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Effects of cocaine, cocaine metabolites and cocaine pyrolysis products on the hindbrain cardiac and respiratory centers of the rabbit ag
Life Sciences. Vol. 57, No. 20, pp. 1861-1868,199S 1995 FZlsevierScience Inc. Printed in the USA. AU rights reserved 0024-3205195 $950 + .oo
Pergamon 0024-3205(95)02166-3
EFFECTS OF COCAINE, COCAINE METABOLITES AND COCAINE PYROLYSIS PRODUCTS ON THE HINDBRAIN CARDIAC AND RESPIRATORY CENTERS OF THE RABBIT H. K. Erzouki, A. C. Allen, A. H. Newman, S. R. Goldberg and C. W. Schindler Preclinical
Pharmacology Laboratory, NIH/NIDA Division of Intramural Research, Addiction Research Center, P.O. Box 5 180, Baltimore, MD 2 1224 (Received in final form September 8, 1995)
Summarv Hemodynamic and respiratory effects of vertebral artery or i.v. administration of cocaine, cocaine metabolites and cocaine pyrolysis products were measured in anesthetized rabbits. Vertebral artery administration of 1 mg of cocaine produced decreases in blood pressure and heart rate and respiratory arrest. Cocaethylene (1 mg), a cocaine metabolite produced following co-administration of cocaine and ethanol, had comparable effects except that the respiratory arrest following cocaethylene had a longer duration of action than did cocaine. A decrease in blood pressure was also observed following 1 mg of norcocaine; however, unlike cocaine, norcocaine did not affect respiration. Acute tolerance was not observed to any of the effects of 1 mg of cocaine, cocaethylene or norcocaine following vertebral artery administration. None of these compounds had significant effects following i.v. administration of the same dose. The cocaine metabolites benzoylecgonine and ecgonine methyl ester were without effect by either route in doses up to 3 mg. In contrast to cocaine, the cocaine pyrolysis products anhydroecgonine methyl ester (3 mg) and noranhydroecgonine methyl ester (3 mg) produced similar effects via both routes of administration. Both compounds produced decreases in blood pressure and heart rate and an increase in respiratory rate. Anhydroecgonine ethyl ester (3 mg), a metabolite hypothetically formed from the cocaine pyrolysis product in individuals co-administering ethanol, had effects similar to the other pyrolysis products, although its effects were not as prominent via the i.v. route of administration. Acute tolerance was observed upon administration of the cocaine pyrolysis products. These results indicate that the cocaine pyrolysis products do not share a common mechanism of action with either cocaine or the cocaine metabolites. Key Words: cocaine, cocaine metabolites, cocaine pyrolysis products, hindbrain, cardiac center, respiratory center ‘l‘he cardiac and respiratory
complications following cocaine administration often arise hours after cocaine administration (1,2) when cocaine blood levels would be low or undetectable. This suggests a role for cocaine metabolites in these effects as many of the metabolites have Because of their long half-lives, a half-lives that are much longer than that of cocaine. progressive increase in the level of these metabolites would also be expected following repeated dose “bingeing” as often occurs with cocaine abuse. In addition, cocaine is frequently used in the form of smoked “crack” cocaine. When cocaine is smoked a variety of cocaine pyrolysis products are produced. These compounds might also be expected to contribute to cocaine’s Corresponding Author: Hashim K. Erzouki, Preclinical NIH/NIDA/DIR, PO Box 5180, Baltimore, MD 21224
Pharmacology
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overall effects. Further, while early reports seemed to indicate that the metabolites had few effects, there have been recent reports of significant effects of many of the metabolites, including effects on the cardiovascular system (3). Under normal circumstances, cocaine is metabolized to benzoylecgonine and ecgonine methyl ester (EME), with lesser amounts of norcocaine and a variety of other metabolites appearing following all routes of administration. For example, following i.v. administration, the urinary excretion levels of both benzoylecgonine and EME quickly exceed those of cocaine and account for up to 90% of recovered cocaine products from urine (4). Similar results are found following “crack” cocaine smoking. Levels of norcocaine following crack smoking are approximately methyl ester (AEME) results from the one-tenth those of cocaine itself (5). Anhydroecgonine elimination of benzoic acid from cocaine under the high temperature conditions of pyrolysis. AEME has been documented to be the major volatile pyrolysis product formed under free-base cocaine smoking conditions (6). AEME has also been detected in research subjects who smoked cocaine (5) with most subjects excreting substantial amounts of AEME averaging approximately half the molar amounts of cocaine excreted during a 48hr collection period (7,8). The other potential cocaine pyrolysis products evaluated for this report (anhydroecgonine ethyl ester, AEEE; and noranhydroecgonine methyl ester, NAEME) have not been as extensively characterized, however, their formation is likely due to metabolic and pyrolysis processes that are know to occur with cocaine (9). When cocaine administration and alcohol consumption overlap, the novel metabolite cocaethylene is produced in viva. Cocaethylene also has been found as an impurity of both pharmaceutical and illicit cocaine manufacture (10). In human postmortem blood, concentrations of cocaethylene have been reported to nearly equal those of cocaine itself (11). The purpose of the current study was to characterize the effects of cocaine and its metabolites and pyrolysis products on cardiac and respiratory activity. While the hemodynamic effects of cocaine have been extensively documented, its effects on the respiratory system have been studied less extensively. Available data suggest that cocaine’s primary site of action on respiratory function is in the hindbrain, most probably the ventrolateral medulla (12). Since both cardiovascular and respiratory effects of cocaine are thought to play a large role in cocaine toxicity (13), the focus of the current study was on the cardiovascular and respiratory effects of cocaine administered to the hindbrain of the rabbit by way of vertebral artery administration. The use of this procedure required experiments to be performed in anesthetized animals. While anesthesia can blunt the sympathomimetic effects of cocaine on cardiovascular function (14), previous research has shown that the use of anesthesia does not affect the hindbrain response to cocaine (12). Thus, the use of anesthesia allows the determination of the isolated hindbrain response to cocaine with minimal influences of other brain areas. Methods Studies were conducted in anesthetized adult rabbits, of both sexes, which ranged in weight from 2.5 to 3.5 kg. They were anesthetized with sodium pentobarbital (30-35 mgkg, iv.). A longitudinal incision was made in the neck region overlying the trachea and the trachea was exposed, cannulated and connected to a respiratory monitor (MicroSpan 9090-A, Biochem). Respiratory activity was monitored for Animals were allowed to breathe spontaneously. respiratory rate and partial pressure of CO2 (expired, end-tidal C02). If breathing stopped following drug administration, the animals were immediately placed on artificial ventilation. Artificial ventilation was carried out using a respiratory frequency of 40-60 and a tidal volume of 15 cc. These parameters were adjusted to maintain a constant blood pH. Thereafter, the respirator was turned off every 5- 10 min to determine whether respiration had recovered. Body temperature was maintained between 37.0 and 38.OoC (rectal) by an electric heating pad. The femoral artery was cannulated with polyethylene tubing (PE 160) which was filled with heparinized saline (10 USP units/ml). This arterial catheter was connected to a blood pressure transducer (T42-20, Coulboum Instruments, Lehigh Valley, PA). The transducer was connected to an associated amplifier (S72-25, Coulbourn) and blood pressure processor (S77-34, Coulbourn). The blood pressure processor analyzed the raw transducer signal, giving analog
