guanosene 3',5-monophosphate (cyclic GMP) and may play a role in tissue proliferation and tumoregenesis, as well as exert effects on ciliary function and mucosal secretion in lung tissue. Acute lung damage resulting from exposure to nitrogen dioxide at levels of 80 ppm for 3 hours has been reported by Langloss, et al. (28). Blank, et al. (9) exposed rats to levels of 15 to 40 ppm for up to 5 hours. Both of these groups reported alveolar damage with subsequent edema followed by hyperplasia or increased biosynthesis. The relevance of these types of exposure to smoking-related disease processes is unclear, however, since Norman and Keith (34) reported that nitrogen dioxide is present in cigarette smoke only in trace quantities. Little is known about the effects of phenol in smoke. Dalhamn (14), however, administered puffs of smoke from cigarettes with high and low phenol concentrations (18.8 and 2.7 mg/lOO cigarettes versus a "normal" cigarette concentration of 7 mg/lOO cigarettes) and found a clear correlation between ciliostasis and the phenol level in smoke. This area is one that should also be explored in more detail. 14-81 Physiological Responses to Cigarette Smoke: References (1) AHMED, S.S., MOSCHOS, C.B., LYONS, M.M., OLDEWURTEL, H.A., COUMBIS, R.J., REAGAN, T.J., JENKINS, B. Cardiovascular effects of long- term cigarette smoking and nicotine administration. American Journal of Cardiology 37: 33-40, January 1976. (2) ARMITAGE, A.K. Effects of nicotine and tobacco smoke on blood pressure and release of catecholamincs from the adrenal glands. British Journal of Pharmacology 25: 5X-526,1965. (3) ARNOLD, W.P., ALDRED, R., MURAD, F. Cigarette smoke activates guanylate cyclase and increases guanosine 3, 5'-monophosphate in tissues. Science 198: 334-936, December 2,1977. (4) BATTISTA, S.P., GUERIN, MR., GORI, G.B. KENSLER, C.J. A new system for quantitatively exposing laboratory animals by direct inhalation. Archives of Environmental Health 27: 376332, December 1973. (5) BELLET, S., DEGUZMAN, N.T., KOSTIS, J.B., ROMAN, L., FLEISCHMANN, D. The effect of inhalation of cigarette smoke on ventricular fibrillation threshold in normal dogs and dogs with acute myocardial infarction. American Heart Journal 33(l): 67-76, January 1972 (6) BINNS, R., BEVEN, J.L., WILTON, L.V., LUGTON, W.G.D. Inhalation toxicity studies on cigarette smoke. II. Tobacco smoke inhalation dosimetry studies on small laboratory animals. Toxicology 6: 197~206,1376. (n BINNS, R., BEVEN, J.L., WILTON, L.V., LUGTON, W.G.D. Inhalation toxicity studies on cigarette smoke. III. Tobacco smoke inhalation dosimetry study on rata. Toxicology 6: 2(X-217,1976. (8) BINNS, R., CLARK, G.C. An experimental model for the assessment of the effects of cigarette smoke inhalation on pulmonary physiology. Annals of Occupational Hygiene 15: 237247.1972. (9) BLANK, M.L., DALBEY, W., NETI'ESHEIM, P., PRICE, J., CREASIA, D., SNYDER, F. Sequential changes in phospholipid composition and synthesis in lungs exposed to nitrogen dioxide. American Review of Respiratory Disease 117: 273236,1978. (10) BURN, J.H., RAND, M.J. Action of nicotine on the heart. British Medical Journal 1: 137-139, January 18,1953. (11) BURROWS, I.E., CORP, P.J., JACKSON, G.C., PAGE, B.F.J. The determination of nicotine in human blood by gas-liquid chromatography. Analyst 96: 814, January 1971. (12) CAHAN, W.G., KIRMAN, D. An effective system and procedure for cigarette smoking by dogs. Journal of Surgical Research 3(12): 567-575, December 1963. (18) CRAMLET, S.H., ERICKSON, H.H., GORMAN, H.A. Ventricular function following acute carbon monoxide exposure. Journal of Applied Physiology 39(3): 432-436, September 1975. (14) DALHAMN, T. Effect of different doses of tobacco smoke on ciliary activity in cat. Variations in amount of tobacco smoke, interval between cigarettes, content of "tar," nicotine, and phenol. Toward a Less Harmful Cigarette. National Cancer Institute Monograph No. 23. U.S. Department of Health, Education, and Welfare, Public Health Service, National Institutes of Health, National Cancer Institute, 1363, pp. 79-37. (15) DAVIS, B.R., HOUSEMAN, T.H., RODERICK, H.R. Studies of cigarette smoke transfer using radioisotopically labelled tobacco constituents. Beitraege zur Tabakfomchung 7(3): 143153, November 1973. (16) DEBIAS, D.A., BANERJEE, CM., BIRKHEAD, NC., GREENE, C.H.. SCOTT, S.D., HARRER, W.V. Effects of carbon monoxide inhalation on ventricular fibrillation. Archives of Environmental Health 31: 42-46, January/February 1976. 