- Email: [email protected]
Studies on the antinociceptive activities of mixtures of μ- and k-opiate receptor agonists and antagonists
Life Sciences, Vol. 31, pp. 1233-1236 Printed in the U.S.A.
Pergamon Press
STUDIES ON THE ANTINOCICEPTIVE ACTIVITIES OF MIXTURES OF ~- AND k-OPIATE RECEPTOR AGONISTS AND ANTAGONISTS Michael B. Tyers Neuropharmacolo~ Department, Glaxo Group Research Limited, Ware, Hertfordshire U.K. (Received in final form June 14, 1982) Summary Data from interaction studies in the rat with nalorphine/morphine and nalorphine/Mr 2034 mixtures in the tail immersion and paw pressure tests respectively support the concept that antinociception may be mediated via ~- and k-opiate receptors. In addition, apparent pAp values for naloxone suggest that in the paw pressure test alone morphine and Mr 2034 produce antinociception via different mechanisms. The antinociceptive activities of ~- and k-opiate receptor agonists differ qualitatively (1,2,3). Differing relative potencies of agonists in different antinociceptive tests show that while ~-agonists are effective against heat, pressure and chemical-induced pain, drugs which are selective for k-receptors are essentially inactive in heat tests. Thus the possibility exists that an antinociceptive effect against pressure and chemical nociception may be achieved by agonist interaction with either ~- or k-opiate receptors. In the absence of selective antagonists for these receptors, interaction studies have been carried out in the present study with nalorphine, which is a competitive antagonist on ~-receptors and partial agonist on k-receptors, with morphine (~-agonist) and the k-selective benzomorphan Mr 2034. In addition to these studies, apparent pAp values for naloxone against morphine, dextroproproxyphene and Mr 2034 have b~en determined in the paw pressure test in the conscious rat. Materials and Methods Antinociceptive activities of the analgesic drugs were determined in the acetylcholine-induced writhing and hot-plate {55°C) tests in the mouse (male, AHM/i/ICI-derived 18-22g) and in the non-inflamed paw pressure and tail immersion (55°C) tests in the weanling rat (male, AH random bred hooded 35-80g). Details of the methods have been described previously (2). In these studies analgesic drugs were given subcutaneously 20 minutes prior to antinociceptive testing using a blind and randomised dosing protocol. For determination of pA o values for naloxone against morphine, dextroproproxyphene a n d M D 2034 in the paw pressure test naloxone and agonist were given together. For each naloxone/agonist interaction, dose ratios were determined from dose-response curves obtained in three separate tests of the same design. In each test dose groups of 6 rats were used to determine the effects of 3 doses of naloxone on 4-point dose-response curves to the agonist. Values for pA 2 were determined graphically from plots of log (DR-l) x log (antagonist concentration) (4). 0024-3205/82/121233-04503.00/0 Copyright (c) 1982 Pergamon Press Ltd.
1234
Opiate Receptors and Antinociception
Vol. 31, No.s 12 & 13, 1982
For interaction studies with nalorphine, drugs were given together 20 minutes prior to determination of antinociceptive effects. Data are means (±S.E.) of 3 identical tests in which dose-groups of 6 rats were used (i.e. final dose group size: 18 rats). The following drugs were used: morphine HC1, (MacFarlan Smith), D-propoxyphene (Dista), Mr 2034 base (Boehringer-Ingelheim), bremazocine (Sandoz) butorphanol, BL 5572M (Bristol Myers), nalorphine HBr (BW). Results The antinociceptive activities of morphine, Mr 2034, bremazocine, butorphanol, BL 5572M, and nalorphine in the mouse are shown in Table i. Clearly, with the exception of the ~-agonist morphine, these drugs were markedly more potent against acetylcholine induced writhing than in the hot-plate test. These data are consistent with those obtained previously for k-opiate receptor agonists (2). Interaction studies using the tail immersion test showed that nalorphine, iO-9Omg/kg s.c., caused dose-dependent parallel rightward shifts of morphine dose response curves. There was no apparent change in maximum effect although this cannot be stated