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outputs of systolic (SP), diastolic (DP) and mean pressure (DP + [(SP - DP)/31) after each cardiac cycle. The signal for the end of the cardiac cycle was fed into an Apple IIe computer. For each cycle the computer measured time between cycles with a resolution of 1 msec and read the analog signals for pressure with a resolution of 1 mm Hg. These values were summed and averaged over periods of 30 set for subsequent analysis. The transducer was routinely calibrated manually with a manometer and adjusted to maintain the 1 mm Hg accuracy and linearity over a range of approximately 50 to 250 mm Hg. Lead II of a surface EKG (speed 100 mm/set) was routinely monitored and heart rate was calculated from the EKG tracing. To administer drug to the hindbrain areas, the standard technique of vertebral artery administration was used. For vertebral artery drug administration, a retrograde cannulation of the axillary artery was performed. The tip of the cannula was positioned at the bifurcation of this vessel with one vertebral artery after ligating the cervical, thyrocervical and internal mammary arteries (15). When drug injections were carried out, the vertebral artery was briefly clamped between the bifurcation and the heart. The clamp was removed after injection of a bolus dose of the drug, thus allowing the flow of blood to deliver drug to the hindbrain. For comparison the femoral vein was cannulated and identical doses were also administered intravenously. As less than one-fourth of a intravenously administered dose of cocaine would be expected to reach the brain, and a considerably smaller amount would be expected to reach the hindbrain, any difference in effect observed between i.v. and vertebral artery administration can be attributed to a difference in the amount of the drug reaching the hindbrain. A dose of 1 mg was tested initially for all drugs as preliminary research had shown that for cocaine this dose would produce clear effects in the hindbrain with little or no effect following systemic administration, If no clear effect was observed following 1 mg via the vertebral artery route, the dose was increased up to 3 mg. A fixed dose was used because the total brain weight for rabbits varying in weight from 2.5-3.5 kg varies less than 20% and is not clearly correlated with body weight (16). Drugs. The drugs used were cocaine hydrochloride (NIDA, MW 340), cocaethylene hydrochloride (RBI, Natick MA, MW 354), benzoylecgonine (Sigma Chemical, St. Louis, MW 289) norcocaine hydrochloride (RBI, MW 326), ecgonine methyl ester mesylate (Sigma, MW 236) and sodium pentobarbital (Sigma). Anhydroecgonine methyl ester (AEME, MW ISI), noranhydroecgonine methyl ester (NAEME, MW 167), and anhydroecgonine ethyl ester (AEEE, MW 18 1) were prepared by A. A. as described elsewhere (9). All drugs were dissolved in saline and injected in a volume of 0.25 ml. Doses are as the salt where appropriate. Data Analysis. Baseline values for all measures were taken 10, 5 and 2.5 min prior to drug administration. All drug effects reported are the peak effect observed which typically occurred within 2-7 min after drug administration. Data for each compound were analyzed with a twoway repeated measures analysis of variance (ANOVA), with one repeated measures factor (baseline versus peak effect) and one grouping factor (route of administration). Data on repeated dose effects were analyzed with a one-way (injection number) repeated measures ANOVA. Follow-up contrasts were used to determine individual effects (17). Results Cocaine (1 mg) administered into the vertebral artery resulted in decreases in both arterial blood pressure and heart rate, and also produced respiratory arrest (Table 1). The decreases in pressure and heart rate occurred within 1 min of the injection and peaked within 2 to 5 min. The time course for respiratory arrest was similar. Blood pressure, heart rate and respiration remained depressed to well below pre-drug values for lo-15 min, with recovery to baseline occurring 30-45 min following cocaine administration. In contrast to vertebral artery administration, i.v. administration of 1 mg cocaine had no significant effect on any of the parameters measured. With cocaethylene (Table 1), the profile of hemodynamic effects was similar to that of cocaine, although the effects were smaller. Blood pressure was clearly reduced following vertebral artery administration and there was a tendency for heart rate to be decreased. Respiratory arrest As with cocaine, i.v. administration of also occurred following cocaethylene administration.
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TABLE 1 EFFECTS OF COCAINE AND ITS METABOLITES ON HEMODYNAMIC AND RESPIRATORY ACTIVITY (N=6) DRUG/ ROUTE
MBP
COC VA
BASELINE VALUES HR RR
CO2
MBP
33+1
-25+4**
67+8
183+18
24&3
cot IV _ _ _ _78~7 _cE_vA_ 56&-
183@
23&3
-l?&lO-
39g - - ;6+2- - -3?+2-
CE IV -Nc-v?A-
79$ - - - -80+8-
200+10 -2ijlfi2-
2,+ - ‘21_
NC IV -BE-Vi-
36+2 204$3 25&2 79+ - - - 74+10- -l&l l- - - :6+3- - -3-&2-
1889 BE IV _E;ME_vA_ _ _ _ 84&8 _ 83+4- -28&O92+5
EME IV
39$3 - -4i+2-
4011 2l$l - - 34+3- - -2;+2-
313+13
37*3
31+3
PEAK CHANGES HR RR -28+6**
CO2
-24+3**
5+2 123 523 ----=-----_-. - --19~2~*: --i2&3 -2&_2** 4&4 - X5&4;*
- - -l+l1+4
-l+l 2+1
26&2_5 5*1* O&l - &3- - - 2+1- - --i+l-
2$4 225 3*1 - - -2+3- - - -4_+4 - - -2ki -l&2
13+3**
O+_l - - &l-
11+0
021 O&l - - -3+2- - - 12+1- - - 2+2-15+12
l+l
o+o
Note: Doses are 1 mg. Values are mean + SEM. Peak changes are from baseline. *p<.O5, **p<.Ol from baseline for individual drug and route. MBP=mean blood pressure (mm Hg), HR=heart rate (beats/min), RR=respiratory rate, COC=cocaine, CE=cocaethylene, NC=norcocaine, BE=benzoylecgonine, EME= ecgonine methyl ester, VA=vertebral artery, IV=intravenous.
TABLE 2 EFFECTS OF COCAINE AND THE PYROLYSIS PRODUCTS ON HEMODYNAMIC AND RESPIRATORY ACTIVITY (N=6) BASELINE VALUES RR HR
DRUG/ ROUTE
DOSE
MBP
COC VA
1
67&8
183+18
24+3
CO2
MEW
33+1
-25+4**
PEAK CHANGES RR HR -2&6**
-24k3 **
CO2 13+3**
5+2 -121 183H_ 2$3 1 78kz 39+4 l&3_ 5+3_ - 3- - 91+4 - 206+16 - -24+3 - -3”” - --i2+5 ;+--i&3 - - ii+2 - - 4+2- 8+35+ -7+ - - I+ -15;3 84+5 222&7_ 24-q AEMElV 3 32*1 AEEkiA- ‘j- - &$ - -2:0+8 - 22+2 - >7+2 - - -7fL - --i&3- ;; iI--*’ --8+3- -13”3_ 5+2 -2&2 189&_ AEEEIV 3 32’ 2+7_ 68$ 2;_’ 3- - -85+6 - 214+20 - -22+4 - -32+2 - --i7+6 - - -2&-5 - - -9;; - - -2+2- _24+5l++ 7+1 32+3 78+4 203+5 20+5 NAEMEIV 3 -5Zk3 - I++ _9+2 **
cot IV AEM;+A-
-$&&-A-
-‘0”1
I++ 1
I+
I++
Note: Doses are in mg. Values are mean + SEM. Peak changes are from baseline. *p<.O5, **p<.Ol from baseline for individual drug and route. +p<.O5, ++p<.Ol from baseline for individual drugs where the route factor was not significant. See Table 1 for abbreviations except AEME=anhydroecgonine methyl ester, AEEE= anhydroecgonine ethyl ester, NAEME=noranhydroecgonine methyl ester.
