area was calculated from the individual curves obtained for each group of rats, with each value expressed in grams. *+ P < 0.01 *** P < 0.001
51
The injection of naloxone diarrhea and hyperreactivity withdrawal syndrome. These lower doses, appeared 5 min.
induced in each animal teeth chattering, to sensory stimuli, which correspond to a effects, particularly discrete for the after the injection. CONCLUSION
The results reported here indicate that the analgesic effects of low doses of naloxone observed in arthritic rats are strongly reduced in morphine-tolerant animals. They suggest that this paradoxical action of naloxone observed in chronically suffering animals could be related to the involvement of opiate receptors. By contrast, hyperalgesia induced by higher doses was not modified in tolerant animals suggesting that the analgesic and hyperalgesic effects might be related-to different systems.These data-underline the complexity of endogenous opioid systems.
REFERENCES
Use of Freund’s GOURET, C . , MOCQUET, G. and RAYNAUD, G. (1976) adjuvant arthritis test in anti-inflammatory drug screening in the value of animal selection and preparation at the breeding rat: center. Lab. An. Science 26: 281-287. Dose-dependant analgesic and 2. KAYSER, V. and GUILBAUD, G. (1981) hyperalgesic effects of systemic naloxone in arthritic rats. Brain Research 226: 344-348. FRANCIS, D.L. and SCHNEIDER, C. (1972) 3. COLLIER, H.O.J., Modification of morphine withdrawal by drugs interacting with some contradictions and their interpretation. humoral mechanisms: Nature (Land.) 237: 220-223. The analgesic effects of 4. KAYSER, V. and GUILBAUD, G. (1983) morphine, but not those of the enkephalinase inhibitor, Thiorphan, are enhanced in arthritic rats. Brain Research 267: 131-138. 1.
52
5: 49-52,
FURTHER EVIDENCE FOR THRESHOLD IN TOLERANT V.
Kayser,
J.M.
Besson,
Unite de Recherches 161, 2 rue d’Al&ia,
1984
A BIDIRECTIONAL AND NON-TOLERANT
EFFECT OF NALOXONE ARTHRITIC RATS.
ON THE
PAIN
and G. Guilbaud de Neurophysiologie 75014 Paris (France)
Pharmacologique, (Reprint requests
INSERM U. to V.K.).
ABSTRACT
In arthritic rats, low doses of naloxone induced powerful analgesic effects (as gauged by the vocalization threshold elicited by pressure on the paw) which were marked for 3 and 6 ug/kg IV, whereas high doses (1000 and 3000 ug/kg IV) induced hyperalgesia. This bidirectional effect persisted in arthritic rats rendered tolerant to morphine, but whereas the analgesic effects were suppressed or the hyperalgesic effects induced by the higher doses were reduced, unchanged. These results suggest that the analgesic and hyperalgesic effects might be mediated by different systems. INTRODLCTION
In a model of experimental pain, namely Freund’s adjuvant induced arthritic rats (11, it has been previously shown (2) that there is a dose-dependent bidirectional effect of systemic naloxone: analgesia for higher dose (1000 with low doses (10 - 300 ug/kg IV), hyperalgesia ug/kg
IV>.
In the present study, the effects of various doses of naloxone (1, 3, 6, 10, 600, 1000 and 3000 ug/kg IV) on the vocalization threshold in arthritic rats elicited by pressure of the paw, were studied rendered tolerant to morphine. METHODS
Induction
of morphine tolerance
Tolerance to morphine was induced by subcutaneous (S.C. 1 injections of a sustained release preparation of morphine, according to the technique of Collier et al (31, with minor modifications. A mixture of morphine hydrochloride, suspended in liquid paraffin with an emulsifying agent, mannide monooleate (Arlacel A) was emulsified with 0.9% NaCl and injected S.C. in a volume of 10 ml/kg body weight. A dose of 40 mg/kg of morphine was given on day 1 ; 80 mg/kg on day 2; 120 mg/kg on day 3 ; and 160 mg/kg on day 4. Naloxone was tested on day 5, 24 h after the last injection. Control arthritic animals were 49
injected
with the vehicle
Measurement of the effects
only. of naloxone
The effects of naloxone (administered intravenously into the tail) were evaluated by measuring the vocalization threshold elicited by pressure of the paw in tolerant and non-tolerant arthritic rats, using the Basile analgesymeter (Apelex). For each rat, the control threshold was determined before the injection of naloxone ; thereafter threshold determinations were performed every 5 min after the drug injection, for a period of at least 50 min. RESULTS As previously described, the mean threshold for vocalization was lower in arthritic than in normal rats (see ref. 4). In addition, on day 5, before any acute injection was made, there was no significant difference between th+ vocalization threshold obtained in the vehicletreated (m = 110.52 - 4.33 g) and in the chronically morphine treated rats (m = 108.33 - 3.65 g) (n = 117 rats in each group). Assessment
of morphine tolerance
Tolerance to morphine was estimated by measuring the analgesic effects of an acute injection of morphine (100 to 1000 ug/kg IV). The two lower doses used (100 and 300 ug/kg iv) became totally inefficient in chronically morphine-treated rats compared with that observed in non-tolerant arthritic rats (table I), while the analgesic effect induced by 600 ug/kg was greatly reduced in intensity and A higher dose (1000 ug/kg) elicited a threshold increase duration. comparable to those induced by 100 or 300 ug/kg in non-tolerant arthritic rats, indicating that tolerance had developed (table I). TABLE I Effects of morphine in tolerant and non-tolerant arthritic rats Tolerant Non-tolerant MorDhine dose Maximumvocalization theshold 0) 100 155.6 2 10,5 *+ 104.5 $ 3.4 ns 300 183.3 + 8.8 ++* 108.2 - 4.1 ns 600 223,5 ,+ 7.0 +** 128.6 ,+ 4.3 * 1000 242.6 ,+ 13.9 *** 171 + 4.5 *** Each value dose + P < 0.05 Evaluation
is
expressed *+ P < 0.01
of the effects
in percentage
of
*++
Student’s
P < 0,001.
