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The partial opiate receptor agonists, dezocine and ciramadol act as μ receptor antagonists at the feline ileocecal sphincter
Life Sciences, Vol. 45, pp. 1491-1497 Printed in the U.S.A.
Pergamon Press
THE PARTIAL OPIATE ~ R AGONISTS, DET_OCINE AND CIRAMADOL ACT AS Ix RECEFIOR ANTAGONISTS AT THE FELINE ILEOC~CAL SPHINCTER Ann Ouyang Gastrointestinal Section Hospital of the University of Pennsylvania 3400 Spruce Street Philadelphia, PA 19104-4283 (Received in final form August 9, 1989)
Summary The effects of two novel synthetic narcotic agonist/antagonists dezocine and ciramadol were examined at the ileoeecal sphincter (ICS) in the intact anesthetized cat. Changes in blood pressure were seen with higher doses of both dezocine and ciramadol. No ICS pressure changes were seen in the ICS to dezocine and an increase in ICS pressure was seen only to the highest dose of ciramadol examined (10 mg/kg ). The antagonist aclion oftbe two drugs were examined against submaximal doses of the Ix receptor agonist morphine sulfate, ~ receptor agonist methionine enkephalin and the k-receptor agonist dynorphin. Both drugs inhibit the ICS response to morphine sulfate. No inhibition of the responses to methionine enkephalin or dynorphin were seen with dezocine and only partial inhibition of the ICS response to dynorphin was seen with ciramadol. Opiates have been used since antiquity for their antidiarrheal action. This constipating action can prove an undesirable side effect in patients receiving opiate derivatives for analgesia Two new synthetic partial agonist-antagonist drugs, dezocine (Wy-16,225) and ciramadol (Wy15,705), which appear to be useful for analgesia with minimal gastrointestinal side effects have been developed (1,2,3). The action of these drugs in the intestinal tract has been studied indirectly only using the effect on fecal pellet production in the rat and their antidiarrheal action in mice (1, unpublished data) The specific sites of action in the mammalian intestine is not known. The aims of this study were to examine the effect of both dezocine and ciramadol in the ileocecal sphincter region of the cat, an area where the sites of action of different opiate receptor agonists have been characterized in detail (4,5) and to determine the opioid receptors at which they act.
Methods Details of the method have been described previously (4). Studies were performed in 43 adult domestic male cats weighing between 2.0 and 4.0 kg. Animals were fasted for 24 hours prior to the study. Anesthesia was achieved using i.m. ketamine hydrochloride (10 mg/kg., Ketalar, Parke-Davis, Morris Plains, N.J.) and intravenous chloralose (80mg/ml) in polyethylene
0024-3205/89 $3.00 +.00 Copyright (c) 1989 Pergamon Press plc
1492
Action of Dezocine and Ciramadol at the ICS
Vol. 45, No. 16, 1989
glycol-200. A tracheostomy was performed to allow ventilation using a small animal respirator as necessary. A hepadnized cannula was placed into the femoral artery to allow monitoring of arterial blood pressure. The body temperature was maintained at 370C by means of a heat lamp. All drugs were administered intravenously. The intra-abdominal contents were exposed via a midline incision. The ileocecal sphincter was identified. The contents of the colon were expressed via a small incision made in the distal colon at the pelvic brim. A small incision was made in the ileum about 20 cm orad to the ileocecal sphincter. A triple lumen manometry tube (o.d. 1.2 mm) was inserted via this incision. The manometry tube was constructed of three catheters with side orifices spaced 2 cm apart over the distal segment of the unit. Each lumen was connected to external transducers (Statham P23BB) with a linear calibration of 0-300 mmHg. Each catheter was perfused continuously with distilled water, using a pneumohydraulic low-compliance pump (Arndorfer medical Specialties, Greendale, WI). The manometry catheter was inserted so that the middle orifice was positioned in the ICS as determined by a resting high pressure and a contractile response to phenylephrine ( 251.tg/kg i.v.) The catheter was maintained in place by the insertion of a pin through the ileal wall and through a polyethylene grommet incorporated into the catheter assembly. The output of the strain gauges was recorded on a rectilinear recorder ( Beckman). The segment of bowel was maintained moist using saline, wanned