14-82 (17') DEBIAS, D.A., BANERJEE, C.M., BIRKHEAD, N.C., HARRER, W.V., KAZAL, L.A. Carbon monoxide inhalation effects following myocardial infarction in monkeys. Archives of Environmental Health 21: 161-167, September 1973. (18) DEBIAS, D.A., BIRKHEAD, N.C., BANEBJEE, C.M., KAZAL, L.A., HOG BURN, RR., GREENE, C.H., HARRER, W.V., ROSENFELD, L.M., MEN- DUKE, H., WILLIAMS, N., FRIEDMAN, M.H.F. The effects of chronic exposure to carbon monoxide on the cardiovascular and hematologic systems in dogs with experimental myocardial infarction. Intemationales Archiv fuer Arbeitsmedixin 29: 253-Z67,1972 (19) FECHTER, L.D., ANNAU, Z. Toxicity of mild prenatal carbon monoxide exposure. Science 197: 680-682, August 12,1977. (20) FEYERABEND, C., LEVITT, T., RUSSELL, M.A.H. A rapid gas-liquid chromatographic estimation of nicotine in biological fluids. Journal of Pharmacy and Pharmacology 27: 434-436,1975. (21) FISHER, ER., ROTHSTEIN, R, WHOLEY, M.H., NELSON, R Influence of nicotine on experimental atherosclerosis and its determinants Archives of Pathology 96: 298-304, November 1973. (22) FRASCA, J.M., AUERBACH, O., PARKS, VR., JAMIESON, J.D. Electron microscopic observations on pulmonary fibrosis and emphysema in smoking dogs. Experimental and Molecular Pathology 15(l): 108-125, August 1971. (28) FREEMAN, G., DYER, RL., JUHOS, L.T., ST. JOHN, G.A., ANBAR, M. Identification of nitric oxide (NO) in human blood. Archives of Environmental Health 33: 1923, January/February 1978. (24) GUERIN, MR., MADDOX, W.L., STOKELY, JR. Tobacco smoke inhalation exposure: concepts and devices. In: Gori, G.B. (Editor). Proceedings of the Tobacco Smoke Inhalation Workshop. U.S. Department of Health, Education, and Welfare, Public Health Service, National Institutes of Health, DHEW Publication No. (NIH) 75996,1975, pp. 3144. (25) HANSSGN, E., SCHMITERLOW, C.G. Metabolism of nicotine in various tissues In: von Euler, U.S. (Editor). Tobacco Alkaloids and Related Com- pounds. Oxford, Pergamon Press, 1965, pp. 87-99. (26) HRUBES, V., BAETTIG, K. Effects of inhaled cigarette smoke on swimming endurance in the rat. Archives of Environmental Health 21: 2&24, July 1970. (27) ILEBEKK, A., LEKVEN, J. Cardiac effects of nicotine in dogs. Scandinavian Journal of Clinical and Laboratory Investigation 33: 153-1591974. (28) LANGLOSS, J.M., HOOVER, E.A., KAHN, D.E. Diffuse alveolar damage in cats induced by nitrogen dioxide or feline calicivirus. American Journal of Pathology 89(3): 637-644, December 1977. (29) MADDOX, W.L., DALBEY. W.E., GUERIN, MR. STOKELY, J.R, CREASIA, D.A., KENDRICK, J. A tobacco smoke inhalation exposure device for rodents. Archives of Environmental Health 33: 64-71, March/April 1978. (30) MCGILL, H.C., JR., ROGERS, W.R., WILBUR, RL., JOHNSON, D.E. Cigarette smoking baboon model: Demonstration of feasibility (40119). proceedings of the Society for Experimental Biology and Medicine 157: 67%676,1978. (Sf) MILLER, R.P., ROTENBERG, K.S., ADIR, J. Effect of dose on the pharmacoki- netics of intravenous nicotine in the rat. Drug Metabolism and Disposition 5(5): 436443,1977. (22) MORDELET-DAMBRINE, M., STUPFEL, M., DURIEZ, M. Comparison of tracheal pressure and circulatory modifications induced in guinea pigs and in rats by carbon monoxide inhalation. Comparative Biochemistry and Physiology 59A: 6568.1978. 