Regulation of Vascular Tone

to฀improve฀endothelial฀function฀in฀chronic฀cigarette฀smokers,฀as฀demonstrated฀by฀an฀increased฀ forearm฀blood฀low฀response฀to฀acetylcholine,฀whereas฀there฀was฀no฀effect฀on฀the฀response฀to฀ sodium฀nitroprusside฀ [97] .฀Bradykinin-mediated฀NO฀release฀induced฀by฀lisinopril฀has฀been฀ suggested฀as฀the฀possible฀mechanism฀responsible฀ [96] .฀In฀contrast฀to฀smoking,฀nicotine฀e.g.฀ when฀administered฀as฀a฀patch฀does฀not฀reduce฀the฀surface฀area฀of฀coronary฀segments฀and฀also฀ does฀not฀additively฀enhance฀the฀vasoconstrictor฀effect฀of฀sympathetic฀stimulation฀produced฀ by฀the฀cold฀pressor฀test฀ [98] .฀Differences฀between฀cigarette฀smoke฀and฀nicotine฀were฀also฀seen฀ in฀changes฀of฀the฀low-mediated฀dilatation฀FMD฀which฀declined฀in฀16฀healthy฀smokers:฀this฀ variable฀declined฀to฀a฀greater฀extent฀after฀smoking฀one฀cigarette฀1฀mg฀nicotine฀than฀after฀ administration฀of฀nasal฀spray฀1฀mg฀nicotine฀means:฀−3.6฀vs.฀−5.1;฀smoke฀vs.฀nicotine.฀ Nitroglycerine-induced฀dilatation฀remained฀similar฀under฀both฀experimental฀conditions฀ [99] .฀ Irrespective฀of฀differences฀in฀nicotine฀kinetics฀after฀the฀two฀methods฀of฀administration,฀the฀ mechanism฀of฀action฀of฀nicotine฀on฀the฀endothelium฀remains฀unclear. In฀terms฀of฀nitric฀oxide฀NO฀release,฀endothelial฀NO฀synthase฀NOS฀gene฀polymor- phism฀ab฀polymorphism฀plays฀a฀decisive฀role฀in฀the฀occurrence฀of฀acute฀myocardial฀ infarction.฀This฀risk฀is฀increased฀particularly฀in฀younger฀smokers฀aged฀฀51฀years฀with฀ aa฀polymorphism,฀irrespective฀of฀the฀additional฀presence฀of฀diabetes฀mellitus฀or฀hyper- tension฀ [100] . The฀vasoconstrictor฀effect฀on฀coronary฀vessels฀may฀be฀caused฀by฀reduced฀prostacyclin฀ PGI 2 ฀levels฀in฀the฀coronary฀endothelial฀cells.฀In฀comparison฀with฀non-smokers,฀smokers฀ have฀reduced฀blood฀levels฀of฀PGI 2 ฀and฀increased฀blood฀levels฀of฀11-dehydro-TXB 2 ฀ [101,฀ 102] .฀Nevertheless,฀the฀reactions฀produced฀by฀cigarette฀smoking฀in฀terms฀of฀adrenaline,฀ noradrenaline฀and฀dopamine฀release฀are฀different฀from฀those฀produced฀by฀nicotine฀admin- istration,฀as฀shown฀by฀the฀data฀presented฀in฀Table฀ 6.1 .฀Catecholamine฀release฀due฀to฀nico- tine฀administration฀is฀quantitatively฀smaller฀than฀that฀due฀to฀cigarette฀smoke฀ [95,฀103] . During฀cigarette฀smoking,฀nicotine฀is฀absorbed฀very฀rapidly,฀leading฀to฀varying฀degrees฀ of฀adrenaline-฀and฀noradrenaline-induced฀vasoconstriction฀via฀a 1 -adreno-ceptor฀stimula- tion.