to 37°C and covering the exposed bowel with clear polyethylene wrap. A period of at least 1 hour was allowed for equilibration after manipulation of the bowel. The following drugs were given intravenously: dezocine ( 0.001 mg/kg to 10 mg/kg); ciramadol (0.0001 mg/kg to 10 mg/kg) prepared by Wyeth laboratories; morphine sulfate 1001xg/kg (EliLily, Indianapolis,IN) methionine enkephalin l~tg/kg (Sigma Chemical, St.Louis, MO)and dynorphin 501.tg/kg (Sigma Chemical) and 500pg/kg (-)-N-allylnormetazocine (SKF 10047; a gift from the National Institutes on Drug Abuse, Rockville Md). These doses of morphine sulfate, dynorphin, and methionine enkephalin have been previously shown to be their ED80, ED88 and EDmax respectively in detailed studies examining both the dose response curves of the feline ICS and the sites of action of these drugs at the feline ICS region(4, 5). The baseline intraluminal pressures from the ileocecal sphincter were recorded in millimeters of mercury. The change in maximal pressure recorded during the two minutes preceding the drug and following drug administration were defined as the change in ileocecal sphincter pressure following drug administration. The maximal pressure changes were seen within two minutes with all opioid agonists studied. The change in blood pressure was similarly defined. In antagonist studies, the control response to an opioid was defined in the same way. After at least 45 minutes, the response to the opioid given one minute after the administration of either dezocine or ciramadol was determined as the change in the maximal intraluminal pressure during the two minutes following the opioid compared to the two minutes before the administration of dezocine or ciramadol. The response to the opioid was then expressed as a percent of the control response. After an additional hour, the response to the opioid was again examined to determine whether the control response had returned. The delay of 45 minutes before giving another opioid dose was to ensure that tachyphylaxis would not occur. Statistical analysis was performed using the paired or unpaired Student's t test where appropriate. Data are expressed as mean +SEM.
Results
Effect of dezocine and ciramadol on the ICS pressure and blood vressure The baseline ICS pressure was 19.8+1.9 mmHg(n=20) and baseline arterial blood pressure was 129.1+7.2 mmHg. The dose response curve for the ICS and arterial blood pressure responses to dezocine and ciramadol are shown in figures 1 and 2. No effect at the ICS was seen to dezocine over the dose range of 1 ~tg/kg to 5mg/kg. In contrast, a complex blood pressure
Vol. 45, No. 16, 1989
Action of Dezocine and Ciramadol at the ICS
t
1493
*R
40
20
~
0
E E p
-20 --e- tCS BP
o.
-40 '
c
=
¢(J
-60
-80
-1 O0 -3
, -2
, -1
, 0
1
log dose dezoeine ( mg/kg )
FIGURE 1. Arterial blood pressure and ileocecal sphincter (ICS) pressure changes to dezocine (n>or = 6 for all doses except 10-3mg/kg (n=2). No changes in ICS pressures were seen. A hypertensive response was seen to doses between 5x10 -2 and 5x10 -1 mg/kg. A marked hypotensive response was seen to 5 mg/kg. (*=p<0.05, **=p<0.005, *** = p<0.0005). response was seen, with an increase in arterial pressure seen over a dose range of 50 Ixg/kg to 1 mg/kg and a profound hypotensive response seen with 5 mg/kg ( -76.25mmHg-t:3.3, n=8, p<0.0005). No higher doses were examined because of the blood pressure effect. In response to ciramadol, again no effect on the ICS pressure was seen in response to ciramadol at doses of 0.1Ixg/kg to lmg/kg. A contractile response of 24.9 mmHg +11.3,n=14,p<0.05 was seen in response to 10 mg/kg ciramadol. Again, an effect on the blood pressure was seen at much lower doses with an increase in blood pressure seen at doses abovel0Ixg/kg with a maximal effect seen with 500Ixg/kg of +46.7 mmHg+3.3,n=3,p<0.005. At higher doses of ciramadol, increases in blood pressure were seen although of lesser magnitude ( figure 2). Effect of ¢l¢zocine on th~ ICS responses to ooioid agonists. The effect of 5mg/kg dezocine on the ICS response to morphine sulfate,the Ix receptor agonist, methionine enkephalin, ~ receptor agonist, and dynorphin the k receptor agonist were examined (fig 3) Dezocine at 5 mg/kg abolished the ICS response to morphine sulfate (0-2-0% of control response of 12.0-J:l.5mmHg, n=4).. The response to SKF was examined using a lower
1494
Action
of Dezocine
and Ciramadol
at the ICS
Vol.