14-83 (33) NETTESHEIM, P., GUERIN, M.R., KENDRICK, J., RUBIN, I., STOKELY, J., CREASIA, D., MADDOX, W., CATON, J.E. Control and maximization of tobacco smoke dose in chronic animal studies. In: Gori, G.B. (Editor). Proceedings of the Tobacco Smoke Inhalation Workshop. U.S. Department of Health, Education, and Welfare, Public Health Service, National Institutes of Health, DHEW Publication No. (NIH) `75996,1975, pp. 17-26. (34) NORMAN, V., KEITH, C. H. Nitrogen oxides in tobacco smoke. Nature 295(4974): 915916, February 27,1965. (35) PARK, S.S., KIKKAWA, Y., GOLDRING, I.P., DALY, M.M., ZELEFSKY, M., SHIM, C., SPIERER, M., MORITA, T. An animal model of cigarette smoking in beagle dogs. American Review of Respiratory Disease 115: 971-979, 1977. ($6) REECE, W.O., BALL, R.A. Inhaled cigarette smoke and treadmillexercised dogs. Archives of Environmental Health 24: 262270, April 1972. (99 RINK, R. D. The acute effects of nicotine, tobacco smoke and carbon monoxide on myocardial oxygen tension in the anaesthetised cat. British Journal of Pharmacology 62: 591-597,1978. (38) RYLANDER, R. Relative role of aerosol and volatile constituents of cigarette smoke as agents toxic to the respiratory tract. Toward a Less Harmful Cigarette. National Cancer Institute Monograph No. 28. U.S. Department of Health, Education, and Welfare, Public Health Service, National Institutes of Health, National Cancer Institute, 1968, pp. 221-229. (89) U.S. PUBLIC HEALTH SERVICE. The Health Consequences of Smoking. A Report of the Surgeon General: 1972. U.S. Department of Health, Education, and Welfare, Public Health Service, Health Services and Mental Health Administration, DHEW Publication No. (HSM) 727516,1972,158 pp. 14-84 Pharmacology of Cigarette Smoke For the habitual smoker, the smoking of a cigarette is a rewarding experience, evidenced by the consumption of over 606 billion cigarettes annually in the United States. It is a reward which is highly anticipated by smokers, one that seems to satisfy a smoker's physiological and psychological needs. Because of the myriad compounds present in cigarette smoke, it should be kept in mind that the pharmacological effects of smoking are not related solely to nicotine; rather, it is the combined effect of the whole smoke. Nevertheless, nicotine is generally accepted as the principal constituent responsible for cigarette smokers' pharmacologic response (6,20), and will be reviewed on this criterion. Nicotine is a powerful, quick-acting, ganglionic stimulant, eliciting its effects initially by depolarizing the ganglionic cells, stimulating both the sympathetic and parasympathetic ganglia (15). Nicotine Absorption Clearly, before any pharmacologic response can be elicited by nicotine from cigarette smoke, absorption must occur. The phenomenon of cigarette smoke absorption has been addressed by several investigators (2,4,&g, 16). Some absorption takes place in the oral cavity. Based on monitoring carotid blood levels and radiolabeled nicotine cigarettes, estimates from three studies (2,4, S) show that less than 30 percent of the inhaled dose is absorbed. Further, Artho and Grob (6) observed that there were striking differences in nicotine absorption that are largely determined by the pH of the total smoke. The p& values of nicotine are 6.16 and 10.96 (9). From these data, the portions of the diprotonated nicotine and monoprotonated nicotine as well as the free nicotine can be calculated for a given pH. Because cigarette smoke typically has a pH of 5-7, the diprotonated form need not be considered in this discussion. The percentage of nicotine present as the free base is 0.40 at pH 5.35, 1.7 at pH 6,15 at pH 7,64 at pH 8, and 85 at pH 8.5. The basic, lipid-soluble, uncharged nicotine is the form absorbed by the oral muscosa (8). A contributing factor to its absorption is that nicotine, as the free base, is volatile, which allows for rapid absorption from the gas phase. The relationship of the effects of pH are described in Figure 9 (9). Figure 10 (4) describes the oral absorption of nicotine from an identical dose of a buffered nicotine solution at pH 6,7, and 8. Nicotine which passes the oral cavity, as in cases of deep inhalation, is absorbed to a much greater extent than in the oral cavity. It is estimated that more than 90 percent of the inhaled nicotine is absorbed in the lungs (2, 6, 16). It should be noted also that retention of other cigarette smoke components by absorption is approximately 82 to 99 14-85 c p 7o E60 g50 : 40 2 30 2 m Es 20 g 10 B 0 8 1 2 3 4 5 6 7 6 9 10 11 12 OH . . FIGURE g--Degree of protonation of nicotine in relation to pH (pH = pKa log 1 - a/(r (Henderson/Hasselbach)). SOURCE: Aviado, D.M.. (7). a---- id-t6 . . .I... . . . . pH , - pH6 1 Time (h) FIGURE IO.