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cocaethylene had little effect except for a small rise in respiratory rate. In contrast to both cocaethylene and cocaine, vertebral artery administration of 1 mg norcocaine (Table 1) had no effect on respiration, although a clear decrease in blood pressure was noted. Again, i.v. The time course for the effects for administration of norcocaine was without effect. cocaethylene and norcocaine were similar to cocaine, except that the respiratory depressant effect of cocaethylene lasted up to 40-60 min following administration and did not recover during the duration of the experiment in 2 of the 6 rabbits. Neither 1 mg benzoylecgonine nor ecgonine methyl ester (Table 1) had any effects by either the vertebral or i.v. routes. As a result, we also administered both compounds at a higher dose (3 mg), but again no significant effects were observed (vertebral artery change scores for 3 mg BE, MBP -1 + 1, HR 1 & 5, RR 2 +2,C02lrf:1;3mgEME,MBP4+l,I-IR1+1,RR5+5,C02 +l>. To test for acute tolerance, after the first injection of cocaine or norcocaine and once all measures had returned to baseline (usually in about 45 min), an additional 1 mg dose of the drug was administered via the vertebral artery; after an additional period of time was allowed for measures to again return to normal (again, about 45 min), a third 1 mg dose was administered. Figure 1 shows the respiratory depressant effect of cocaine following its initial administration and following the two subsequent administrations. Clearly, the respiratory depressant effects were as prominent after the second and third administrations as after the first. For the other effects of both cocaine and norcocaine, these subsequent administrations produced effects that were always comparable to the initial vertebral artery administration. With cocaethylene it was not always possible to administer additional doses, since in some animal’s respiration never recovered to baseline. In those animals in which baseline values recovered to baseline, subsequent vertebral artery administrations of cocaethylene had comparable effects to its initial administration.
-10 -
COCAINE
1
2
3
CONSECUTIVE COCAINE ADMINISTRATIONS
Fig. 1 Effects of cocaine and AEME on respiratory rate following vertebral artery administration. Subsequent administration of drugs (injections 2 and 3) were each given once respiratory rates returned to baseline following the previous administration (usually in about 45 min). Values are mean changes from baseline + S.E.M. *p < .05 from baseline. +p < .05 from injection #l.
l&i6
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In table 2 the results with the cocaine pyrolysis products (AEME, NAEME, AEEE) are presented. For comparison, the results with cocaine are also presented. Preliminary work with doses of 1 or 2 mg of these compounds indicated they produced no significant effects via the vertebral artery route. However, vertebral artery administration of a 3 mg dose of all three of these compounds (AEME, NAEME, AEEE) produced decreases in blood pressure and heart rate similar to those seen with cocaine (Table 2); the onset of these effects were within 2-4 min, with the peak effect occurring 5-7 min after administration and a duration of 20-30 min. In contrast to cocaine, all three compounds increased respiratory rate. The onset of this effect was immediate. Also in contrast to cocaine, i.v. administration of AEME and NAEME produced This was also true for AEEE on heart effects comparable to vertebral artery administration. rate, but not on blood pressure or respiration. The time course for the effects following i.v. administration of AEME, NAEME or AEEE was similar to that following vertebral artery administration. For blood pressure, heart rate and respiratory rate, route of administration was not a significant factor (i.e., only the main effect for drug was significant following the ANOVA analysis). As with cocaine, once the measures had returned to baseline (usually in about 45 min), additional doses of the drugs were administered. In contrast to cocaine, subsequent administrations of the pyrolysis products failed to produce clear changes in any of the parameters measured. Figure 1 shows the results with AEME on respiratory rate following vertebral artery administration. Initially, AEME increased respiratory rate by approximately 12 breaths/mitt, however, increases in respiratory rate were much smaller following the second and third administrations.
Discussion The hemodynamic effects of cocaine following vertebral artery administration in the present study are consistent with other studies of central administration of cocaine in anesthetized animals. Raczkowski et al. (12) reported a similar decrease in blood pressure and heart rate following vertebral artery administration of cocaine in the cat, and Barber and Tackett (18) reported similar effects in the rat following i.c.v. administration of cocaine. Raczkowski et al. (12) also reported respiratory depressant effects of cocaine following vertebral artery administration, although they observed effects on tidal volume and not respiration rate. The fact that i.v. administration of the same dose of cocaine failed to have significant effects, suggests that the effects of cocaine administered through the vertebral artery were mediated primarily in the hindbrain of the rabbit, and not at a more remote central or peripheral site. The profile of hemodynamic effects of cocaethylene in the present study was similar to that of cocaine. This similarity in effect is consistent with previous work using systemic administration of this compound (19,20). However, the respiratory depressant effect of cocaethylene was of longer duration than that of cocaine, which may account for the finding that cocaethylene is slightly more potent than cocaine in terms of lethality (21,22). Unlike cocaine and cocaethylene, norcocaine did not produce respiratory depression. The reason for the discrepancy between the two compounds in producing respiratory depression is unclear. Norcocaine has comparable potency to cocaine for binding to both the DA and NE transporters, although norcocaine is approximately 5 times more potent than cocaine for binding to the 5HT transporter (23). In addition, both cocaine and norcocaine are potent local anesthetics (24). Like cocaine, norcocaine had differential effects via the vertebral versus the i.v. route, again suggesting that its effects following vertebral artery administration are mediated in the hindbrain. Neither benzoylecgonine nor ecgonine methyl ester produced any significant effects when administered through the vertebral artery, which may reflect the fact that neither of these compounds are potent local anesthetics (24). Acute tolerance was not observed over three successive vertebral artery administrations with cocaine, cocaethylene or norcocaine. This is in contrast to previous results with i.v. administrated cocaine in rats (25) and cats (26). While this discrepancy may be due to the species of animal used, it more likely results from the route of administration. Nevertheless, it is possible that the failure to observe acute tolerance to the hindbrain effects of these compounds may well hinder the development of acute tolerance even following i.v. administration.