conclusively because the maximum achievable effects were arbitrary and defined as the cut-off reaction latency of 30s. In the paw pressure test lower doses of nalorphine alone, 0.3-1Omg/kg s.c., caused a low maximum antinociceptive effect and, when combined with Mr 2034, reduced the maximum effect of this full agonist to its own maximum (Fig. 1). Thus, nalorphine behaved as a partial agonist. In the paw pressure test naloxone was more effective in antagonising the antinociceptive effect of the ~-agonists morphine and dextropropoxyphene (pA9 values = 7.48 and 7.56 respectively) than the k-agonist Mr 2034 (pA9 = 6.83)7 In these experiments slopes of the plots log (DR-l) x log (~ntagonist concentration) did not differ significantly from unity. Table 1 Antinociceptive activities of ~- and k-opiate receptor agonists in the mouse Drug
Antinociceptive activities ED50 (±S.E.) mg/kg s.c. Inhibition of ACh writhing
Hot plate (55°C)
Ratio
Morphine
0.45 (0.2-0.9)
1.7 (1.1-2.2)
3.7
Nalorphine
0.12 (0.06-0.3)
>80
>666
Mr 2034
0.06 (0.02-0.16)
>6
>i00
Bremazocine
0.008
>3.2
>400
>25
>333
>90
>7,500
'
(0.003-0.027) Butorphanol
0.075 (0.02-0.2~)
BL 5572M
,
0.012 (0.003-0.038)
Vol. 31, No.s 12 & 13, 1982
Opiate Receptors and Antinociception
1235
200 160
V
Nalorphine /
120
~
o lOj ~"
.o
v~ (n
4)
o. G)
=b
o. q) ¢) (O
0
I
I
I
0.001 0.01 O. 1 1.0 Mr 2034 Dose (mg/kg sc)
200 160
,o.1, \ \
.r O.sc) (mg/kg
IF
120
(0.025q1~1.~ -"
80 40
(0.0) 0
,
0.01
0.1
(0.006) I
I
1
10
I
100
Nalorphine Dose [rng/kg sc) Figure 1 Antinociceptive effects of mixtures of nalorphine and the benzomorphan Mr 2034 in the paw pressure test in the rat. In the upper graph closed circles are Mr 2034 alone; the lower trace is the same data with nalorphine alone shown as open circles.
1236
Opiate Receptors and Antinoclception
Vol. 31, No.s 12 & 13, 1982
Conclusions Antinociceptive data with the k-agonists nalorphine, Mr 2034, ketazocine, bremazocine, butorphanol and BL 5572M in the mouse confirm previous observations that these drugs are essentially inactive in tests employing heat as the nociceptive stimulus. In contrast, agonists selective for ~-opiate receptors, such as morphine, are only slightly less effective in the hot plate test compared with their activities against acetylcholine-induced writhing. In the rat, presssure-induced nociception has similar sensitivity to antinociceptive agents as inhibition of acetylcholine writhing in the mouse (2). Data obtained in interaction studies with nalorphine in the tail immersion and paw pressure tests are consistent with the concept that antinociception produced by morphine and Mr 2034 in th~se tests is mediated through different opiate receptors. Thus, in the tail immersion test nalorphine which had no antinociceptive activity itself, behaved as a competitive antagonist of morphine while in the paw pressure test nalorphine was a partial agonist and reduced the effects of the full agonist Mr 2034 to its own maximum. Thus it is apparent that ~- and k-opiate receptor agonists produce antinociception through two different mechanisms which are clearly distinguishable. However, it is not clear as to whether the antinociceptive effects of these agonists against pressure-induced nociception are also mediated through different receptors. In further studies to investigate this question the differences between the apparent pA 2 values for naloxone against morphine, dextropropoxyphene and Mr 2034 show that naloxone was more effective as an antagonist against the ~-agonists than the k-agonist. Furthermore, the differences in antagonist potency for naloxone were similar to the differences in pap values determined in vitro for naloxone against ~and k-opiate receptor a~onists (5). Accordingly, these latter data suggest that in the paw pressure test an antinociceptive effect may also be produced by interaction with either of two opiate receptors sub-types. References i. W.R. MARTIN, C.G. EADES, J.A. THOMPSON, R.E. HUPPLIER, and P.E. GILBERT, J.Pharmac. exp. Ther. 197:517-532 (1976) 2. M.B. TYERS, Br.J.Pharmac. 69:503-512 (1980) 3. M. SKINGLE, and M.B. TYERS?-Br.J.Pharmac. 70:323-327 (1980) 4. O. ARUNLAKSHANA, and H.O. SCHILD Br.J.Pharmac. 14:48-58 (1959) 5. M. HUTCHINSON, H.W. KOSTERLITZ, F.M. LESLI-~, and A.A. WATERFIELD, Br.J.Pharmac. 55 541-546 (1975)