-Carotid blood levels of nicotine in ng/ml, after the presence in the mouth for 10 minutes of buffered solutions of nicotine at pH 6, pH 7, and pH 8. The bars show standard error of the mean. SOURCE: Artbo. AA. (6). 14-86 percent, depending on the study. In any case, it is clear that the lung uptake of the nicotine in cigarette smoke is very efficient. Whether cigarette smoke or a nicotine aerosol is used seems to make little difference on nicotine absorption in the lung. Herxheimer (28) found that inhalation from smoke and inhalation from a nicotine aerosol in approximately equivalent amounts (about 100 pg every 30 seconds) produced similar increases in pulse rate and blood pressure in healthy volunteers. The equivalence is bnly approximate, however, because the nicotine delivered per puff increases as the cigarette is smoked. This increase could explain why, although similar, the peak effects occurred later-with cigarette smoking than with inhalation of the aerosol. Although pH of the smoke is a major factor in nicotine absorption, other factors such as tobacco smoke contact time with mucus membranes, pH of the mucus membrane, pH of body fluids, depth and degree of inhalation, degree of habituation of the smoker, nicotine and moisture content, and puff frequency must be considered (12,2O). Armitage, et al. (3) recently studied the effects of nicotine absorption in humans, comparing nicotine levels obtained in arterial blood. They found that arterial blood plasma concentrations of nicotine were comparable; however, the level rose more slowly in the smokers of small cigars. This may be due to a greater amount of the small cigar smoke being absorbed via the oral Cavity as compared-to cigarette -smoke, which is primarily absorbed via the lung. Alteration of Enzyme Systems The nature of tolerance to nicotine and tobacco smoking has received attention and a complex picture has emerged .(25). Studies with humans using high and low doses of nicotine presented apparently conflicting results regarding nicotine-cotinine metabolism. The authors suggested that acute high doses of nicotine produced inhibition of nicotine metabolism while lower daily doses on chronic exposure produced induction of the enzyme systems. These results are not uniformly accepted, however (51). Gorrod and Jenner (25) concluded that the effect of nicotine is complex, but that the data suggest the importance of dosage, length of administration, and stress-induced effects. They also stated that a component of cigarette smoke other than nicotine may be responsible for the changes in nicotine metabolism observed in humans. In any case, tobacco smoke is a known inhibitor of enzyme systems, including dehydrogenases and oxygenases, so that inhibition of nicotine met&o- lism or other metabolic products is a distinct possibility (273. Catecholamine Responses Since nicotine is a ganglionic stimulant on both the sympathetic and parasympathetic nervous systems, it is not surprising that investiga- 14-87 150 r MINUTES FIGURE Il.-Mean (-+ S.E.) plasma norepinephrine and epineph- rine concentrations in association with smoking (closed symbols) and sham smoking (open symbols). The arrows indicate the period of smoking (or sham smoking). SOURCE: Cutting, W.C. (1.5). tors have looked at catecholamines as possible indicators of the nicotine-induced effects. Moreover, the catecholamines are usually considered to be released in stress-related responses. The source of the catecholamines is reported to be in the myocardial chromaffin tissue and the adrenal gland (11, 29, 31), and therefore consistent with this hypothesis. Armitage (1) claims that the amount of nicotine inhaled during smoking is sufficient to cause release of catecholamines, but there is not uniform agreement on this subject (60, 63). Timing may be a critical factor in determining any catecholamine response because the response is likely to be transient. Cryer and coworkers (IS) have graphically shown the rapid response of