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The spectrum of effects for the pyrolysis products of cocaine were clearly different from that of cocaine itself. The pyrolysis products produced small increases in respiratory rate rather than the clear decrease observed with cocaine. This small increase in respiratory rate might be expected to counteract the respiratory depressant effect of cocaine. However, as acute tolerance was observed for the respiratory stimulant effect of the pyrolysis products, but not for the respiratory depressant effect of cocaine, this counteracting effect would be short-lived. In addition, the pyrolysis products generally produced comparable changes following both i.v. and vertebral artery administration, suggesting that their effects were not mediated in the hindbrain, but at a more remote central site or in the periphery. Thus, even when the pyrolysis products were producing comparable effects to cocaine, such as on blood pressure and heart rate, it is likely that these effects were mediated at different sites and perhaps through different receptor mechanisms. While little evidence is available on the mechanisms of action for the cocaine pyrolysis products, what evidence is available is consistent with the present findings suggesting that the effects of the pyrolysis products are mediated through different mechanisms than for cocaine. Newman et al. (9) reported that none of the pyrolysis products bind to cocaine recognition sites on the dopamine transporter in rat caudate-putamen, nor do they produce behavioral or toxicological effects comparable to cocaine. In addition, these drugs also do not bind with appreciable affinity to either brain muscarinic or nicotinic receptors. El-Fawal and Wood (27) did observe an anticholinergic effect of AEME when tested in vitro. This group (28) also observed bronchoconstriction and decreases in body temperature when AEME was given into the lung, but not when it was given i.v., suggesting that the effect may have been due to local lung irritation. Therefore, it is unclear how these drugs produced their effects in the present study. The observation that the effects of the pyrolysis products do not appear to be mediated in the hindbrain, suggests mediation in the periphery where different receptor systems may be involved. In summary, the present results indicate that both cocaine and cocaethylene act in the hindbrain of the rabbit to decrease blood pressure, heart rate and respiration rate. Cocaethylene had a longer duration of action than cocaine in depressing respiration. In addition, there was no acute tolerance to the hindbrain effects of these drugs. Norcocaine also acted in the hindbrain to decrease blood pressure. Following systemic administration at doses high enough to reach hindbrain concentrations similar to those observed here, these hindbrain effects of both cocaine and its metabolites would certainly be expected to contribute to the overall effect of cocaine. Of course, at these higher doses peripheral effects as well as central nervous system effects in areas of the brain remote from the hindbrain would also be expected to contribute to cocaine’s overall effects. In contrast, the effects of the pyrolysis products appeared to be mediated at a site remote from the hindbrain since both the vertebral and i.v. routes of administration produced comparable effects. The respiratory stimulation produced by the pyrolysis products might initially counteract the respiratory depressant effects of cocaine, but any such effect would diminish with subsequent administration due to the acute tolerance observed with the cocaine pyrolysis products. Acknowledgments appeared in abstract form in L. Harris L (ed), Problems of Drug NIH, Rockville MD (1994) and Sot. Neurosci. Abst. 19: 1865, 1993. Animals were maintained in facilities fully accredited by the American Association for the Accreditation of Laboratory Animal Care (AAALAC) and all experimentation was conducted in accordance with the guidelines of the Institutional Care and Use Committee of the Addiction Research Center and the Guide for Care and Use of Laboratory Animals. A preliminary
Dependence
report
1993, 318,
References 1.
M. AMIN, G. GABELMAN, 1437 (1990).
J. KARPEL
and P. BUTTRICK,
Am. J. Cardiol. 66 1434-
1868
2.
3. 4. :. 7: 8. 9. 10. 11. 12.
13. 14. 15. 16. 17. 18. 19.
20. 21. 22. z* 25: 26. 27. 28.
Cocaiie on Hindbrain
Vol. 57, No. 20, 1995
J.M. ISNER, N.A.M.I. ESTES, P.D. THOMPSON, M.R. COSTANZO-NORDIN, R. SUBRAMANIAN, G. MILLER, G. KATSAS, K. SWEENEY and W.Q. STURNER, N. Engl. J. Med. 315 1438-1443 (1986). H.K. ERZOUKI, I. BAUM, S.R. GOLDBERG and C.W. SCHINDLER, J. Cardiovas. Pharmacol. 22 557-563 (1993). J. AMBRE, J. Anal. Tox. 2 241-245 (1985). E.J. CONE, M. HILLSGROVE and W.D. DARWIN, Clin. Chem. a 1299-l 305 (1994). B.R. MARTIN, L.P. LUE and J.P. BONI, J. Anal. Tox. 13 158-162 (1989). P. JACOB, E.R. LEWIS, B.A. ELIAS-BAKER and R.T. JONES, J. Anal. Tox. 14 353-357 (1990). P. JACOB, R.T. JONES, N.L. BENOWITZ, A.T. SHULGIN, E.R. LEWIS and B.A. ELIAS-BAKER, Clin. Tox. 28 121-125 (1990). A.H. NEWMAN, A.C. ALLEN, J.M. WITKIN, S. IZENWASSER, D. MASH and J.L. KATZ, Medicinal Chem. Res. 4 93-l 10 (1994). J.F. CASALE and J.M. MOORE, J. Pharm. Sci. 83 1186 (1994). G.W. HIME, W.L. HEARN, S. ROSE and J. COFINO, J. Anal. Tox. 13 241-245 (1991). V.F.C. RACZKOWSKI, Y.M. HERNANDEZ, H.K. ERZOUKI, T.P. ABRAHAM& A.K. MANDAL, P. HAMOSH, E. FRIEDMAN, J.A. QUEST, K.L. DRETCHEN and R.A. GILLIS, J. Pharmacol. Exp. Ther. 257 51 l-519 (1991). S.R. TELLA, G.R. KORUPOLU, C.W. SCHINDLER and S.R. GOLDBERG, J. Pharmacol. Exp. Ther. m 936-946 (1992). R.D. WILKERSON, J. Pharmacol. Exp. Ther. 246 466-47 1 (1988). P.A. VAN ZWIETEN, Prog. Pharmacol. 1 l-63 (1975). J.W. SHEK, G.Y. WEN and H.M. WISNIEWSKI, Atlas of the rabbit brain and soinal cord, Karger, New York (1986). L. WILKENSON, SYSTAT: Statistics. Version 5.2 editon, SYSTAT Inc., Evanston, IL (1992). D.A. BARBER and R.L. TACKETT, Life Sci. 51.1269-1276 (1992). C.W. SCHINDLER, J.-W. ZHENG, S.R. TELLA and S.R. GOLDBERG, Problems of Drue Denendence 1992, L. Harris (Ed), 367, U. S. Government Printing Office, Washington, D. C. (1993). T.P. ABRAHAMS, W.L. REED, Z. ZHANG and K.J. VARNER, Sot. Neurosci. Abst. Is 723 (1992). W.L. HEARN, D.D. FLYNN, G.W. HIME, S. ROSE, J.C. COFINO, E. MANTEROATIENZA, C.V. WETLI and DC. MASH, J. Neurochem. 56 698-701 (1991). J.L. KATZ, P. TERRY and J.M. WITKIN, Life Sci. 50 1351-1361 (1992). M.C. RITZ, E.J. CONE and M.J. KUHAR, Life Sci. 46 635-645 (1990). W.J. CRUMB and C.W. CLARKSON, J. Pharmacol. Exp. Ther. 261910-917 (1992). T.L. SMITH, M. CALLAHAN, D. WILLIAMS and S.I. DWORKIN, J. Cardiovas. Pharmacol. 21272-278 (1993). R.K. JAIN, M.K. JAIN, L.C. BACHENHEIMER, M.S. VISNER, P. HAMOSH, C.M. TRACY and R.A. GILLIS, J. Pharmacol. Exp. Ther. 252 147-153 (1990). H.A.N. EL-FAWAL and R.W. WOOD, Problems of Drug Denendence 1993, L. Harris (Ed), 261, NIH, Rockville, MD (1994). L.C. CHEN, R.W. WOOD, M.H. ZHONG, J.F. GRAEFE and J. SHOJAIE, Problems of Drug Denendence 1993, L. Harris (Ed), 320, NIH, Rockville, MD (1994).