45, No,
16,
1989
equivalent dose of the agonist than that used for the other opioids. The ICS response to this lower dose of SKF was inhibited by doses of dezocine above 1001.tg/kg. At 100 gg/kg dezocine the ICS response to 100gg/kg SKF was 32.5+11.7% of the control, n=7 (p<0.005). At doses of dezocine above 500 gg/kg, the response was 11.8-1"13.9% of control (n=3, p<0.025). No inhibition of the ICS response to methionine enkephalin was seen with either lmg/kg dezoeine ( 118.6+_.39.1%of control response of 43.05:15.3 mmHg, n=3) or 5 mg/kg ( 207+66,9% of control response, n=3) Dezoeine (lmg/kg) also failed to antagonize the ICS response to dynorphin (66.7+_33.3% of control response of 27.7_+9.2 mmHg, n=3).
-0-4-
ICS BP
60
t*
"IE
40 ~rlb
E "I
==
20
Q. ¢= .w
tt~
0 ----_I
-20 -4
I
I
. -3
.
. -2
. -1
. 0
1
log d o s e e i r a m a d o l ( m g / k g )
FIGURE 2. Arterial blood pressure and ICS pressure changes to ciramadol (n>or = 5 for all doses except 10-3mg/kg where n=3). A hypertensive response was seen to doses above 10-1mg/kg. No increase in ICS pressure was seen except at a dose of 10 mg/kg (*=p<0.05, **=p<0.005).
Effect of cimmadol on the ICS resoonse to onioid a~onists. The effect of ciramadol on the same opioid agonists was studied (figure 3). Ciramadol abolished the ICS response to 100gg/kg morphine sulfate ( 500 gg/kg ciramadol resulted in a
Vol. 45, No.
16, 1989
Action of Dezocine and Ciramadol at the ICS
1495
response of the ICS of 16.8+7.2% of control, n--4 p<0.005 and lmg/kg ciramadol resulted in an ICS response of 7.7+5.04% of control of 16.6:~.2 mmHg, n=5, p<0.005). In the feline ICS, morphine acts via a cholinergic pathway. In keeping with the effect of SKF being mediated via the same pathway as morphine at this site, presumably at a Ix-receptor (5), ciramadol inhibited the effect of SKF at the ICS (19.95:12.2% of control response of 14.8-t-1.6 mmHg, using 500Ixg/kg ciramadol (n--4, p<0.005) and 5.3.+.2.7 using 1 mg/kg,n=3, p<0.005.In contrast the ICS response to methionine enkephalin after ciramadol (1 mg/kg) was 64.1:1:23.1% of control response of 29.7+7.9 m m H g , n=7, ns. A partial inhibition was seen with dynorphin (57.95: 4.1% of control response of 34.0"1_-9.7 mmHg, n=3, p<0.005).
D
after
dezocine
after
ciramadol
120
100 CL
U
80
60 o
4O
== n
20
morphine sulfate
methionine enkephalin
dynorphin
FIGURE 3. Inhibitory effects of dezocine and ciramadol. The change in the ICS pressure response compared to a control dose of 100 Ixg/kg morphine sulfate, 1 Ixg/kg methionine enkephalin and 50 ktg/kg dynorphin. Dezocine doses were 5 mg/kg vs morphine sulfate and 1 mg/kg vs methionine enkephalin and dynorphin. Ciramadol dose was 1 mg/kg (*p<0.005).
The types of opioid receptors mediating responses at the ileocecal sphincter of the cat have been described previously (4,5). Both morphine and N-allylnormetazocine act via a cholinergic pathway and, from results of tachyphylaxis studies appear to act at the same receptor. This is presumed to be a IXreceptor because the responses to these agonists are inhibited by low doses of naloxone. In contrast, dynorphin and methionine enkephalin act at smooth muscle k- and 3- opioid
1496
Action of Dezocine
and Ciramadol
at the ICS
Vol.