nonepinephrine and epineph- rine as a consequence of cigarette smoking (see Figure 11). Naquira and coworkers (48) studied the chronic administration (14 days) of nicotine in rats. They observed increased tyrosine hydroxylase 14--88 and dopamine+hydroxylase in the hypothalamus and adrenal medul- la, but did not observe changes in tyrosine hydroxyiase in the striatum. The data suggest that chronic nicotine administration can produce similar long-term alterations in both catecholamine-forming enzymes in the hypothalamus and adrenal medulla. Catecholamines, released as a consequence of the nicotine-induced response, have been associated with or implicated in several biological responses. Cardiovascular-related diseases, bronchoconstriction and related pulmonary manifestations, fat metabolism, hyperglycemic effects, and the patellar reflex response have implicated catechol- amines as being either directly or indirectly involved in these biological endpoints. In the United States, more people die from coronary heart disease than from any other disease, and heart disease is the single most important cause of death among cigarette smokers(62). Epidemiologi- cal studies such as those reported by Mulcahy, et al. (4.5) who found a positive association between coronary heart disease mortality rate and the calculated per capita cigarette consumption in 21 countries, the Framingham study (19, 23, 33, 50), and reviews by Aronow (5) and Kannel (32) leave little doubt as to the consequences of cigarette smoking with respect to heart disease. Cardiovascular and Related Effects It is generally agreed that the acute cardiovascular effects of tobacco smoking can be attributed to the nicotine content of the cigarette and the amount absorbed (24, 20); similar effects have been observed by Irving and Yamamoto on administration of a comparable amount of nicotine by injection (31). The responses observed are those expected from stimulation of the sympathetic nervous system (15), including stimulation of the sympathetic ganglia, adrenal medulla, and the release of endogenous catecholamines (14). Responses are known to include increased heart rate and blood pressure (2, 28), cardiac output stroke volume, velocity of contraction, myocardial contractile force and oxygen consumption, and coronary blood flow and arrythmias (15,20). Activation of the chemoreceptors of the carotid and aortic bodies results in vasoconstriction, tachycardia, and elevated blood pressure. Nadeau and James (47) have shown that the cardiac/stimulating effect of nicotine can be attributed to vagal stimulation. The possible role of elevated serum corticoids, following smoking of high nicotine ciga- rettes, in sensitizing the myoeardium to the effects of the catechol- amine has been suggested (5, 29) as also possibly contributing to ventricular arrythmias and myocardial infarctions. Further research has been suggested to resolve this issue (5). Armitage and coworkers (3) have graphically described the dose- response effects of nicotine intravenous injection and cigarette 14-89 smoking as they affect blood pressure and heart rate. These results are described in Figure 12. Pulmonary Effects The respiratory effects of nicotine from smoke exposure are more difficult to quantify than cardiovascular effects because respiratory function may also be influenced by the solid particles or gases in cigarette smoke (i.e., CO and COe). For example, Reintjes and coworkers (50) were able to show that airway resistance values obtained immediately after smoking were elevated, but they did not identify the response as being caused by the nicotine in cigarette smoke. Aviado and coworkers (7) demonstrated that cigarette smoke causes acute bronchoconstriction by release of histamine and by stimulation of the parasympathetic nervous system in the lungs. Similar responses were shown to occur with arterial injections of nicotine. The effect is followed, however, by bronchodilation attributed to sympathetic stimulation. Fat Metabolism Changes in free fatty acids and mobilization of free fatty acids (FFA) have also been reviewed (40) as secondary effects of catecholamine