Pergamon 0024-3205(95)02166-3
EFFECTS OF COCAINE, COCAINE METABOLITES AND COCAINE PYROLYSIS PRODUCTS ON THE HINDBRAIN CARDIAC AND RESPIRATORY CENTERS OF THE RABBIT H. K. Erzouki, A. C. Allen, A. H. Newman, S. R. Goldberg and C. W. Schindler Preclinical
Pharmacology Laboratory, NIH/NIDA Division of Intramural Research, Addiction Research Center, P.O. Box 5 180, Baltimore, MD 2 1224 (Received in final form September 8, 1995)
Summarv Hemodynamic and respiratory effects of vertebral artery or i.v. administration of cocaine, cocaine metabolites and cocaine pyrolysis products were measured in anesthetized rabbits. Vertebral artery administration of 1 mg of cocaine produced decreases in blood pressure and heart rate and respiratory arrest. Cocaethylene (1 mg), a cocaine metabolite produced following co-administration of cocaine and ethanol, had comparable effects except that the respiratory arrest following cocaethylene had a longer duration of action than did cocaine. A decrease in blood pressure was also observed following 1 mg of norcocaine; however, unlike cocaine, norcocaine did not affect respiration. Acute tolerance was not observed to any of the effects of 1 mg of cocaine, cocaethylene or norcocaine following vertebral artery administration. None of these compounds had significant effects following i.v. administration of the same dose. The cocaine metabolites benzoylecgonine and ecgonine methyl ester were without effect by either route in doses up to 3 mg. In contrast to cocaine, the cocaine pyrolysis products anhydroecgonine methyl ester (3 mg) and noranhydroecgonine methyl ester (3 mg) produced similar effects via both routes of administration. Both compounds produced decreases in blood pressure and heart rate and an increase in respiratory rate. Anhydroecgonine ethyl ester (3 mg), a metabolite hypothetically formed from the cocaine pyrolysis product in individuals co-administering ethanol, had effects similar to the other pyrolysis products, although its effects were not as prominent via the i.v. route of administration. Acute tolerance was observed upon administration of the cocaine pyrolysis products. These results indicate that the cocaine pyrolysis products do not share a common mechanism of action with either cocaine or the cocaine metabolites. Key Words: cocaine, cocaine metabolites, cocaine pyrolysis products, hindbrain, cardiac center, respiratory center ‘l‘he cardiac and respiratory
complications following cocaine administration often arise hours after cocaine administration (1,2) when cocaine blood levels would be low or undetectable. This suggests a role for cocaine metabolites in these effects as many of the metabolites have Because of their long half-lives, a half-lives that are much longer than that of cocaine. progressive increase in the level of these metabolites would also be expected following repeated dose “bingeing” as often occurs with cocaine abuse. In addition, cocaine is frequently used in the form of smoked “crack” cocaine. When cocaine is smoked a variety of cocaine pyrolysis products are produced. These compounds might also be expected to contribute to cocaine’s Corresponding Author: Hashim K. Erzouki, Preclinical NIH/NIDA/DIR, PO Box 5180, Baltimore, MD 21224
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overall effects. Further, while early reports seemed to indicate that the metabolites had few effects, there have been recent reports of significant effects of many of the metabolites, including effects on the cardiovascular system (3). Under normal circumstances, cocaine is metabolized to benzoylecgonine and ecgonine methyl ester (EME), with lesser amounts of norcocaine and a variety of other metabolites appearing following all routes of administration. For example, following i.v. administration, the urinary excretion levels of both benzoylecgonine and EME quickly exceed those of cocaine and account for up to 90% of recovered cocaine products from urine (4). Similar results are found following “crack” cocaine smoking. Levels of norcocaine following crack smoking are approximately methyl ester (AEME) results from the one-tenth those of cocaine itself (5). Anhydroecgonine elimination of benzoic acid from cocaine under the high temperature conditions of pyrolysis. AEME has been documented to be the major volatile pyrolysis product formed under free-base cocaine smoking conditions (6). AEME has also been detected in research subjects who smoked cocaine (5) with most subjects excreting substantial amounts of AEME averaging approximately half the molar amounts of cocaine excreted during a 48hr collection period (7,8). The other potential cocaine pyrolysis products evaluated for this report (anhydroecgonine ethyl ester, AEEE; and noranhydroecgonine methyl ester, NAEME) have not been as extensively characterized, however, their formation is likely due to metabolic and pyrolysis processes that are know to occur with cocaine (9). When cocaine administration and alcohol consumption overlap, the novel metabolite cocaethylene is produced in viva. Cocaethylene also has been found as an impurity of both pharmaceutical and illicit cocaine manufacture (10). In human postmortem blood, concentrations of cocaethylene have been reported to nearly equal those of cocaine itself (11). The purpose of the current study was to characterize the effects of cocaine and its metabolites and pyrolysis products on cardiac and respiratory activity. While the hemodynamic effects of cocaine have been extensively documented, its effects on the respiratory system have been studied less extensively. Available data suggest that cocaine’s primary site of action on respiratory function is in the hindbrain, most probably the ventrolateral medulla (12). Since both cardiovascular and respiratory effects of cocaine are thought to play a large role in cocaine toxicity (13), the focus of the current study was on the cardiovascular and respiratory effects of cocaine administered to the hindbrain of the rabbit by way of vertebral artery administration. The use of this procedure required experiments to be performed in anesthetized animals. While anesthesia can blunt the sympathomimetic effects of cocaine on cardiovascular function (14), previous research has shown that the use of anesthesia does not affect the hindbrain response to cocaine (12). Thus, the use of anesthesia allows the determination of the isolated hindbrain response to cocaine with minimal influences of other brain areas. Methods Studies were conducted in anesthetized adult rabbits, of both sexes, which ranged in weight from 2.5 to 3.5 kg. They were anesthetized with sodium pentobarbital (30-35 mgkg, iv.). A longitudinal incision was made in the neck region overlying the trachea and the trachea was exposed, cannulated and connected to a respiratory monitor (MicroSpan 9090-A, Biochem). Respiratory activity was monitored for Animals were allowed to breathe spontaneously. respiratory rate and partial pressure of CO2 (expired, end-tidal C02). If breathing stopped following drug administration, the animals were immediately placed on artificial ventilation. Artificial ventilation was carried out using a respiratory frequency of 40-60 and a tidal volume of 15 cc. These parameters were adjusted to maintain a constant blood pH. Thereafter, the respirator was turned off every 5- 10 min to determine whether respiration had recovered. Body temperature was maintained between 37.0 and 38.OoC (rectal) by an electric heating pad. The femoral artery was cannulated with polyethylene tubing (PE 160) which was filled with heparinized saline (10 USP units/ml). This arterial catheter was connected to a blood pressure transducer (T42-20, Coulboum Instruments, Lehigh Valley, PA). The transducer was connected to an associated amplifier (S72-25, Coulbourn) and blood pressure processor (S77-34, Coulbourn). The blood pressure processor analyzed the raw transducer signal, giving analog