฀Occasional฀smokers฀compensate฀for฀this฀vasoconstrictor฀effect฀by฀releasing฀NO฀and฀ prostacyclin฀from฀endothelium,฀whereas฀in฀heavy฀smokers฀this฀mechanism฀no฀longer฀oper- ates.฀In฀this฀context฀it฀should฀be฀pointed฀out฀that฀vascular฀tone฀is฀regulated฀by฀two฀vasoac- tive฀substances฀with฀opposing฀effects:฀NO · ฀and฀O 2 –· .฀NO฀has฀a฀pivotal฀role฀here,฀particularly฀ Noradrenaline฀ [pgml] Adrenaline฀[pgml] Control฀patients 227฀23 44฀4 Smokers 324฀39 113฀27 Plasma฀nicotine฀ AUC฀ [ngml.h] Noradrenaline฀ [µgg฀ creatinine] Adrenaline฀[µgg฀ creatinine] Dopamine฀ [µgg฀ creatinine] Cigarette฀smoking 451฀±฀62 176฀±฀23 28฀±฀3 1,099฀±฀86 Nicotine฀patch 356฀±฀30 166฀±฀25 21฀±฀3 1,051฀±฀87 Placebo฀patch – 172฀±฀20 22฀±฀2 950฀±฀65 p-value n.s 0.06 0.05 0.05 Table 6.1 ฀฀฀Catecholamine฀ release฀ associated฀ with฀ cigarette฀ smoking฀ [38] ฀ mean,฀ mean฀ standard฀ error฀ and฀ urinary฀ catecholamine฀ excretion฀ in฀ smokers฀ and฀ following฀ nicotine฀ administration฀ patch฀ [171] since฀post-occlusive฀vasodilatation฀in฀the฀forearm,฀for฀example฀is฀associated฀with฀NO฀ production฀and฀release฀from฀endothelium.฀NO฀is฀formed฀from฀ l -arginine฀by฀NOS,฀which฀ is฀ dependent฀ on฀ NADPH,฀ lavin฀ adenine฀ nucleotides฀ and฀ tetrahydrobiopterin฀ THB.฀ Atherogenic฀activity฀has฀been฀attributed฀to฀the฀toxic฀substance฀ONOO – ,฀in฀conjunction฀ with฀activation฀of฀the฀renin-angiotensin฀system฀ [104] .฀NO฀is฀able฀to฀form฀free฀radicals,฀and฀ to฀activate฀guanylate฀cyclase฀in฀endothelial฀cells฀and฀platelets฀Fig.฀ 6.4 . Acute฀cigarette฀smoking฀leads฀to฀temporary฀endothelial฀dysfunction,฀which฀is฀an฀early฀ event฀in฀atherogenesis.฀Suficient฀data฀concerning฀the฀effect฀of฀cigarettes฀with฀low฀tar฀and฀ nicotine฀yield฀are฀lacking.฀Therefore,฀Papamichael฀et฀al.฀studied฀seventeen฀healthy฀indi- viduals฀nine฀women,฀eight฀men,฀aged฀27.8฀±฀3.6฀years฀who฀were฀subjected฀to฀evaluation฀ of฀endothelial฀function฀by฀means฀of฀endothelium-dependent,฀FMD฀of฀the฀brachial฀artery,฀ before,฀immediately฀after฀and฀30,฀60฀and฀90฀min฀after฀smoking฀a฀regular฀cigarette฀nicotine฀ 0.9฀mg,฀tar฀12฀mg฀or฀the฀corresponding฀“light”฀cigarette฀nicotine฀0.6฀mg,฀tar฀8฀mg฀ [105] .฀ The฀following฀day,฀measurements฀were฀repeated฀after฀smoking฀the฀opposite฀kind฀of฀ciga- rette.฀ Baseline฀ FMD฀ was฀ 6.1฀ ±฀ 1.6฀ and฀ 7.2฀ ±฀ 2.0฀ in฀ the฀ light฀ and฀ regular฀ cigarette฀ groups,฀respectively฀p฀=฀NS.฀The฀overall฀effect฀of฀the฀regular฀cigarette฀over฀time฀on฀FMD฀ compared฀with฀the฀light฀cigarette฀was฀signiicantly฀different฀F฀=฀3.039,฀p฀=฀0.023.