Higher levels of nicotine in arterial than in venous blood after cigarette smoking

Drug and Alcohol Depenhe,

33 (1993) 23 - 29 Elsevier Scientific Publishers Ireland Ltd.

23

Higher levels of nicotine in arterial than in venous blood after cigarette smoking Jack E. Henning-field”, June M. Stapleton”, Neal L. Benowitzb, Roger F. GraysonC and Edythe D. Londona aAddiction Research Center, National Institute on Drug Abuse, Baltimore, MD 21224, ‘Clinical Pharmacology Unit of the Medical Service, San Francisco General Hospital, Department of Medicine, Building 30, 5th Floor, 1001 Potrero Avenue, San Francisco, CA 94110 and ‘Department of Anesthesiology, The Johns Hopkins Medical Institutions, 600 N. Wolfe Street, Baltimore, MD 21205 (USA) (Accepted January 21, 1993) We examined differences between arterial and venous concentrations of nicotine in human subjects. Shortly after smoking a cigarette, levels of nicotine in arterial plasma were more than double those in venous plasma. The time course of the rise in arterial nicotine levels and the magnitude of the arteriovenous difference varied considerably among subjects. For some subjects, arterial nicotine concentrations after one cigarette were similar to venous concentrations typically observed after 20 cigarettes and were nearly 10 times greater than venous concentrations. Our findings have implications for understanding the high degree of addictiveness and cardiovascular toxicity of smoked forms of drugs. Key words: nicotine; smoking; arterial

Introduction It is generally assumed that addictiveness of nicotine and cocaine is enhanced when these drugs are self-administered via the smoked route, as when tobacco cigarettes and crack cocaine are used (Russell and Feyerabend, 1978; Perez-Reyes et al., 1982; Jones, 1987; Johanson and Fischman, 1939). The reason has been postulated to be the extremely short time period (estimated at 7-9 s) required for the drug to reach the brain following absorption in the pulmonary alveoli (Benowitz, 1990); drug-laden blood is pumped directly to the brain by the left ventricle of the heart, via the carotid arteries. Drug absorption via inhalation may also contribute to the cardiovascular toxicity of cigarettes and crack cocaine. As the inhaled drug is funneled into the pulmonary veins, blood makComespondence to: Jack E. Henningfield, Clinical Pharmacology Branch, NIDA Addiction Research Center, PO Box 5180 or 4940 Eastern Avenue, Baltimore, MD 21224, USA. 0376~8716/93/$06.00 0 1993 Elsevier Scientific Publishers Printed and Published in Ireland

ing its first pass through the heart, brain, and other organs would contain high concentrations of drug. It has been suggested that arterial concentrations of nicotine should be about ten times higher than systemic venous concentrations (Sachs, 1989). Concentrations of nicotine in arterial blood have been shown to reach levels greater than 30 pgll after a subject smoked one cigarette at a rate of one puff per min (Armitage et al., 1975). The differences between arterial and venous drug concentrations could have implications for understanding the addictiveness and toxicity of smoked drugs. The study by Armitage et al., (1975) involved the collection of arterial blood, but did not collect venous blood, thus precluding estimates of possible differences in arterial and venous blood; nonetheless they concluded that the arterial nicotine concentrations they observed were ‘somewhat higher than those found in venous blood’. Preliminary analysis of data from our laboratories indicated that concentrations of nicotine in arterial blood could substantially Ireland Ltd.