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outputs of systolic (SP), diastolic (DP) and mean pressure (DP + [(SP - DP)/31) after each cardiac cycle. The signal for the end of the cardiac cycle was fed into an Apple IIe computer. For each cycle the computer measured time between cycles with a resolution of 1 msec and read the analog signals for pressure with a resolution of 1 mm Hg. These values were summed and averaged over periods of 30 set for subsequent analysis. The transducer was routinely calibrated manually with a manometer and adjusted to maintain the 1 mm Hg accuracy and linearity over a range of approximately 50 to 250 mm Hg. Lead II of a surface EKG (speed 100 mm/set) was routinely monitored and heart rate was calculated from the EKG tracing. To administer drug to the hindbrain areas, the standard technique of vertebral artery administration was used. For vertebral artery drug administration, a retrograde cannulation of the axillary artery was performed. The tip of the cannula was positioned at the bifurcation of this vessel with one vertebral artery after ligating the cervical, thyrocervical and internal mammary arteries (15). When drug injections were carried out, the vertebral artery was briefly clamped between the bifurcation and the heart. The clamp was removed after injection of a bolus dose of the drug, thus allowing the flow of blood to deliver drug to the hindbrain. For comparison the femoral vein was cannulated and identical doses were also administered intravenously. As less than one-fourth of a intravenously administered dose of cocaine would be expected to reach the brain, and a considerably smaller amount would be expected to reach the hindbrain, any difference in effect observed between i.v. and vertebral artery administration can be attributed to a difference in the amount of the drug reaching the hindbrain. A dose of 1 mg was tested initially for all drugs as preliminary research had shown that for cocaine this dose would produce clear effects in the hindbrain with little or no effect following systemic administration, If no clear effect was observed following 1 mg via the vertebral artery route, the dose was increased up to 3 mg. A fixed dose was used because the total brain weight for rabbits varying in weight from 2.5-3.5 kg varies less than 20% and is not clearly correlated with body weight (16). Drugs. The drugs used were cocaine hydrochloride (NIDA, MW 340), cocaethylene hydrochloride (RBI, Natick MA, MW 354), benzoylecgonine (Sigma Chemical, St. Louis, MW 289) norcocaine hydrochloride (RBI, MW 326), ecgonine methyl ester mesylate (Sigma, MW 236) and sodium pentobarbital (Sigma). Anhydroecgonine methyl ester (AEME, MW ISI), noranhydroecgonine methyl ester (NAEME, MW 167), and anhydroecgonine ethyl ester (AEEE, MW 18 1) were prepared by A. A. as described elsewhere (9). All drugs were dissolved in saline and injected in a volume of 0.25 ml. Doses are as the salt where appropriate. Data Analysis. Baseline values for all measures were taken 10, 5 and 2.5 min prior to drug administration. All drug effects reported are the peak effect observed which typically occurred within 2-7 min after drug administration. Data for each compound were analyzed with a twoway repeated measures analysis of variance (ANOVA), with one repeated measures factor (baseline versus peak effect) and one grouping factor (route of administration). Data on repeated dose effects were analyzed with a one-way (injection number) repeated measures ANOVA. Follow-up contrasts were used to determine individual effects (17). Results Cocaine (1 mg) administered into the vertebral artery resulted in decreases in both arterial blood pressure and heart rate, and also produced respiratory arrest (Table 1). The decreases in pressure and heart rate occurred within 1 min of the injection and peaked within 2 to 5 min. The time course for respiratory arrest was similar. Blood pressure, heart rate and respiration remained depressed to well below pre-drug values for lo-15 min, with recovery to baseline occurring 30-45 min following cocaine administration. In contrast to vertebral artery administration, i.v. administration of 1 mg cocaine had no significant effect on any of the parameters measured. With cocaethylene (Table 1), the profile of hemodynamic effects was similar to that of cocaine, although the effects were smaller. Blood pressure was clearly reduced following vertebral artery administration and there was a tendency for heart rate to be decreased. Respiratory arrest As with cocaine, i.v. administration of also occurred following cocaethylene administration.
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TABLE 1 EFFECTS OF COCAINE AND ITS METABOLITES ON HEMODYNAMIC AND RESPIRATORY ACTIVITY (N=6) DRUG/ ROUTE
MBP
COC VA
BASELINE VALUES HR RR
CO2
MBP
33+1
-25+4**
67+8
183+18
24&3
cot IV _ _ _ _78~7 _cE_vA_ 56&-
183@
23&3
-l?&lO-
39g - - ;6+2- - -3?+2-
CE IV -Nc-v?A-
79$ - - - -80+8-
200+10 -2ijlfi2-
2,+ - ‘21_
NC IV -BE-Vi-
36+2 204$3 25&2 79+ - - - 74+10- -l&l l- - - :6+3- - -3-&2-
1889 BE IV _E;ME_vA_ _ _ _ 84&8 _ 83+4- -28&O92+5
EME IV
39$3 - -4i+2-
4011 2l$l - - 34+3- - -2;+2-
313+13
37*3
31+3
PEAK CHANGES HR RR -28+6**
CO2
-24+3**
5+2 123 523 ----=-----_-. - --19~2~*: --i2&3 -2&_2** 4&4 - X5&4;*
- - -l+l1+4
-l+l 2+1
26&2_5 5*1* O&l - &3- - - 2+1- - --i+l-
2$4 225 3*1 - - -2+3- - - -4_+4 - - -2ki -l&2
13+3**
O+_l - - &l-
11+0
021 O&l - - -3+2- - - 12+1- - - 2+2-15+12
l+l
o+o
Note: Doses are 1 mg. Values are mean + SEM. Peak changes are from baseline. *p<.O5, **p<.Ol from baseline for individual drug and route. MBP=mean blood pressure (mm Hg), HR=heart rate (beats/min), RR=respiratory rate, COC=cocaine, CE=cocaethylene, NC=norcocaine, BE=benzoylecgonine, EME= ecgonine methyl ester, VA=vertebral artery, IV=intravenous.
TABLE 2 EFFECTS OF COCAINE AND THE PYROLYSIS PRODUCTS ON HEMODYNAMIC AND RESPIRATORY ACTIVITY (N=6) BASELINE VALUES RR HR
DRUG/ ROUTE
DOSE
MBP
COC VA
1
67&8
183+18
24+3
CO2
MEW
33+1
-25+4**
PEAK CHANGES RR HR -2&6**
-24k3 **
CO2 13+3**
5+2 -121 183H_ 2$3 1 78kz 39+4 l&3_ 5+3_ - 3- - 91+4 - 206+16 - -24+3 - -3”” - --i2+5 ;+--i&3 - - ii+2 - - 4+2- 8+35+ -7+ - - I+ -15;3 84+5 222&7_ 24-q AEMElV 3 32*1 AEEkiA- ‘j- - &$ - -2:0+8 - 22+2 - >7+2 - - -7fL - --i&3- ;; iI--*’ --8+3- -13”3_ 5+2 -2&2 189&_ AEEEIV 3 32’ 2+7_ 68$ 2;_’ 3- - -85+6 - 214+20 - -22+4 - -32+2 - --i7+6 - - -2&-5 - - -9;; - - -2+2- _24+5l++ 7+1 32+3 78+4 203+5 20+5 NAEMEIV 3 -5Zk3 - I++ _9+2 **
cot IV AEM;+A-
-$&&-A-
-‘0”1
I++ 1
I+
I++
Note: Doses are in mg. Values are mean + SEM. Peak changes are from baseline. *p<.O5, **p<.Ol from baseline for individual drug and route. +p<.O5, ++p<.Ol from baseline for individual drugs where the route factor was not significant. See Table 1 for abbreviations except AEME=anhydroecgonine methyl ester, AEEE= anhydroecgonine ethyl ester, NAEME=noranhydroecgonine methyl ester.