45, No.
16, 1989
receptors as their contractile effects are not inhibited by tetrodotoxin but are inhibited by high doses of naloxone. In this model, neither dezocine or ciramadol cause either a contractile or inhibitory response over a dose range which might be expected to cause analgesia based on studies in rats or monkeys (1) Marked changes in blood pressure were seen at doses lower than were required to cause a contractile response at the ICS. Similar changes in blood pressure have been described in the anesthetized dog, where a minimal hypotensive response was seen to 2 mg/kg intravenous dezocine while a change of -80 mmHg was seen in response to 8 m g / k g . Also similar to the findings in the cat, a mild hypertensive response of 10 mmHg was seen in response to 8 mg/kg ciramadol (6). The absence of changes in motility of the gastrointestinal tract are consistent with studies in which ciramadol had only a minimal effect on the fecal pellet production in rats at high doses and no effect on the prostaglandin E2 induced diarrhea in mice (unpublished data). The antidiarrheal effect of dezocine on PGE2 induced diarrhea in mice was seen only at extremely high doses ( 5 to 10 times doses which afford significant analgesia ) and no constipating effect was seen in rats (1). These initial studies suggested that the ICS would be a useful model in which to investigate the site of antagonist action of these drugs in the mammalian intestine. In the isolated guinea pig ileum, dezocine had no agonist action and an antagonist profile similar to naloxone ( 1 ). The site of the antagonist action of dezocine in the intact cat also appears to be similar to naloxone, being most potent in inhibiting the g receptor agonist morphine.. It abolishes the ICS response to the submaximal dose of morphine sulfate and N-allylnormetazocine. In contrast, no significant inhibition of the response to the 0 or k receptor agonists were seen. A possible enhancing effect on the contractile response to methionine enkephalin may have been missed because of the small number of studies. These findings are consistent with the sites of action of dezocine as previously described (1). A study using the effect of dezocine on the reduction of the anaesthetic requirement of cyclopropane in rats and the effect of the combination of dezocine and morphine suggested that dezocine interacted with IXreceptors (7). Dezocine has also been shown to precipitate withdrawal in the morphine dependent monkey (1). Studies on its ability to serve as a positive reinforcer in nonmorphine dependent monkeys and comparing its profile in discriminative stimulus studies with that of etorphine also suggest a primary action at tx receptors
(8,9). The site of action of ciramadol in the ICS model appears more complex. It abolishes the ICS response to both morphine and N-allylnormetazocine (Ix receptor agonists ) and has no effect on the response to methionine enkephalin (0 receptor agonist). A partial inhibition of the ICS response to dynorphin (k-receptor agonist) is seen suggesting an effect at the k-receptor. Others have shown no binding to k receptors ( unpublished ). It is possible that the inhibitory effect on the action of dynorphin seen in this study may be a dose related phenomenon as naloxone, which is most potent as a Ix receptor antagonist in the ICS (5) will inhibit the effects of dynorphin when given at sufficiently high doses. This study suggests that no effect on gastrointestinal motility is seen in the intact intestine in response to dezocine or ciramadol at doses which would be expected to produce significant analgesia. Both drugs act primarily in the feline intestine as antagonists, primarily to the action of Ix-opioid receptor agonists. Acknowledgements I would like to thank Mr. Peter Vos for his technical assistance and Sidney Cohen, M.D for his advice in this study. The work was supported by NIH grant RO1 Am 34148 and by a grant from Wyeth Laboratories.
Vol. 45, No. 16, 1989
Action of Dezocine and Ciramadol at the ICS
1497
References 1.
2. 3. 4. 5. 6. 7. 8. 9.