฀FMD฀ was฀signiicantly฀depressed฀after฀smoking฀both฀types฀light:฀F฀=฀8.192,฀p฀฀0.001;฀regular:฀ F฀=฀16.698,฀p฀฀0.001.฀Immediately฀after฀smoking,฀FMD฀declined฀in฀both฀groups฀light:฀3.0฀ ±฀2.4฀and฀regular:฀1.6฀±฀3.2,฀p฀฀0.001฀and฀p฀฀0.001,฀respectively,฀and฀it฀remained฀ signiicantly฀depressed฀in฀the฀regular฀cigarette฀group฀at฀30฀min฀0.75฀±฀1.5,฀p฀฀0.001฀and฀ 60฀min฀3.5฀±฀3.1,฀p฀=฀0.024,฀while฀in฀the฀light฀cigarette฀group฀FMD฀differences฀were฀ Smoking lipid radical induced lipid peroxidation lipid peroxides THB synthesis THB synthesis I-arginine I-arginine endothelium-dependent relaxation is impaired Fe 2+ endothelium smooth muscle Increased blood flow Ca 2 NOS NOS NO NO + + + smooth muscle relaxation guanylate cyclase Fig. 6.4 ฀฀฀Harmful฀effects฀of฀smoking฀on฀vascular฀relaxation.฀A฀rise฀in฀Ca 2+ ฀causes฀an฀increase฀in฀NO฀ synthesis฀ from฀ l -arginine฀ by฀ NOS.฀ Tetrahydrobiopterin฀ THB฀ is฀ an฀ important฀ co-factor.฀ NO฀ penetrates฀the฀vascular฀cell฀and฀stimulates฀guanylate฀cyclase;฀this฀in฀turn฀forms฀cGMP฀which฀has฀ a฀vasodilator฀action.฀Smoking฀limits฀the฀synthesis฀of฀cGMP.฀In฀addition,฀the฀radicals฀formed฀in฀the฀ blood฀promote฀oxo-LDL฀formation.฀A฀fall฀in฀THB฀also฀reduces฀NO฀synthesis฀ [209] abolished฀at฀30,฀60฀and฀90฀min฀after฀smoking.฀The฀authors฀concluded฀that฀acute฀smoking฀of฀ both฀regular฀and฀light฀cigarettes฀leads฀to฀temporary฀vasomotor฀dysfunction;฀its฀duration฀is฀ shorter฀after฀smoking฀a฀“light”฀cigarette฀ [105] . Vasodilatation฀and฀inhibition฀of฀platelet฀aggregation฀is฀achieved฀as฀a฀result฀of฀cGMP฀ release.฀NO฀is฀therefore฀of฀major฀pathogenetic฀importance฀in฀that฀it฀prevents฀platelet฀aggre- gation,฀monocyte฀adhesion฀and฀vascular฀smooth฀muscle฀cell฀proliferation.฀By฀reducing฀NO฀ formation,฀ smoking฀ counteracts฀ these฀ preventive฀ processes฀ [106] .฀ Where฀ dysfunctional฀ NOS฀III฀activity฀is฀associated฀with฀inhibition฀of฀NO฀production,฀supplementary฀administra- tion฀ of฀ THB฀ improves฀ endothelium-dependent฀ vasodilatation฀ in฀ chronic฀ smokers฀ [107] .฀ Glyceryl฀trinitrate฀or฀sodium฀nitroprusside฀inluence฀these฀processes฀because฀they฀have฀a฀ vasodilator฀action฀in฀response฀to฀NO฀production.฀The฀interplay฀of฀LDL฀oxidation฀and฀NOS฀ dysfunction฀is฀supported฀by฀in-vitro฀experiments฀in฀saphenous฀vein฀rings฀and฀platelets฀ [108,฀ 109] ,฀showing฀that฀impaired฀endothelium-dependent฀relaxation฀is฀attributable฀to฀inadequate฀ THB฀synthesis฀resulting฀from฀the฀harmful฀effects฀of฀cigarette฀smoke฀constituents฀Fig.฀ 6.5 ฀ [108,฀110] .