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cocaethylene had little effect except for a small rise in respiratory rate. In contrast to both cocaethylene and cocaine, vertebral artery administration of 1 mg norcocaine (Table 1) had no effect on respiration, although a clear decrease in blood pressure was noted. Again, i.v. The time course for the effects for administration of norcocaine was without effect. cocaethylene and norcocaine were similar to cocaine, except that the respiratory depressant effect of cocaethylene lasted up to 40-60 min following administration and did not recover during the duration of the experiment in 2 of the 6 rabbits. Neither 1 mg benzoylecgonine nor ecgonine methyl ester (Table 1) had any effects by either the vertebral or i.v. routes. As a result, we also administered both compounds at a higher dose (3 mg), but again no significant effects were observed (vertebral artery change scores for 3 mg BE, MBP -1 + 1, HR 1 & 5, RR 2 +2,C02lrf:1;3mgEME,MBP4+l,I-IR1+1,RR5+5,C02 +l>. To test for acute tolerance, after the first injection of cocaine or norcocaine and once all measures had returned to baseline (usually in about 45 min), an additional 1 mg dose of the drug was administered via the vertebral artery; after an additional period of time was allowed for measures to again return to normal (again, about 45 min), a third 1 mg dose was administered. Figure 1 shows the respiratory depressant effect of cocaine following its initial administration and following the two subsequent administrations. Clearly, the respiratory depressant effects were as prominent after the second and third administrations as after the first. For the other effects of both cocaine and norcocaine, these subsequent administrations produced effects that were always comparable to the initial vertebral artery administration. With cocaethylene it was not always possible to administer additional doses, since in some animal’s respiration never recovered to baseline. In those animals in which baseline values recovered to baseline, subsequent vertebral artery administrations of cocaethylene had comparable effects to its initial administration.
-10 -
COCAINE
1
2
3
CONSECUTIVE COCAINE ADMINISTRATIONS
Fig. 1 Effects of cocaine and AEME on respiratory rate following vertebral artery administration. Subsequent administration of drugs (injections 2 and 3) were each given once respiratory rates returned to baseline following the previous administration (usually in about 45 min). Values are mean changes from baseline + S.E.M. *p < .05 from baseline. +p < .05 from injection #l.
l&i6
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In table 2 the results with the cocaine pyrolysis products (AEME, NAEME, AEEE) are presented. For comparison, the results with cocaine are also presented. Preliminary work with doses of 1 or 2 mg of these compounds indicated they produced no significant effects via the vertebral artery route. However, vertebral artery administration of a 3 mg dose of all three of these compounds (AEME, NAEME, AEEE) produced decreases in blood pressure and heart rate similar to those seen with cocaine (Table 2); the onset of these effects were within 2-4 min, with the peak effect occurring 5-7 min after administration and a duration of 20-30 min. In contrast to cocaine, all three compounds increased respiratory rate. The onset of this effect was immediate. Also in contrast to cocaine, i.v. administration of AEME and NAEME produced This was also true for AEEE on heart effects comparable to vertebral artery administration. rate, but not on blood pressure or respiration. The time course for the effects following i.v. administration of AEME, NAEME or AEEE was similar to that following vertebral artery administration. For blood pressure, heart rate and respiratory rate, route of administration was not a significant factor (i.e., only the main effect for drug was significant following the ANOVA analysis). As with cocaine, once the measures had returned to baseline (usually in about 45 min), additional doses of the drugs were administered. In contrast to cocaine, subsequent administrations of the pyrolysis products failed to produce clear changes in any of the parameters measured. Figure 1 shows the results with AEME on respiratory rate following vertebral artery administration. Initially, AEME increased respiratory rate by approximately 12 breaths/mitt, however, increases in respiratory rate were much smaller following the second and third administrations.
Discussion The hemodynamic effects of cocaine following vertebral artery administration in the present study are consistent with other studies of central administration of cocaine in anesthetized animals. Raczkowski et al. (12) reported a similar decrease in blood pressure and heart rate following vertebral artery administration of cocaine in the cat, and Barber and Tackett (18) reported similar effects in the rat following i.c.v. administration of cocaine. Raczkowski et al. (12) also reported respiratory depressant effects of cocaine following vertebral artery administration, although they observed effects on tidal volume and not respiration rate. The fact that i.v. administration of the same dose of cocaine failed to have significant effects, suggests that the effects of cocaine administered through the vertebral artery were mediated primarily in the hindbrain of the rabbit, and not at a more remote central or peripheral site. The profile of hemodynamic effects of cocaethylene in the present study was similar to that of cocaine. This similarity in effect is consistent with previous work using systemic administration of this compound (19,20). However, the respiratory depressant effect of cocaethylene was of longer duration than that of cocaine, which may account for the finding that cocaethylene is slightly more potent than cocaine in terms of lethality (21,22). Unlike cocaine and cocaethylene, norcocaine did not produce respiratory depression. The reason for the discrepancy between the two compounds in producing respiratory depression is unclear. Norcocaine has comparable potency to cocaine for binding to both the DA and NE transporters, although norcocaine is approximately 5 times more potent than cocaine for binding to the 5HT transporter (23). In addition, both cocaine and norcocaine are potent local anesthetics (24). Like cocaine, norcocaine had differential effects via the vertebral versus the i.v. route, again suggesting that its effects following vertebral artery administration are mediated in the hindbrain. Neither benzoylecgonine nor ecgonine methyl ester produced any significant effects when administered through the vertebral artery, which may reflect the fact that neither of these compounds are potent local anesthetics (24). Acute tolerance was not observed over three successive vertebral artery administrations with cocaine, cocaethylene or norcocaine. This is in contrast to previous results with i.v. administrated cocaine in rats (25) and cats (26). While this discrepancy may be due to the species of animal used, it more likely results from the route of administration. Nevertheless, it is possible that the failure to observe acute tolerance to the hindbrain effects of these compounds may well hinder the development of acute tolerance even following i.v. administration.