24

exceed those in venous blood following the smoking of a single tobacco cigarette (Henningfield et al., 1990). More recently, Moreyra et al., (1992) compared nicotine in arterial and venous blood samples collected once immediately following the smoking of one cigarette and again immediately following the smoking of a second cigarette. They found substantial arterial and venous differences in nicotine levels at these points. The present report expands on our preliminary report and that of Moreyra et al., (1992) with the addition of more subjects and a more detailed analysis of the early kinetics of nicotine in arterial and venous blood following the smoking of a single cigarette. Methods A study of the effects of cocaine on regional cerebral glucose metabolism utilizing positron emission tomography (PET) scanning techniques required insertion of venous and arterial catheters in human volunteers (London et al., 1990). The present research protocol was conducted as a supplemental study to the PET protocol, utilizing the opportunity to determine the early arteriovenous drug kinetics in a manner that exposed the volunteers to little additional risk or discomfort. The study was approved by the Institutional Review Boards of The Johns Hopkins Medical Institutions. Informed consent to participate in the study was provided by the volunteers, who were paid for their participation. Procedure Subjects were polydrug abusers in good health. Eight men with a mean age of 33.6 years (range = 26-43) who smoked a mean of 22.7 cigarettes per day (range = 10-40) had been deprived of tobacco for 5 - 8 h at the time of this study. Blood sampling began about 2.5 to 3 h after they had received an i.v. injection of 2 ml of 0.9% NaCl (saline) containing 40 mg cocaine HCl (n = 3) or the same volume of saline placebo (n = 5). This study was conducted on the day of the first of two PET scans, at about 0.5 h after completion of the PET scan. Blood samples were taken from the radial artery in one arm

and a vein in the opposite arm, usually the antecubital vein. Arterial and venous blood samples were drawn before smoking a cigarette, and at 5 - 6 min and 10 - 11 min after the cigarette was lighted (approximately 1 and 5 min after the cigarette was extinguished). For each time point, collection was begun simultaneously from the arterial catheter and from an intravenous catheter in the opposite arm. Because of the pressure in the arterial catheter, sampling was usually completed about 20 s earlier from the arterial than from the venous catheter. Time required to draw a sample averaged about 15 s for arterial sampling and about 35 s for venous sampling. Two subjects had additional samples drawn at 1 and 3 min after light-up, one subject was also sampled at 3 min after light-up, and one subject at 8 and 12 min after light-up. Each subject smoked one of his usual brand of cigarettes over a period of approximately 5 min. All subjects smoked filter-tipped cigarettes. Four subjects smoked mentholated cigarettes (Kool, Newport), and four smoked nonmentholated cigarettes (Marlboro, Pall Mall, Camel). Subjects were instructed to smoke in their usual way. Blood samples (5 ml each) were transferred to vacutainers containing 20 mg potassium oxalate, and were placed immediately on ice. Later the same day, they were centrifuged, and the plasma was stored at - 70°C for subsequent analysis of nicotine and cotinine concentrations by capillary gas chromatography (Jacob et al., 1981). This assay has a sensitivity of 1 ng nicotine per ml and a mean coefficient of variation of 4.5%. Statistical analysis Statistical analyses were performed using Analysis of Variance (BMDP 4V) with GreenhouseGeisser correction for repeated measures, ttests (BMDP 3D), and Pearson correlations (BMDP 6D) with P c 0.05 used as the criterion of statistical significance (Dixon et al., 1988). Results Concentrations of nicotine in arterial and venous plasma samples from each of the eight

25 Table I.

Concentrations

Subject Number

Baseline

of nicotine in arterial and venous plasma (ng/ml). 1 min

A

V

6.5 6.4 3.8 4.8 4.2 3.0 5.0 3.6

8.4 8.3 5.4 3.9 6.2 7.1 8.0 5.8

A

3 min A

V -

-

87.1 78.0 54.0

9.3 6.4

42.9 64.4

5 min

10 min

V

A

V

A

V

-

66.7 45.8 43.7 44.0 30.1 48.2 92.5 49.8

18.2 26.6 43.1 30.3 22.9 15.7 12.7 16.0

32.6 33.0 30.5 22.9 18.3 32.0 50.9 24.5

19.9 16.2 32.3 23.2 16.3 14.9 16.6 13.3

13.1 12.2 14.1

A = arterial sample, V = venous sample. Times shown are from light-up of the cigarette.

subjects are shown in Table I. Smoking one cigarette produced a statistically significant increase in both arterial and venous concentrations of nicotine, but the increase was much greater in arterial blood (Fig. 1). Analysis of variance yielded statistically significant main effects for sampling site [F&7) = 9.37, P < 0.021 and time of sampling [F(2,6) = 125.15, P < O.OOOl]and a significant interaction of site by time [F(2,6) = 4.99, P c 0.011. t-Tests indicated that arterial levels were higher than venous levels at both 5 and 10 min after light-up, although