฀In฀hypercholesterolaemia฀the฀adverse฀effect฀on฀vascular฀function฀results฀from฀ the฀oxidation฀of฀LDL฀to฀oxo-LDL฀ [111] .฀As฀an฀antioxidant,฀ascorbic฀acid฀is฀reported฀to฀ improve฀smoking-induced฀vascular฀responses฀ [112] .฀Smoking-related฀endothelial฀damage฀ Smoking free radicals shear stress chemoattractants developing plaque containing monocytes macrophages and smooth muscle cells NO synthesis leucocyte adhesion molecules monocyte activation injured endothelium oxo- oxo- cytokines to recruit smooth muscle cells monocyte adhesion LDL LDL Fig. 6.5 ฀฀฀Smoking฀stimulates฀monocyte฀adhesion,฀migration฀and฀activation.฀Increased฀shear฀forces฀ alter฀the฀endothelial฀surface฀and฀increase฀the฀production฀of฀the฀adhesion฀molecules฀ICAM-1฀and฀ VCAM-1฀on฀vascular฀endothelium.฀In฀addition,฀chemical฀adhesives฀are฀released฀from฀monocytes,฀ and฀ the฀ reduction฀ in฀ NO฀ synthesis฀ increases฀ monocyte฀ adhesion฀ to฀ the฀ endothelial฀ cells.฀ The฀ endothelium฀becomes฀porous,฀with฀the฀result฀that฀oxo-LDL฀molecules฀are฀able฀to฀pass฀through.฀ These฀in฀turn฀activate฀monocytesmacrophages฀which฀release฀cytokines฀and฀growth฀factors฀–฀a฀ starting฀point฀for฀atherosclerotic฀changes฀in฀the฀vessel฀ [209] is฀partially฀reversible฀if฀smoking฀cessation฀is฀maintained฀for฀at฀least฀12฀months฀ [113,฀114] .฀ Disturbed฀prostacyclin฀synthesis฀is฀associated฀with฀the฀increased฀production฀of฀vasocon- strictor฀฀thromboxanes฀ [115] .

6.2.2 Changes in Endothelial Function and Microcirculation

The฀basis฀for฀the฀evolution฀of฀arteriosclerosis฀with฀subsequent฀cardiac฀events฀is฀formed฀by฀ smoking-induced฀changes฀in฀coronary฀vascular฀tone,฀increased฀platelet฀aggregation฀and฀ altered฀endothelial฀integrity,฀even฀in฀younger฀adults฀ [102,฀113] .฀Cigarette฀smoking฀pro- duces฀endothelial฀changes฀with฀detectable฀ultrastructural฀damage฀to฀the฀aorta฀and฀pulmo- nary฀vessels฀ [116–118] .฀The฀tobacco฀constituent฀NNK฀see฀Table฀ 3.6 ,฀Box฀3.1฀in฀ Chap.฀3 ฀ causes฀considerable฀endothelial฀damage.฀Its฀binding฀to฀b 1 -฀and฀b 2 -adrenoceptors฀is฀fol- lowed฀by฀activation฀of฀arachidonic฀acid,฀associated฀with฀endothelial฀damage฀and฀apoptosis฀ of฀ endothelial฀ cells.฀ These฀ effects฀ of฀ NNK฀ can฀ be฀ prevented฀ by฀ b-receptor฀ blockers฀ atenolol฀ [119] . Bernhard฀et฀al.฀demonstrated฀in฀2003฀that฀tobacco฀smoke฀dramatically฀changes฀vascular฀ endothelial฀cell฀and฀tissue฀morphology,฀leading฀to฀a฀loss฀of฀endothelial฀barrier฀function฀within฀ minutes.