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The spectrum of effects for the pyrolysis products of cocaine were clearly different from that of cocaine itself. The pyrolysis products produced small increases in respiratory rate rather than the clear decrease observed with cocaine. This small increase in respiratory rate might be expected to counteract the respiratory depressant effect of cocaine. However, as acute tolerance was observed for the respiratory stimulant effect of the pyrolysis products, but not for the respiratory depressant effect of cocaine, this counteracting effect would be short-lived. In addition, the pyrolysis products generally produced comparable changes following both i.v. and vertebral artery administration, suggesting that their effects were not mediated in the hindbrain, but at a more remote central site or in the periphery. Thus, even when the pyrolysis products were producing comparable effects to cocaine, such as on blood pressure and heart rate, it is likely that these effects were mediated at different sites and perhaps through different receptor mechanisms. While little evidence is available on the mechanisms of action for the cocaine pyrolysis products, what evidence is available is consistent with the present findings suggesting that the effects of the pyrolysis products are mediated through different mechanisms than for cocaine. Newman et al. (9) reported that none of the pyrolysis products bind to cocaine recognition sites on the dopamine transporter in rat caudate-putamen, nor do they produce behavioral or toxicological effects comparable to cocaine. In addition, these drugs also do not bind with appreciable affinity to either brain muscarinic or nicotinic receptors. El-Fawal and Wood (27) did observe an anticholinergic effect of AEME when tested in vitro. This group (28) also observed bronchoconstriction and decreases in body temperature when AEME was given into the lung, but not when it was given i.v., suggesting that the effect may have been due to local lung irritation. Therefore, it is unclear how these drugs produced their effects in the present study. The observation that the effects of the pyrolysis products do not appear to be mediated in the hindbrain, suggests mediation in the periphery where different receptor systems may be involved. In summary, the present results indicate that both cocaine and cocaethylene act in the hindbrain of the rabbit to decrease blood pressure, heart rate and respiration rate. Cocaethylene had a longer duration of action than cocaine in depressing respiration. In addition, there was no acute tolerance to the hindbrain effects of these drugs. Norcocaine also acted in the hindbrain to decrease blood pressure. Following systemic administration at doses high enough to reach hindbrain concentrations similar to those observed here, these hindbrain effects of both cocaine and its metabolites would certainly be expected to contribute to the overall effect of cocaine. Of course, at these higher doses peripheral effects as well as central nervous system effects in areas of the brain remote from the hindbrain would also be expected to contribute to cocaine’s overall effects. In contrast, the effects of the pyrolysis products appeared to be mediated at a site remote from the hindbrain since both the vertebral and i.v. routes of administration produced comparable effects. The respiratory stimulation produced by the pyrolysis products might initially counteract the respiratory depressant effects of cocaine, but any such effect would diminish with subsequent administration due to the acute tolerance observed with the cocaine pyrolysis products. Acknowledgments appeared in abstract form in L. Harris L (ed), Problems of Drug NIH, Rockville MD (1994) and Sot. Neurosci. Abst. 19: 1865, 1993. Animals were maintained in facilities fully accredited by the American Association for the Accreditation of Laboratory Animal Care (AAALAC) and all experimentation was conducted in accordance with the guidelines of the Institutional Care and Use Committee of the Addiction Research Center and the Guide for Care and Use of Laboratory Animals. A preliminary
Dependence
report
1993, 318,
References 1.
M. AMIN, G. GABELMAN, 1437 (1990).
J. KARPEL
and P. BUTTRICK,
Am. J. Cardiol. 66 1434-
1868
2.
3. 4. :. 7: 8. 9. 10. 11. 12.
13. 14. 15. 16. 17. 18. 19.
20. 21. 22. z* 25: 26. 27. 28.
Cocaiie on Hindbrain
Vol. 57, No. 20, 1995
J.M. ISNER, N.A.M.I. ESTES, P.D. THOMPSON, M.R. COSTANZO-NORDIN, R. SUBRAMANIAN, G. MILLER, G. KATSAS, K. SWEENEY and W.Q. STURNER, N. Engl. J. Med. 315 1438-1443 (1986). H.K. ERZOUKI, I. BAUM, S.R. GOLDBERG and C.W. SCHINDLER, J. Cardiovas. Pharmacol. 22 557-563 (1993). J. AMBRE, J. Anal. Tox. 2 241-245 (1985). E.J. CONE, M. HILLSGROVE and W.D. DARWIN, Clin. Chem. a 1299-l 305 (1994). B.R. MARTIN, L.P. LUE and J.P. BONI, J. Anal. Tox. 13 158-162 (1989). P. JACOB, E.R. LEWIS, B.A. ELIAS-BAKER and R.T. JONES, J. Anal. Tox. 14 353-357 (1990). P. JACOB, R.T. JONES, N.L. BENOWITZ, A.T. SHULGIN, E.R. LEWIS and B.A. ELIAS-BAKER, Clin. Tox. 28 121-125 (1990). A.H. NEWMAN, A.C. ALLEN, J.M. WITKIN, S. IZENWASSER, D. MASH and J.L. KATZ, Medicinal Chem. Res. 4 93-l 10 (1994). J.F. CASALE and J.M. MOORE, J. Pharm. Sci. 83 1186 (1994). G.W. HIME, W.L. HEARN, S. ROSE and J. COFINO, J. Anal. Tox. 13 241-245 (1991). V.F.C. RACZKOWSKI, Y.M. HERNANDEZ, H.K. ERZOUKI, T.P. ABRAHAM& A.K. MANDAL, P. HAMOSH, E. FRIEDMAN, J.A. QUEST, K.L. DRETCHEN and R.A. GILLIS, J. Pharmacol. Exp. Ther. 257 51 l-519 (1991). S.R. TELLA, G.R. KORUPOLU, C.W. SCHINDLER and S.R. GOLDBERG, J. Pharmacol. Exp. Ther. m 936-946 (1992). R.D. WILKERSON, J. Pharmacol. Exp. Ther. 246 466-47 1 (1988). P.A. VAN ZWIETEN, Prog. Pharmacol. 1 l-63 (1975). J.W. SHEK, G.Y. WEN and H.M. WISNIEWSKI, Atlas of the rabbit brain and soinal cord, Karger, New York (1986). L. WILKENSON, SYSTAT: Statistics. Version 5.2 editon, SYSTAT Inc., Evanston, IL (1992). D.A. BARBER and R.L. TACKETT, Life Sci. 51.1269-1276 (1992). C.W. SCHINDLER, J.-W. ZHENG, S.R. TELLA and S.R. GOLDBERG, Problems of Drue Denendence 1992, L. Harris (Ed), 367, U. S. Government Printing Office, Washington, D. C. (1993). T.P. ABRAHAMS, W.L. REED, Z. ZHANG and K.J. VARNER, Sot. Neurosci. Abst. Is 723 (1992). W.L. HEARN, D.D. FLYNN, G.W. HIME, S. ROSE, J.C. COFINO, E. MANTEROATIENZA, C.V. WETLI and DC. MASH, J. Neurochem. 56 698-701 (1991). J.L. KATZ, P. TERRY and J.M. WITKIN, Life Sci. 50 1351-1361 (1992). M.C. RITZ, E.J. CONE and M.J. KUHAR, Life Sci. 46 635-645 (1990). W.J. CRUMB and C.W. CLARKSON, J. Pharmacol. Exp. Ther. 261910-917 (1992). T.L. SMITH, M. CALLAHAN, D. WILLIAMS and S.I. DWORKIN, J. Cardiovas. Pharmacol. 21272-278 (1993). R.K. JAIN, M.K. JAIN, L.C. BACHENHEIMER, M.S. VISNER, P. HAMOSH, C.M. TRACY and R.A. GILLIS, J. Pharmacol. Exp. Ther. 252 147-153 (1990). H.A.N. EL-FAWAL and R.W. WOOD, Problems of Drug Denendence 1993, L. Harris (Ed), 261, NIH, Rockville, MD (1994). L.C. CHEN, R.W. WOOD, M.H. ZHONG, J.F. GRAEFE and J. SHOJAIE, Problems of Drug Denendence 1993, L. Harris (Ed), 320, NIH, Rockville, MD (1994).