*

SASEL INE

0

ARTERIAL

n

VENOUS

5 TIME

10 AFTER

LIGHT-UP

(mln)

Fig. 1. Arterial and venous nicotine concentrations before and after smoking one cigarette. Mean of 8 subjects. *Arterial differs significantly from venous concentration at that time point, P < 0.05.

arterial levels were significantly lower than venous levels prior to smoking. There was considerable intersubject variability with regard to the difference between arterial and venous concentrations of nicotine at 5- 6 min after light-up, with differences ranging from 0.6 to 79.8 nglml (arterial minus venous). Four subjects showed differences greater than 30 nglml, and four subjects showed differences less than 20 nglml. Pre-smoking arterial and venous nicotine levels were low, as can be seen in Fig. 1. Student’s t-tests comparing post-cigarette to pre-cigarette levels showed statistically significant increases in both arterial and venous levels at 5-6 min and lo- 11 min after smoking. Comparing the two post-smoking time points, arterial nicotine levels were significantly lower at 10 - 11 min than at 5 - 6 min after light-up [t(7) = 5.68, P < O.OOl], and there was a non-significant trend for venous levels to also be lower at the later time point [t(7) = 2.12, P < 0.081. For the three subjects who had samples drawn at earlier time points, there was considerable individual variability in the time course of the rise of nicotine levels in arterial blood (Fig. 2). Across all eight subjects, there were no statistically significant correlations between arterial and venous nicotine levels prior to smoking (r = 0.53), at 5 min post-light-up (r = -0.52) or at 10 min post-light-up (r = -0.06). Student’s t-tests comparing post-cigarette to

26

100

1 INDIVIDUAL

1 !!I

o-

Baseline

SUBJECTS --f+ -Q+ + --c ---li-

I

1

ARTERIAL4ubject 1 ARTERIAL-Subject 2 ARTERIAL-Subject 3 VENOUS-Subject 1 VENOUS-Subject 2 VENOUS-Subject 3

,

3

5

7

9

11

TIMEAFTERLIGHTdP (mln) Fig. 2. Time course of arterial and venous nicotine concentrations

for 3 individual subjects before and after smoking one

cigarette.

pre-cigarette cotinine levels showed no statistically significant increases in venous levels and a small but statistically significant increase at 10 min post-light-up, compared to pre-smoking levels. There was a non-significant trend for both arterial and venous cotinine levels to be higher at 10 - 11 min than at 5 - 6 min after light-up [t(7) = -2.04, P < 0.091. Consistent with these trends in cotinine levels, analysis of variance yielded a statistically significant main effect of sampling time [F(2,6) = 5.00, P < 0.021, with no significant main effect of sampling site (F(1,7) = - 0.58, P > 0.461 and no significant interaction [F(2,6) = 0.93, P > 0.361. t-Tests indicated that there were no statistically significant differences between arterial and venous cotinine levels before smoking or at 5 - 6 min or 10 - 11 min post-light-up. Data analyses performed while omitting the three subjects who had received cocaine earlier that day yielded essentially similar findings. Nevertheless, the subjects that had received cocaine, as a group, showed a tendency to have lower venous nicotine levels before smoking than the subjects that had received placebo

[t(6) = 2.36, P < 0.061. The pattern of arteriovenous differences was similar in the cocaine group and the placebo group. There was no statistically significant effect of cocaine on nicotine levels after smoking as tested by two-way analysis of variance [F&6) = 3.17, P = 0.1251. The cocaine group, however, showed a tendency to have lower arterial nicotine levels after smoking than the placebo group, and this was statistically significant at 10 min post-light-up as tested by a t-test [t(6) = 2.65, P < 0.04). The variables of age, number of cigarettes smoked per day, and hours of smoking deprivation were not significantly correlated with arterial or venous nicotine or cotinine concentrations before smoking. Venous nicotine levels at 5 - 6 min post-light-up showed a statistically significant negative relationship with hours of smoking deprivation (T = -0.737, P < 0.04) and there was a non-significant trend in the same direction at lo-11 min post-light-up (r = -0.625, P < 0.10). Analysis using difference scores (post - pre) yielded slightly stronger correlations (r = -0.755, P < 0.03 at 5 min; r = -0.675, P < 0.07 at 10 min). No such correlations were found for arterial nicotine con-