stimulation. Kershbaum and coworkers (35) were led to the conclusion that nicotine had no direct lipolytic effect on cat or dog adipose fat tissue. Their findings lent support to the concept that mobilization of FFA by nicotine and cigarette smoke was a result of their stimulation of sympathetic nervous system activity and catecholamine secretion. In a related study (36) comparing 4 mg of nicotine in intravenously- and intratracheally-administered cigarette smoke, the authors suggested that tobacco smoking and nicotine caused an increased utilization of FFA in addition to their known effect of FFA mobilization. It was suggested that the greater FFA utilization was caused by increased cardiac output due to nicotine. The authors further suggested that nicotine changes the ratio of FFA incorporated into neutral lipid and phospholipids. Hyperglycemic Effects Another secondary response to the catecholamines present in the blood stream is believed to be a hyperglycemic condition as described in a recent review (40). Such a response would be consistent with a stress- related situation requiring an energy source for quick response. Milton (44) has suggested that in cats the hyperglycemic mobilizing action of smoking doses of nicotine is due entirely to stimulation of the adrenal gland, while the hyperglycemic effect at high doses is presumably due to stimulation of ganglia throughout the body resulting in the release of more epinephrine. 14-w , . I I :: :: :: :: n i-4 1 1 FIGURE 12.-Arterial blood levels of W-nicotine (0) and W- cotinine (0), heart rate (a), and blood pressure (m) during and after smoking a cigarette labeled with W-nicotine (a), and during and after intravenous administration of 1 mg W-nicotine in 10 divided doses W. SOURCE: Bed&t, AH. (8). 14---91 Other Central Nervous System Effects It has recently been reported that nicotine also causes a diminution in the monosynaptic patellar reflex (18). This reduction in the patellar reflex was not seen after smoking nontobacco cigarettes. The effect thus appears to be closely related to nicotine. This was later confirmed by Domino and Baumgarten (18) after studying the response to an inhaled nicotine aerosol. Metabolism of Nicotine The metabolism of nicotine has been examined and reviewed by several investigators (25, 27, 61). The major part of the absorbed nicotine is metabolized rapidly in the body, and studies have established the liver as the major organ of detoxication. McKennis, et al. (20~2od) have demonstrated that cotinine is the major metabolite of nicotine in human and animal urine. Other detected metabolites are summarized in Figure 13. Hansson and Schmiterlow (2?`), using radiolabeled nicotine, were able to detect radiolabeled products only in cotinine and COP. In studying tissue slices, they determined that nicotine is metabolized in the kidney and lung as well as in the liver, but not in the brain, diaphragm, spleen, stoma;h, small intestine, or adrenal glands. Armitage (2), in comparing the effects of injected nicotine and innaled cigarette smoke, found that the half-life of nicotine in the arterial blood of smokers ranged from 24 to 84 minutes, with a mean value of 40 minutes when only the inhalation experiments were taken inlx, account. In examining the relationship between intravenous injections of nicotine and subsequent metabolism, Miller, et al. (.@) found nicotine had a tVz of 55 to 64 minutes, with peak levels in the range of 297 ng/ml of plasma, While there was no effect of the administered dose on disappearance rate, there was a suggestion that the dose affected the distribution of nicotine. This would appear reasonable, in view of the known vasoconstrictive properties mentioned earlier, and could explain some of the conflicts in characterizing nicotine's pharmacologic properties. Tsujimoto and coworkers (59) studied the tissue distribution of nicotine in dogs and rhesus monkeys. Five minutes after injection the adrenal medulla and cerebral cortex contained the highest concentra- tion of nicotine. Other tissues containing significant quantities of nicotine included the spleen, adrenal cortex, kidney, and pancreas. The effect of urinary pH on the excretion of nicotine and its metabolites has been studied by Beckett, et al. (8), Corrod and Jenner (25), and Feyerabend and Russell (21). They determined that the amount of unchanged nicotine excreted in the urine after oral administration was dependent on pH, while cotinine was dependent on FIGURE It.