฀ In฀ these฀ experiments฀ long-term฀ exposure฀ of฀ endothelial฀ cells฀ to฀ tobacco฀ smoke฀ extracts฀induced฀necrosis฀that฀may฀trigger฀a฀pro-inlammatory฀status฀of฀the฀vessel฀wall฀ [120] .฀ Pre-incubation฀of฀the฀extracts฀without฀cells฀for฀6฀h฀at฀37°C฀led฀to฀a฀complete฀loss฀of฀activity.฀ Furthermore,฀the฀endothelium฀could฀be฀rescued฀by฀changing฀to฀fresh฀medium฀even฀at฀times฀ when฀the฀extracts฀had฀lost฀their฀activity.฀It฀was฀also฀shown฀that฀N-acetyl฀cysteine฀and฀statins฀ inhibit฀the฀adverse฀tobacco฀smoke฀effects฀ [120] . The฀regulation฀of฀vascular฀tone฀is฀disturbed฀when฀NO฀production฀is฀diminished.฀Based฀on฀ the฀damage฀to฀endothelial฀function฀outlined฀above,฀short฀periods฀of฀smoking฀potentiate฀the฀ vasoconstrictor฀ effect฀ of฀ endothelin-1฀ [121] .฀ It฀ has฀ long฀ been฀ known฀ that฀ endothelium- dependent฀coronary฀dilatation฀is฀disturbed฀in฀the฀presence฀of฀hypercholesterolaemia,฀the฀ premature฀ onset฀ of฀ arteriosclerosis฀ andor฀ hypertension฀ [122–124] .฀ In฀ addition,฀ habitual฀ smoking฀diminishes฀the฀vasodilator฀reserve฀of฀the฀tiniest฀vessels฀and฀thus฀encourages฀the฀ harmful฀hypoxic฀effects฀which฀are฀detectable฀in฀habitual฀smokers฀long฀before฀the฀appearance฀ of฀recognisable฀cardiovascular฀disease฀ [125,฀126] .฀Bradykinin-induced฀venous฀dilatation฀in฀ the฀dorsal฀veins฀of฀the฀hand฀is฀suppressed฀both฀in฀non-smokers฀and฀in฀smokers฀by฀transder- mal฀administration฀of฀nicotine,฀with฀the฀result฀that฀a฀pivotal฀role฀in฀endothelial฀dysfunction฀ must฀be฀conceded฀for฀the฀alkaloid฀ [127] .฀These฀studies฀have฀also฀shown฀a฀slight฀rise฀in฀blood฀ pressure฀in฀response฀to฀nicotine. Alongside฀endothelial฀damage,฀the฀low฀properties฀of฀the฀blood฀and฀blood฀coagulation฀ processes฀are฀also฀inluenced฀by฀cigarette฀smoking฀but฀not฀by฀nicotine฀Table฀ 6.2 .฀It฀is฀ generally฀accepted฀that฀plasma฀ibrinogen฀levels฀are฀increased฀in฀smokers,฀due฀to฀reduced฀ plasminogen฀activity฀in฀the฀blood฀ [128,฀129] ,฀and฀that฀increasing฀age฀leads฀to฀a฀further฀rise฀ in฀ibrinogen.฀As฀a฀result,฀the฀luidity฀of฀the฀blood฀is฀lowered฀and฀the฀viscosity฀of฀whole฀ blood฀and฀plasma฀is฀increased฀ [38,฀71,฀128,฀130] .฀The฀haemorheological฀properties฀of฀the฀ blood฀are฀further฀exacerbated฀by฀the฀increase฀in฀haematocrit฀ [130,฀131] ฀–฀evidently฀in฀ compensation฀for฀the฀transformation฀of฀up฀to฀15฀of฀haemoglobin฀into฀CO-haemoglobin฀ –฀and฀by฀the฀progressive฀decline฀in฀red฀cell฀deformability฀ [132,฀133] .฀The฀supply฀of฀O 2 ฀to฀ the฀tissues฀is฀thus฀also฀reduced.