of naloxone
(table
the
control
n = 9 in
each
t test.
II)
The bidirectional effect of naloxone in non-tolerant arthritic rats was confirmed. Low doses induced significant analgesic effects which were particularly pronounced for 3 and 6 ug/kg. Hyperalgesia was observed with 1000 ug/kg but was not significantly enhanced when
50
increasing the dose up to 3000 ug/kg. In tolerant arthritic rats, the bidirectional effect of naloxone in the curves. Ten was still present ; however, there was a shift ug/kg became totally inefficient, while the analgesic effects of 3 and Hyperalgesia was still obtained with 6 ug/kg were strongly reduced. 1000 and 3000 ug/kg and was comparable to that observed in nontolerant arthritic rats. Interestingly, the dose of 600 ug/kg of naloxone, which induced a slight threshold increase in non-tolerant rats caused hyperalgesia in tolerant animals. These results are summarized in table II and in the figure 1. TABLE II rat Naloxone 1 uo/ka 1 1 3 6 10 600 1000 3000
Effects dose
of
naloxone
in
tolerant
Non-tolerant Maximumvocalization 126.8 207.1 163.0 158.6 115.7 64.7 60.0
2 2.8 + 5.8 _+ 8.6 _+ 6.0 + 5.1 + 5.2 + 3.9
and non-tolerant
arthritic
Tolerant threshold
** +++ *** **+ * +** ***
100.2 142.9 121.7 99.0 76.0 63.17 70.4
2 2.9 _+ 3.6 + 4.08 z 2.4 + 4.6 2.7 $ - 6.51
ns +++ ** ns * +** +*
Each value
dose.
is expressed as a percentage of the control. n = 9 in each * P < 0.05 ** P < 0.01 +** P < 0.001 Student’s t test.
q
1400
g
Non tolerant arthritic rats Tolerant arthritic rats
1300
>
3
9) 1200
c
B
2 1100 c c p"1000 0 % 2 900 5 E" 800
NALOXONE
700
Fig. 1 : Comparison bet+ween tolerant and non tolerant arthritic rats mtheean area (mean - S.E.M.) calculated for each dose of naloxone. Each mean area was calculated from the individual curves obtained for each group of rats, with each value expressed in grams. *+ P < 0.01 *** P < 0.001
51
The injection of naloxone diarrhea and hyperreactivity withdrawal syndrome. These lower doses, appeared 5 min.
induced in each animal teeth chattering, to sensory stimuli, which correspond to a effects, particularly discrete for the after the injection. CONCLUSION
The results reported here indicate that the analgesic effects of low doses of naloxone observed in arthritic rats are strongly reduced in morphine-tolerant animals. They suggest that this paradoxical action of naloxone observed in chronically suffering animals could be related to the involvement of opiate receptors. By contrast, hyperalgesia induced by higher doses was not modified in tolerant animals suggesting that the analgesic and hyperalgesic effects might be related-to different systems.These data-underline the complexity of endogenous opioid systems.
REFERENCES
Use of Freund’s GOURET, C . , MOCQUET, G. and RAYNAUD, G. (1976) adjuvant arthritis test in anti-inflammatory drug screening in the value of animal selection and preparation at the breeding rat: center. Lab. An. Science 26: 281-287. Dose-dependant analgesic and 2. KAYSER, V. and GUILBAUD, G. (1981) hyperalgesic effects of systemic naloxone in arthritic rats. Brain Research 226: 344-348. FRANCIS, D.L. and SCHNEIDER, C. (1972) 3. COLLIER, H.O.J., Modification of morphine withdrawal by drugs interacting with some contradictions and their interpretation. humoral mechanisms: Nature (Land.) 237: 220-223. The analgesic effects of 4. KAYSER, V. and GUILBAUD, G. (1983) morphine, but not those of the enkephalinase inhibitor, Thiorphan, are enhanced in arthritic rats. Brain Research 267: 131-138. 1.
52