J.L. MALIS, M.E. ROSENTHAL, M.I. GLUCKMAN. J. Pharmacol. Exp. Therap. 194 488-498 (1975). A.D. COCHRANE, R. BELL, J.R. SULLIVAN, J. SHAW. Med. J. Aus. 2 501-502 (1979). J.P. YARKDLEY, H. FLETCHER, P.B. RUSSELL. Experientia 34 1124-1125 (1978). A. OUYANG, P. VOS, S. COHEN. Am J Physiol 254 G224-231 (1988). A. OUYANG, C. J. CLAIN, W.J. SNAPE JR., S. COHEN. J.Clin. Invest. 69 507-515, (1982). A.J. LEWIS, T. KIRCHNER. Arch. Int. Pharmacodyn. 250 73-83 (1981). J.C. ROWLINGSON, J.C. MOSCICKI, C.A. DIFAZIO. Anesth Analg. 62 899-902, (1983). G.J. SCHAEFFER, S.G. HOLTZMAN. Pharmacology, Biochemistry and Behaviour. 14 241-245 (1981). A.M. YOUNG, K. R. STEPHENS, D.W.J.H. WOODS. J. Pharmacol and Experimental Therap. 229 118-126 (1984).
Pergamon Press
THE PARTIAL OPIATE ~ R AGONISTS, DET_OCINE AND CIRAMADOL ACT AS Ix RECEFIOR ANTAGONISTS AT THE FELINE ILEOC~CAL SPHINCTER Ann Ouyang Gastrointestinal Section Hospital of the University of Pennsylvania 3400 Spruce Street Philadelphia, PA 19104-4283 (Received in final form August 9, 1989)
Summary The effects of two novel synthetic narcotic agonist/antagonists dezocine and ciramadol were examined at the ileoeecal sphincter (ICS) in the intact anesthetized cat. Changes in blood pressure were seen with higher doses of both dezocine and ciramadol. No ICS pressure changes were seen in the ICS to dezocine and an increase in ICS pressure was seen only to the highest dose of ciramadol examined (10 mg/kg ). The antagonist aclion oftbe two drugs were examined against submaximal doses of the Ix receptor agonist morphine sulfate, ~ receptor agonist methionine enkephalin and the k-receptor agonist dynorphin. Both drugs inhibit the ICS response to morphine sulfate. No inhibition of the responses to methionine enkephalin or dynorphin were seen with dezocine and only partial inhibition of the ICS response to dynorphin was seen with ciramadol. Opiates have been used since antiquity for their antidiarrheal action. This constipating action can prove an undesirable side effect in patients receiving opiate derivatives for analgesia Two new synthetic partial agonist-antagonist drugs, dezocine (Wy-16,225) and ciramadol (Wy15,705), which appear to be useful for analgesia with minimal gastrointestinal side effects have been developed (1,2,3). The action of these drugs in the intestinal tract has been studied indirectly only using the effect on fecal pellet production in the rat and their antidiarrheal action in mice (1, unpublished data) The specific sites of action in the mammalian intestine is not known. The aims of this study were to examine the effect of both dezocine and ciramadol in the ileocecal sphincter region of the cat, an area where the sites of action of different opiate receptor agonists have been characterized in detail (4,5) and to determine the opioid receptors at which they act.
Methods Details of the method have been described previously (4). Studies were performed in 43 adult domestic male cats weighing between 2.0 and 4.0 kg. Animals were fasted for 24 hours prior to the study. Anesthesia was achieved using i.m. ketamine hydrochloride (10 mg/kg., Ketalar, Parke-Davis, Morris Plains, N.J.) and intravenous chloralose (80mg/ml) in polyethylene
0024-3205/89 $3.00 +.00 Copyright (c) 1989 Pergamon Press plc
1492
Action of Dezocine and Ciramadol at the ICS
Vol. 45, No. 16, 1989