Pergamon Press
STUDIES ON THE ANTINOCICEPTIVE ACTIVITIES OF MIXTURES OF ~- AND k-OPIATE RECEPTOR AGONISTS AND ANTAGONISTS Michael B. Tyers Neuropharmacolo~ Department, Glaxo Group Research Limited, Ware, Hertfordshire U.K. (Received in final form June 14, 1982) Summary Data from interaction studies in the rat with nalorphine/morphine and nalorphine/Mr 2034 mixtures in the tail immersion and paw pressure tests respectively support the concept that antinociception may be mediated via ~- and k-opiate receptors. In addition, apparent pAp values for naloxone suggest that in the paw pressure test alone morphine and Mr 2034 produce antinociception via different mechanisms. The antinociceptive activities of ~- and k-opiate receptor agonists differ qualitatively (1,2,3). Differing relative potencies of agonists in different antinociceptive tests show that while ~-agonists are effective against heat, pressure and chemical-induced pain, drugs which are selective for k-receptors are essentially inactive in heat tests. Thus the possibility exists that an antinociceptive effect against pressure and chemical nociception may be achieved by agonist interaction with either ~- or k-opiate receptors. In the absence of selective antagonists for these receptors, interaction studies have been carried out in the present study with nalorphine, which is a competitive antagonist on ~-receptors and partial agonist on k-receptors, with morphine (~-agonist) and the k-selective benzomorphan Mr 2034. In addition to these studies, apparent pAp values for naloxone against morphine, dextroproproxyphene and Mr 2034 have b~en determined in the paw pressure test in the conscious rat. Materials and Methods Antinociceptive activities of the analgesic drugs were determined in the acetylcholine-induced writhing and hot-plate {55°C) tests in the mouse (male, AHM/i/ICI-derived 18-22g) and in the non-inflamed paw pressure and tail immersion (55°C) tests in the weanling rat (male, AH random bred hooded 35-80g). Details of the methods have been described previously (2). In these studies analgesic drugs were given subcutaneously 20 minutes prior to antinociceptive testing using a blind and randomised dosing protocol. For determination of pA o values for naloxone against morphine, dextroproproxyphene a n d M D 2034 in the paw pressure test naloxone and agonist were given together. For each naloxone/agonist interaction, dose ratios were determined from dose-response curves obtained in three separate tests of the same design. In each test dose groups of 6 rats were used to determine the effects of 3 doses of naloxone on 4-point dose-response curves to the agonist. Values for pA 2 were determined graphically from plots of log (DR-l) x log (antagonist concentration) (4). 0024-3205/82/121233-04503.00/0 Copyright (c) 1982 Pergamon Press Ltd.
1234
Opiate Receptors and Antinociception
Vol. 31, No.s 12 & 13, 1982
For interaction studies with nalorphine, drugs were given together 20 minutes prior to determination of antinociceptive effects. Data are means (±S.E.) of 3 identical tests in which dose-groups of 6 rats were used (i.e. final dose group size: 18 rats). The following drugs were used: morphine HC1, (MacFarlan Smith), D-propoxyphene (Dista), Mr 2034 base (Boehringer-Ingelheim), bremazocine (Sandoz) butorphanol, BL 5572M (Bristol Myers), nalorphine HBr (BW). Results The antinociceptive activities of morphine, Mr 2034, bremazocine, butorphanol, BL 5572M, and nalorphine in the mouse are shown in Table i. Clearly, with the exception of the ~-agonist morphine, these drugs were markedly more potent against acetylcholine induced writhing than in the hot-plate test. These data are consistent with those obtained previously for k-opiate receptor agonists (2). Interaction studies using the tail immersion test showed that nalorphine, iO-9Omg/kg s.c., caused dose-dependent parallel rightward shifts of morphine dose response curves. There was no apparent change in maximum effect although this cannot be stated conclusively because the maximum achievable effects were arbitrary and defined as the cut-off