27

centrations (all r values < 0.20, P values > 0.60). No significant correlations were found between post-smoking nicotine levels and age or number of cigarettes smoked per day. Discussion The present study demonstrates that smoke inhalation produces increases in drug concentration of considerably greater magnitude in arterial plasma than in venous plasma, that the difference between arterial and venous nicotine levels declines rapidly, and that there is considerable variability across subjects in both the magnitude and time course of arterial concentrations. The physiological basis of this effect is that the massive area for capillary drug absorption in the alveoli of the lungs leads to high concentrations of nicotine in the arterial blood stream; concentrations measured in venous blood would be diminished by the amount of drug remaining in various organs and skeletal muscle as well as by the degree to which the drug was diluted into the general circulation (Kety, 1951). In some subjects, the concentrations of nicotine in arterial blood observed in this study after one cigarette were comparable to those observed in venous blood following the smoking of 20 or more cigarettes (U.S. Department of Health and Human Services, 1988). These levels are higher than those reported by Armitage et al. (19’75), possibly due to different patterns of inhalation (e.g., more frequent puffing by our subjects, who were permitted to smoke according to their usual pattern). Although the arterial nicotine blood levels were as much as 10 times greater than those of venous blood, even these arterial levels were probably lower than those produced immediately after puffing. Determination of maximum arterial-venous differences would probably require assessment of arterial and venous blood within 15 s following the first puff. That interval would be sufficient for one transit of blood from the right atrium of the heart to the peripheral arterial circulation, after which arterial and venous blood would then begin begin to mix, thus diluting the arterial concentrations (Kety, 1951).

The Armitage et al., (1975) study also probably missed the undiluted nicotine value because their blood samples were taken during the interval approximately 30- 50 s after each puff. In comparing data from the two studies, it may be helpful to note that, in the present study, our first post-smoking sample was collected at approximately one minute after the final puff. A complete pass of drug through the circulation to the original site of absorption should occur in approximately one minute, at which point a considerable degree of dilution should have occurred. The high arterial concentrations produced by smoke inhalation would be expected to enhance the reinforcing effects of the drug by decreasing the latency from self-administration to central nervous system stimulation, as well as by producing the rapid and transient physiologic perturbation that appears important in the addiction potential of drugs in general. Delivery of high concentrations to the brain may also be necessary to overcome tolerance developed to prior doses of the drug. Conversely, these findings are consistent with the relatively low abuse liability of the polacrilex (gum) and transdermal patch forms of nicotine and the difficulty that some people have in using the gum as a replacement for smoking (U.S. Department of Health and Human Services, 1988; Bunker et al., 1992). As nicotine from polacrilex and transdermal patches is absorbed into the venous circulation, it results in gradually rising concentrations in blood and brain, and would not produce either the high concentrations or the rapid bolus effects produced by smoke inhalation (Sachs, 1989; Palmer et al., 1992). The variation in arterial-venous differences observed across subjects is not explained by differences in baseline nicotine levels, age, or hours of smoking deprivation. It is probably not due to differences among the brands of cigarettes smoked since differences in nicotine content of cigarettes are not reliably related to differences among subjects in nicotine absorption (Benowitz et al., 1983; Benowitz and Jacob, 1984; Gori and Lynch, 1985). A number of factors might contribute to this variability, including depth of inhalation, puff frequency, puff duration, and the