glycol-200. A tracheostomy was performed to allow ventilation using a small animal respirator as necessary. A hepadnized cannula was placed into the femoral artery to allow monitoring of arterial blood pressure. The body temperature was maintained at 370C by means of a heat lamp. All drugs were administered intravenously. The intra-abdominal contents were exposed via a midline incision. The ileocecal sphincter was identified. The contents of the colon were expressed via a small incision made in the distal colon at the pelvic brim. A small incision was made in the ileum about 20 cm orad to the ileocecal sphincter. A triple lumen manometry tube (o.d. 1.2 mm) was inserted via this incision. The manometry tube was constructed of three catheters with side orifices spaced 2 cm apart over the distal segment of the unit. Each lumen was connected to external transducers (Statham P23BB) with a linear calibration of 0-300 mmHg. Each catheter was perfused continuously with distilled water, using a pneumohydraulic low-compliance pump (Arndorfer medical Specialties, Greendale, WI). The manometry catheter was inserted so that the middle orifice was positioned in the ICS as determined by a resting high pressure and a contractile response to phenylephrine ( 251.tg/kg i.v.) The catheter was maintained in place by the insertion of a pin through the ileal wall and through a polyethylene grommet incorporated into the catheter assembly. The output of the strain gauges was recorded on a rectilinear recorder ( Beckman). The segment of bowel was maintained moist using saline, wanned to 37°C and covering the exposed bowel with clear polyethylene wrap. A period of at least 1 hour was allowed for equilibration after manipulation of the bowel. The following drugs were given intravenously: dezocine ( 0.001 mg/kg to 10 mg/kg); ciramadol (0.0001 mg/kg to 10 mg/kg) prepared by Wyeth laboratories; morphine sulfate 1001xg/kg (EliLily, Indianapolis,IN) methionine enkephalin l~tg/kg (Sigma Chemical, St.Louis, MO)and dynorphin 501.tg/kg (Sigma Chemical) and 500pg/kg (-)-N-allylnormetazocine (SKF 10047; a gift from the National Institutes on Drug Abuse, Rockville Md). These doses of morphine sulfate, dynorphin, and methionine enkephalin have been previously shown to be their ED80, ED88 and EDmax respectively in detailed studies examining both the dose response curves of the feline ICS and the sites of action of these drugs at the feline ICS region(4, 5). The baseline intraluminal pressures from the ileocecal sphincter were recorded in millimeters of mercury. The change in maximal pressure recorded during the two minutes preceding the drug and following drug administration were defined as the change in ileocecal sphincter pressure following drug administration. The maximal pressure changes were seen within two minutes with all opioid agonists studied. The change in blood pressure was similarly defined. In antagonist studies, the control response to an opioid was defined in the same way. After at least 45 minutes, the response to the opioid given one minute after the administration of either dezocine or ciramadol was determined as the change in the maximal intraluminal pressure during the two minutes following the opioid compared to the two minutes before the administration of dezocine or ciramadol. The response to the opioid was then expressed as a percent of the control response. After an additional hour, the response to the opioid was again examined to determine whether the control response had returned. The delay of 45 minutes before giving another opioid dose was to ensure that tachyphylaxis would not occur. Statistical analysis was performed using the paired or unpaired Student's t test where appropriate. Data are expressed as mean +SEM.
Results
Effect of dezocine and ciramadol on the ICS pressure and blood vressure The baseline ICS pressure was 19.8+1.9 mmHg(n=20) and baseline arterial blood pressure was 129.1+7.2 mmHg. The dose response curve for the ICS and arterial blood pressure responses to dezocine and ciramadol are shown in figures 1 and 2. No effect at the ICS was seen to dezocine over the dose range of 1 ~tg/kg to 5mg/kg. In contrast, a complex blood pressure
Vol. 45, No. 16, 1989
Action of Dezocine and Ciramadol at the ICS
t
1493
*R
40
20
~
0
E E p
-20 --e- tCS BP
o.