reaction latency of 30s. In the paw pressure test lower doses of nalorphine alone, 0.3-1Omg/kg s.c., caused a low maximum antinociceptive effect and, when combined with Mr 2034, reduced the maximum effect of this full agonist to its own maximum (Fig. 1). Thus, nalorphine behaved as a partial agonist. In the paw pressure test naloxone was more effective in antagonising the antinociceptive effect of the ~-agonists morphine and dextropropoxyphene (pA9 values = 7.48 and 7.56 respectively) than the k-agonist Mr 2034 (pA9 = 6.83)7 In these experiments slopes of the plots log (DR-l) x log (~ntagonist concentration) did not differ significantly from unity. Table 1 Antinociceptive activities of ~- and k-opiate receptor agonists in the mouse Drug
Antinociceptive activities ED50 (±S.E.) mg/kg s.c. Inhibition of ACh writhing
Hot plate (55°C)
Ratio
Morphine
0.45 (0.2-0.9)
1.7 (1.1-2.2)
3.7
Nalorphine
0.12 (0.06-0.3)
>80
>666
Mr 2034
0.06 (0.02-0.16)
>6
>i00
Bremazocine
0.008
>3.2
>400
>25
>333
>90
>7,500
'
(0.003-0.027) Butorphanol
0.075 (0.02-0.2~)
BL 5572M
,
0.012 (0.003-0.038)
Vol. 31, No.s 12 & 13, 1982
Opiate Receptors and Antinociception
1235
200 160
V
Nalorphine /
120
~
o lOj ~"
.o
v~ (n
4)
o. G)
=b
o. q) ¢) (O
0
I
I
I
0.001 0.01 O. 1 1.0 Mr 2034 Dose (mg/kg sc)
200 160
,o.1, \ \
.r O.sc) (mg/kg
IF
120
(0.025q1~1.~ -"
80 40
(0.0) 0
,
0.01
0.1
(0.006) I
I
1
10
I
100
Nalorphine Dose [rng/kg sc) Figure 1 Antinociceptive effects of mixtures of nalorphine and the benzomorphan Mr 2034 in the paw pressure test in the rat. In the upper graph closed circles are Mr 2034 alone; the lower trace is the same data with nalorphine alone shown as open circles.
1236
Opiate Receptors and Antinoclception
Vol. 31, No.s 12 & 13, 1982
Conclusions Antinociceptive data with the k-agonists nalorphine, Mr 2034, ketazocine, bremazocine, butorphanol and BL 5572M in the mouse confirm previous observations that these drugs are essentially inactive in tests employing heat as the nociceptive stimulus. In contrast, agonists selective for ~-opiate receptors, such as morphine, are only slightly less effective in the hot plate test compared with their activities against acetylcholine-induced writhing. In the rat, presssure-induced nociception has similar sensitivity to antinociceptive agents as inhibition of acetylcholine writhing in the mouse (2). Data obtained in interaction studies with nalorphine in the tail immersion and paw pressure tests are consistent with the concept that antinociception produced by morphine and Mr 2034 in th~se tests is mediated through different opiate receptors. Thus, in the tail immersion test nalorphine which had no antinociceptive activity itself, behaved as a competitive antagonist of morphine while in the paw pressure test nalorphine was a partial agonist and reduced the effects of the full agonist Mr 2034 to its own maximum. Thus it is apparent that ~- and k-opiate receptor agonists produce antinociception through two different mechanisms which are clearly distinguishable. However, it is not clear as to whether the antinociceptive effects of these agonists against pressure-induced nociception are also mediated through different receptors. In further studies to investigate this question the differences between the apparent pA 2 values for naloxone against morphine, dextropropoxyphene and Mr 2034 show that naloxone was more effective as an antagonist against the ~-agonists than the k-agonist. Furthermore, the differences in antagonist potency for naloxone were similar to the differences in pap values determined in vitro for naloxone against ~and k-opiate receptor a~onists (5). Accordingly, these latter data suggest that in the paw pressure test an antinociceptive effect may also be produced by interaction with either of two opiate receptors sub-types. References i. W.R. MARTIN, C.G. EADES, J.A. THOMPSON, R.E. HUPPLIER, and P.E. GILBERT, J.Pharmac. exp. Ther. 197:517-532 (1976) 2. M.B. TYERS, Br.J.Pharmac. 69:503-512 (1980) 3. M. SKINGLE, and M.B. TYERS?-Br.J.Pharmac. 70:323-327 (1980) 4. O. ARUNLAKSHANA, and H.O. SCHILD Br.J.Pharmac. 14:48-58 (1959) 5. M. HUTCHINSON, H.W. KOSTERLITZ, F.M. LESLI-~, and A.A. WATERFIELD, Br.J.Pharmac. 55 541-546 (1975)