28

timing of each puff with respect to the time of arterial sampling, as well as individual differences in the speed and uniformity of pulmonary drug absorption, and in cardiac output, which determines the extent of mixing in arterial blood prior to sampling. Since we did not know the exact moment at which an arterial bolus passed the sampling site, in most cases we have underestimated the peak arterial concentrations. Since the half-life of cocaine is less than 40 min (Cone et al., 1988), we did not expect to find an effect of cocaine at 2.5 - 3 h after administration. The tendency for the cocaine group to show lower nicotine levels than the placebo group may be an artifact of small sample size. The finding that venous, but not arterial, nicotine levels after smoking one cigarette are negatively related to the number of hours of deprivation before smoking suggests that, at short deprivation times, there may be nicotine remaining in tissues so that the tissues take up less, minimizing arteriovenous differences. In these chronic smokers at long deprivation times, nicotine may be absorbed readily into tissues, leaving relatively lower levels in venous blood. Identifying other sources of individual variability will be important in developing valid mathematical models of arterial blood concentrations after drug inhalation (e.g., Porchet et al., 1987). Such models are desirable because of difficulties in the empirical determination of arterial blood levels. The lack of correlations between arterial and venous nicotine levels at all time points measured suggests that at these early time points venous nicotine levels across subjects may not be a reliable indicator of nicotine concentrations reaching the brain, and would not be expected to correlate well with subjective effects of the drug. For cotinine, on the other hand, at these early time points arterial and venous plasma levels began to rise together, with levels remaining correlated across subjects. It is entirely possible, of course, that these correlations might not be sustained at later time points as cotinine levels continue to rise. Interestingly, nicotine plasma concentrations

determined in the pre-cigarette blood samples revealed that arterial levels were significantly lower than venous levels. Although the magnitude of the difference was small, the effect was consistent, reflecting that small amounts of nicotine sequestered in tissues continue to be released into the blood many hours after smoking the last cigarette. The rapid intravenous and inhalation routes produce high concentrations of drug in the arterial circulation, apparently contributing to the high abuse liability of both routes of drug administration. Inhalation might provide a somewhat more rapid and concentrated bolus, however, because high concentrations of drug enter the pulmonary capillaries after inhalation. By contrast, after i.v. dosing, the drug must move from the peripheral vein to the vena cava to the right side of the heart and then to the pulmonary arterial circulation before reaching the brain. The inhalation route also makes it very convenient for the user to repeatedly administer small doses at frequent intervals. Our data are consistent with pharmacokinetic theories of why a more intense-high results from smoking cocaine as compared to intravenous injection (Jones, 1987; Henningfield et al., 1990). Such concentrated drug boli may also contribute to deaths due to cocaine overdose and other toxic reactions that sometimes are produced by crackcocaine smoking. Thus morbidity and mortality associated with substance abuse is likely to be directly increased by exposure of the heart, brain, and other organs to high concentrations of drug, as well as indirectly by the strong resultant addictions which result in frequent exposure of the user to associated toxins (e.g., carcinogens). Because of the rapid equilibration of drug concentrations between arterial blood and the brain, post-inhalation arterial drug levels should better reflect brain concentrations than peripheral venous levels, which reflect effluent concentrations primarily from skeletal muscle. The present findings suggest that the inhalation route results in exposure of the brain and the heart to much greater drug concentrations than would be predicted based on venous plasma

29

measurements. Such information should be useful by providing researchers using in vitro assays with more accurate information on the concentrations of drug to which biologic tissues are exposed. Conversely, venous blood levels of smoked drugs may greatly underestimate the concentrations to which tissue is exposed. Such underestimation may contribute to the difficulty of explaining some cocaine-induced deaths by postmortem assessment of drug levels in venous blood. Because a decline in peak arterial and differences concentration venous blood presumably begins after the first full pass of arterial blood through the left ventricle of the heart, quantitation of peak differences and the kinetics will require further such studies with collection of blood samples at intervals of 15 - 30 s post-puffing. Acknowledgments The authors wish to thank Elias Shaya, M.D., Barbara Holicky, R.N., and Merrily Smith, R.N. for drawing blood samples; W. Robert Lange, M.D. and Carlo Contoreggi, M.D. for medical coverage, and Gersham Dent, Geraldine Hill, Valerie O’Brien, and Alex Radzius for technical assistance. References Armitage, A.K., Dollery, CT., George, CF., Houseman, T.H., Lewis, P.J. and Turner, D.M. (1975) Absorption and metabolism of nicotine from cigarettes. Br. Med. J. iv, 313-316. Benowitz, N. (1990) Clinical pharmacology of inhaled drugs of abuse: implications in understanding nicotine dependence. Natl. Inst. Drug Abuse Res. Monogr. 99, 12- 29. Benowitz, N.L., Hall, SM., Herning, RI., Jacob, P., III, Jones, R.T. and Osman, A.-L. (1983) Smokers of lowyield cigarettes do not consume less nicotine. N. Engl. J. Med. 309, 1399142. Benowitz, N.L. and Jacob, P., III (1984) Daily intake of nicotine during cigarette smoking. Clin. Pharmacol. Ther. 35, 499 - 504. Bunker, E.B., Pickworth, W.B. and Henningfield, J.E. (1992) Nicotine patch: Effect on spontaneous smoking. Nat\. Inst. Drug Abuse Res. Monogr. 119, 470. Cone, E.J., Kumor, K., Thompson, L.K. and Sherer, N. (1988) Correlation of saliva cocaine levels with plasma