-40 '
c
=
¢(J
-60
-80
-1 O0 -3
, -2
, -1
, 0
1
log dose dezoeine ( mg/kg )
FIGURE 1. Arterial blood pressure and ileocecal sphincter (ICS) pressure changes to dezocine (n>or = 6 for all doses except 10-3mg/kg (n=2). No changes in ICS pressures were seen. A hypertensive response was seen to doses between 5x10 -2 and 5x10 -1 mg/kg. A marked hypotensive response was seen to 5 mg/kg. (*=p<0.05, **=p<0.005, *** = p<0.0005). response was seen, with an increase in arterial pressure seen over a dose range of 50 Ixg/kg to 1 mg/kg and a profound hypotensive response seen with 5 mg/kg ( -76.25mmHg-t:3.3, n=8, p<0.0005). No higher doses were examined because of the blood pressure effect. In response to ciramadol, again no effect on the ICS pressure was seen in response to ciramadol at doses of 0.1Ixg/kg to lmg/kg. A contractile response of 24.9 mmHg +11.3,n=14,p<0.05 was seen in response to 10 mg/kg ciramadol. Again, an effect on the blood pressure was seen at much lower doses with an increase in blood pressure seen at doses abovel0Ixg/kg with a maximal effect seen with 500Ixg/kg of +46.7 mmHg+3.3,n=3,p<0.005. At higher doses of ciramadol, increases in blood pressure were seen although of lesser magnitude ( figure 2). Effect of ¢l¢zocine on th~ ICS responses to ooioid agonists. The effect of 5mg/kg dezocine on the ICS response to morphine sulfate,the Ix receptor agonist, methionine enkephalin, ~ receptor agonist, and dynorphin the k receptor agonist were examined (fig 3) Dezocine at 5 mg/kg abolished the ICS response to morphine sulfate (0-2-0% of control response of 12.0-J:l.5mmHg, n=4).. The response to SKF was examined using a lower
1494
Action
of Dezocine
and Ciramadol
at the ICS
Vol.
45, No,
16,
1989
equivalent dose of the agonist than that used for the other opioids. The ICS response to this lower dose of SKF was inhibited by doses of dezocine above 1001.tg/kg. At 100 gg/kg dezocine the ICS response to 100gg/kg SKF was 32.5+11.7% of the control, n=7 (p<0.005). At doses of dezocine above 500 gg/kg, the response was 11.8-1"13.9% of control (n=3, p<0.025). No inhibition of the ICS response to methionine enkephalin was seen with either lmg/kg dezoeine ( 118.6+_.39.1%of control response of 43.05:15.3 mmHg, n=3) or 5 mg/kg ( 207+66,9% of control response, n=3) Dezoeine (lmg/kg) also failed to antagonize the ICS response to dynorphin (66.7+_33.3% of control response of 27.7_+9.2 mmHg, n=3).
-0-4-
ICS BP
60
t*
"IE
40 ~rlb
E "I
==
20
Q. ¢= .w
tt~
0 ----_I
-20 -4
I
I
. -3
.
. -2
. -1
. 0
1
log d o s e e i r a m a d o l ( m g / k g )
FIGURE 2. Arterial blood pressure and ICS pressure changes to ciramadol (n>or = 5 for all doses except 10-3mg/kg where n=3). A hypertensive response was seen to doses above 10-1mg/kg. No increase in ICS pressure was seen except at a dose of 10 mg/kg (*=p<0.05, **=p<0.005).
Effect of cimmadol on the ICS resoonse to onioid a~onists. The effect of ciramadol on the same opioid agonists was studied (figure 3). Ciramadol abolished the ICS response to 100gg/kg morphine sulfate ( 500 gg/kg ciramadol resulted in a
Vol. 45, No.
16, 1989
Action of Dezocine and Ciramadol at the ICS
1495
response of the ICS of 16.8+7.2% of control, n--4 p<0.005 and lmg/kg ciramadol resulted in an ICS response of 7.7+5.04% of control of 16.6:~.2 mmHg, n=5, p<0.005). In the feline ICS, morphine acts via a cholinergic pathway. In keeping with the effect of SKF being mediated via the same pathway as morphine at this site, presumably at a Ix-receptor (5), ciramadol inhibited the effect of SKF at the ICS (19.95:12.2% of control response of 14.8-t-1.6 mmHg, using 500Ixg/kg ciramadol (n--4, p<0.005) and 5.3.+.2.7 using 1 mg/kg,n=3, p<0.005.In contrast the ICS response to methionine enkephalin after ciramadol (1 mg/kg) was 64.1:1:23.1% of control response of 29.7+7.9 m m H g , n=7, ns. A partial inhibition was seen with dynorphin (57.95: 4.1% of control response of 34.0"1_-9.7 mmHg, n=3, p<0.005).
D
after
dezocine
after
ciramadol
120
100 CL
U
80
60 o
4O
== n
20
morphine sulfate
methionine enkephalin
dynorphin
FIGURE 3. Inhibitory effects of dezocine and ciramadol. The change in the ICS pressure response compared to a control dose of 100 Ixg/kg morphine sulfate, 1 Ixg/kg methionine enkephalin and 50 ktg/kg dynorphin. Dezocine doses were 5 mg/kg vs morphine sulfate and 1 mg/kg vs methionine enkephalin and dynorphin. Ciramadol dose was 1 mg/kg (*p<0.005).