฀In฀addition,฀the฀following฀variables฀are฀elevated฀in฀smok- ers:฀leucocyte฀count฀ [134–136] ,฀CO-induced฀platelet฀aggregability฀ [41] ,฀and฀factor฀XIII฀ and฀von฀Willebrand฀factor฀activity฀ [136–138] .฀All฀these฀smoking-induced฀reactions฀tend฀to฀ normalise฀following฀smoking฀cessation฀andor฀nicotine฀substitution฀Table฀ 6.2 . Previous฀thinking฀concerning฀the฀important฀vasoconstrictor฀effect฀of฀nicotine฀in฀terms฀ of฀the฀evolution฀of฀vascular฀disease฀should฀be฀revised฀to฀take฀account฀of฀the฀very฀much฀ greater฀part฀played฀by฀CO฀and฀CO-haemoglobin฀and฀by฀glycoproteins฀in฀bringing฀about฀ changes฀in฀the฀vessels฀and฀the฀microcirculation฀Fig.฀ 6.1 ,฀Table฀ 6.2 ฀ [8] . Based฀on฀experimental฀animal฀work,฀it฀has฀been฀reported฀that฀nicotine฀stimulates฀new฀ blood฀vessel฀formation฀angiogenesis,฀and฀this฀is฀associated฀with฀endothelial฀proliferation฀ [139] .฀Overall,฀this฀study฀attributes฀tumorigenic฀activity฀to฀nicotine฀ [139] . Further฀research฀is฀required฀to฀conirm฀whether฀these฀results฀can฀be฀transposed฀to฀the฀ situation฀in฀man.฀To฀date,฀at฀least,฀there฀is฀no฀evidence฀to฀show฀that฀nicotine฀displays฀such฀ properties฀in฀humans.

6.2.3 Microcirculation and O

2 Supply Smoking-induced฀damage฀to฀the฀microcirculation,฀including฀the฀skin฀and฀O 2 ฀supply,฀has฀been฀ studied฀in฀humans฀and฀in฀experimental฀animals฀ [140–143] .฀In฀particular,฀dramatic฀reactions฀ have฀ been฀ demonstrated฀ in฀ smokers฀ undergoing฀ revascularisation฀ procedures฀ [144,฀ 145] .฀ Likewise,฀skin฀necroses฀have฀been฀described฀in฀smokers฀following฀cosmetic฀facial฀surgery฀ [141,฀146,฀147] .฀These฀harmful฀effects฀were฀elicited฀by฀the฀toxic฀constituents฀of฀cigarette฀ smoke฀and฀by฀CO,฀and฀to฀a฀very฀much฀smaller฀extent฀by฀nicotine฀ [9] .฀In฀smokers,฀skin฀laps฀ also฀show฀delayed฀healing฀or฀fail฀to฀survive฀at฀all฀see฀ Chap.฀7.8 ฀ [144,฀148,฀149] . Variables Smoking Nicotine Reference฀nos Plasma฀ibrinogen฀concentration Ý Û [71,฀128–130,฀136,฀137,฀ 157,฀203–205] Platelet฀aggregation฀CO-induced Ý Û [41] Haematocrit Ý Û [71,฀130,฀131] Leucocyte฀count Ý Û [135–137] von฀Willebrand฀factor Ý Û [136,฀137] Factor฀XIIa Ý Û [141] Plasminogen ß Û [128,฀129] Vascular฀permeability฀for฀ibrinogen Ý Û [206–208] Red฀cell฀deformability ß Û [132,฀133,฀173] Viscosity฀plasma,฀blood Ý Û [71,฀128,฀130,฀131] CO-haemoglobin Ý Û [95] Catecholamines฀in฀blood฀and฀urine Ý Ý ,฀Û [179,฀195] Table 6.2 ฀฀฀Differences฀between฀cigarette฀smoking฀and฀nicotine฀administration฀on฀haemorheological฀ variables฀ [8] Results฀from฀clinical฀studies.฀Ý:฀elevated,฀ß:฀low฀or฀reduced,฀Û:฀unchanged฀or฀normal