-Nicotine metabolism. SOURCE: Hanaaon. E. ($7). urinary pH and flow rate. Specifically, the more acidic the urine, the larger the amount of unchanged nicotine. Similar results were obtained by Schachter and coworkers in reviewing the effect of urine pH as a result of stress-related factors (55,56). Metabolic Products in Test Animals from Nicotine in Cigarette Smoke Investigations of nicotine metabolites from cigarette smoke, using various animal systems including man (25, 27), has led to the identification of several metabolites. An extensive investigation of 14-93 nicotine metabolites has been performed by Gorrod and Jenner (25). In the mouse, the metabolic products identified were cotinine, hydroxyco- tinine, y-(3-pyridyl)-y-oxo-N-methylbutyramide, CO2 and two unidenti- fied products separated by chromatography (27'). The primary metabo- lites identified by Gorrod and Jenner include nicotine-l'-N-oxide, 5'- hydroxycotinine, cotinine, nornicotine, and isomethylnicotinium ion (25). Other metabolic products (Figure 13) are considered to be derived from those mentioned above. Only cotinine and nornicotine have been examined for their pharmacologic activity in any detail; these will be discussed below. The complex mechanism by which cotinine, the major metabolite, is formed involves at least two enzyme systems. Both 5' hydroxynicotine and nicotine AN*`(5') iminium ion have been implicated as intermedi- ates (30, 46). Cotinine is further metabolized by pyrrolidone ring hydroxylation; all other metabolites of nicotine are thought to arise by cleavage of the phrrolidone ring of cotinine. Related Alkaloids and Their Metabolites in Cigarette Smoke It is difficult to generalize regarding the amount of various alkaloids other than nicotine in cigarettes because of differences in the alkaloid content and composition of the various tobacco strains employed in cigarette manufacture. However, nicotine is usually considered to account for about 95 percent of the alkaloids in tobacco. The remainder consists of varying proportions of nornicotine, anabasine, myosmine, anatabine, nicotyrine, and other alkaloids described in Figure 14 (38). As stated above, nicotine is considered to be primarily responsible for eliciting the pharmacologic effects in cigarette smoke. Nevertheless, Using a battery of tests, Clark and coworkers (13) compared the pharmacological activity of a number of the minor alkaloids known or suspected to occur in tobacco smoke. Their results are summarized in Table 21. It should be noted, however, that only nicotine was optically pure. Others either were prepared synthetically, yielding racemic products, or were isolated under conditions resulting in optically inactive forms; therefore, the pharmacological responses reported may be less than would have been obtained had the optically active compounds (where appropriate) been tested. The LDSO values of several alkaloids in various species have been tabulated (573. Extrapolation of these data to other species and to the effects of multiple dosing, however, may not be useful because of variation in metabolic pathways among species. Pharmacodynamics Until recently, relatively little attention was devoted to the pharmaco- dynamics of cigarette smoke. However, with increasing interest in smoking cessation techniques (42), tobacco industry emphasis on 14-94 R = H. Nomlcobne R = CH~, Ncobne R = H. Anabasme R = H. Anawme R = CH~ Khlelhy~ R = c"g N-MM?+ mabasme alahblae 2.3-DipyMyl FIGURE Il.-Structural formulas of some tobacco alkaloids. SOURCE: k8011. P.S. (40). 14-95 TABLE 21.--Relative molar potency of nicotine and other cigarette smoke alkaloids Alkaloid Nicotine 100 Nornicotine 4.5 M&nicotine 4 Anabasine 17.5 Myosmine 0.2 Nicotyrine 0.3 2:%Dipyridyl 0.2 Dibydrometanicotine <0.025 N-Metbylanabasine <0.023 Cotinine