The types of opioid receptors mediating responses at the ileocecal sphincter of the cat have been described previously (4,5). Both morphine and N-allylnormetazocine act via a cholinergic pathway and, from results of tachyphylaxis studies appear to act at the same receptor. This is presumed to be a IXreceptor because the responses to these agonists are inhibited by low doses of naloxone. In contrast, dynorphin and methionine enkephalin act at smooth muscle k- and 3- opioid
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receptors as their contractile effects are not inhibited by tetrodotoxin but are inhibited by high doses of naloxone. In this model, neither dezocine or ciramadol cause either a contractile or inhibitory response over a dose range which might be expected to cause analgesia based on studies in rats or monkeys (1) Marked changes in blood pressure were seen at doses lower than were required to cause a contractile response at the ICS. Similar changes in blood pressure have been described in the anesthetized dog, where a minimal hypotensive response was seen to 2 mg/kg intravenous dezocine while a change of -80 mmHg was seen in response to 8 m g / k g . Also similar to the findings in the cat, a mild hypertensive response of 10 mmHg was seen in response to 8 mg/kg ciramadol (6). The absence of changes in motility of the gastrointestinal tract are consistent with studies in which ciramadol had only a minimal effect on the fecal pellet production in rats at high doses and no effect on the prostaglandin E2 induced diarrhea in mice (unpublished data). The antidiarrheal effect of dezocine on PGE2 induced diarrhea in mice was seen only at extremely high doses ( 5 to 10 times doses which afford significant analgesia ) and no constipating effect was seen in rats (1). These initial studies suggested that the ICS would be a useful model in which to investigate the site of antagonist action of these drugs in the mammalian intestine. In the isolated guinea pig ileum, dezocine had no agonist action and an antagonist profile similar to naloxone ( 1 ). The site of the antagonist action of dezocine in the intact cat also appears to be similar to naloxone, being most potent in inhibiting the g receptor agonist morphine.. It abolishes the ICS response to the submaximal dose of morphine sulfate and N-allylnormetazocine. In contrast, no significant inhibition of the response to the 0 or k receptor agonists were seen. A possible enhancing effect on the contractile response to methionine enkephalin may have been missed because of the small number of studies. These findings are consistent with the sites of action of dezocine as previously described (1). A study using the effect of dezocine on the reduction of the anaesthetic requirement of cyclopropane in rats and the effect of the combination of dezocine and morphine suggested that dezocine interacted with IXreceptors (7). Dezocine has also been shown to precipitate withdrawal in the morphine dependent monkey (1). Studies on its ability to serve as a positive reinforcer in nonmorphine dependent monkeys and comparing its profile in discriminative stimulus studies with that of etorphine also suggest a primary action at tx receptors
(8,9). The site of action of ciramadol in the ICS model appears more complex. It abolishes the ICS response to both morphine and N-allylnormetazocine (Ix receptor agonists ) and has no effect on the response to methionine enkephalin (0 receptor agonist). A partial inhibition of the ICS response to dynorphin (k-receptor agonist) is seen suggesting an effect at the k-receptor. Others have shown no binding to k receptors ( unpublished ). It is possible that the inhibitory effect on the action of dynorphin seen in this study may be a dose related phenomenon as naloxone, which is most potent as a Ix receptor antagonist in the ICS (5) will inhibit the effects of dynorphin when given at sufficiently high doses. This study suggests that no effect on gastrointestinal motility is seen in the intact intestine in response to dezocine or ciramadol at doses which would be expected to produce significant analgesia. Both drugs act primarily in the feline intestine as antagonists, primarily to the action of Ix-opioid receptor agonists. Acknowledgements I would like to thank Mr. Peter Vos for his technical assistance and Sidney Cohen, M.D for his advice in this study. The work was supported by NIH grant RO1 Am 34148 and by a grant from Wyeth Laboratories.
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References 1.
2. 3. 4. 5. 6. 7. 8. 9.
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