levels and with pharmacologic effects after intravenous cocaine administration in human subjects. J. Anal. Toxicol. 12, 200-206. Dixon, W.J., Brown, M.B., Engelman, L., Hill, M.A. and Jennrich, R.I. (1988) BMDP statistical software manual, University of California Press, Berkeley. Gori, G.B. and Lynch, C.J. (1985) Analytical cigarette yields as predictors of smoke bioavailability. Regul. Toxicol. Pharmacol. 5, 314 - 326. Henningfield, J.E., London, E.D. and Benowitz, N.L. (1990) Arterio-venous differences in plasma concentrations of nicotine after cigarette smoking. J. Am. Med. Assoc. 263, 2049 - 2050. Jacob, P., III, Wilson, M. and Benowitz, N.L. (1981) Improved gas chromatographic method for the determination of nicotine and cotinine in biologic fluids. J. Chromatogr. 222, 61- 70. Johanson, C.E. and Fischman, M.W. (1989) The pharmacology of cocaine related to its abuse. Pharmacol. Rev. 41, 3-52. Jones, R.T. (1987) Psychopharmacology of cocaine. In: Cocaine: A Clinician’s Handbook, (Washton, A.M. and Gold, MS., eds.), pp. 55-72. Guilford Press, New York. Kety, S.S. (1951) The theory and application of the exchange of inert gas at the lungs and tissues. Pharmacol. Rev. 3, 1-41. London, E.D., Cascella, N.G., Wong, D.F., Phillips, R.L., Dannals, R.F., Links, J.M., Herning, R., Grayson, R., Jaffe, J.H. and Wagner, H.N., Jr. (1990) Cocaineinduced reduction of glucose utilization in human brain. A study using positron emission tomography and [fluorine 18lfluorodeoxyglucose. Arch. Gen. Psychiatr. 47, 567 - 574. Moreyra, A.E., Lacy, CR., Wilson, A.C., Kumar, A. and Kostis, J.B. (1992) Arterial blood nicotine concentration and coronary vasoconstrictive effect of low-nicotine cigarette smoking. Am. Heart J. 124, 392-397. Palmer, K.J., Buckley, M.M. and Faulds, D. (1992) Transdermal nicotine: A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy as an aid to smoking cessation. Drugs 44, 498 - 529. Perez-Reyes, M., Di Guiseppi, S., Ondrusek, G., Jeffcoat, A.R. and Cook, C.E. (1982) Free-base cocaine smoking. Clin. Pharmacol. Ther. 32, 459-465. Porchet, H.C., Benowitz, N.L., Sheiner, L.B. and Copeland, J.R. (1987) Apparent tolerance to the acute effect of nicotine results in part from distribution kinetics. J. Clin. Invest. 80, 1466- 1471. Russell, M.A.H. and Feyerabend, C. (1978) Cigarette smoking: A dependence on high-nicotine boli. Drug Metab. Rev. 8, 29 - 57. Sachs, D.P.L. (1989) Nicotine polacrilex: Practical use requirements. Curr. Pulmonol. 10, 141- 157. U.S. Department of Health and Human Services (1988) The health consequences of smoking: Nicotine addiction. DHHS Publication No. (CDC) 88 - 8406.