Effects of smoking and nicotine on human prostacyclin and thromboxane production in vivo and in vitro

The role of endothelial cell adhesion molecules in the development of atherosclerosis

The vascular endothelium serves as a dynamic interface between circulating blood elements and the interstitial tissues. As such, it communicates to cells within the vessel wall as well as to the surrounding tissue, sensing its environment and responding accordingly. The vasculature must maintain a delicate balance when initiating a functional response by producing both proinflammatory and antiinflammatory mediators, vasoconstrictors and vasodilators, growth stimulators and inhibitors, and prothrombogenic and antithrombogenic factors. Any response to injurious agents could lead to pathology. Confounding this complex interplay is the fact that the very response to injury that may have developed to undo the damage may itself be even more deleterious. One response to injury by the endothelium is the new or increased expression of surface receptors for immune elements. In atherosclerosis, the adhesion of monocytes (and T cells) to the endothelium is a key event triggered by some form of insult. Subsequent events include monocytic infiltration of the vessel wall, alterations in lipid metabolism, and the activation of these cells into foam cells. The presence of large numbers of foam cells in the intima may produce a high concentration of cytokines and growth factors within a localized area, extracellular matrix perturbations, smooth muscle cell proliferation, and ultimately platelet aggregation at the site of stenosis. Endothelial cells themselves will not only elaborate factors after the initial injury to the vessel wall but also in response to the factors produced by foam cells within the plaque. These endothelial cell factors include MCP-1, a chemoattractant for monocytes (179,180), IL-1 (63,64), IL-6 (interleukin-6) (65-67), IL-8 (interleukin 8) (181), and PDGF, a potent smooth muscle mitogen (4,72) (Fig. 3). Endothelial cells will propagate an inflammatory response long after the initial insult to the arterial vessel. A chronic cycle of endothelial cell activation and leukocyte infiltration is constitutively activated. Thus, all of the cellular elements of the vessel wall, as well as the atherosclerotic plaque itself, elaborate cytokines and growth factors that amplify and propagate the pathological process.

Arterial stiffening and systemic endothelial activation induced by smoking: The role of COX-1 and COX-2

BACKGROUND

Arterial stiffness is an established predictor of cardiovascular risk. We explored the effects of acute smoking on arterial stiffness, systemic inflammation and endothelial activation in chronic smokers and the contribution of cyclooxygenases-1 and 2 (COX-1 and COX-2).

METHODS AND RESULTS

In a randomized, double-blind, cross-over study, we investigated in 28 young smokers the vascular and systemic effects of smoking one cigarette, 3h after receiving 1000 mg of aspirin (a non-selective COX-1 and COX-2 inhibitor) or placebo (aspirin substudy), or 200 mg of celecoxib (a selective COX-2 inhibitor) or placebo (celecoxib substudy). Smoking increased carotid-femoral pulse wave velocity (PWV, a marker of aortic stiffness), indicating an adverse effect on arterial elastic properties. Similarly, circulating levels of asymmetric dimethylarginine (ADMA) were increased after smoking. Aspirin fully prevented the smoking-induced increase of PWV after smoking. In contrast, celecoxib only partially prevented the smoking-induced increase of PWV. Both aspirin and celecoxib prevented to a similar extent the increase of ADMA levels after smoking.

CONCLUSIONS

Smoking one cigarette is associated with a deterioration of arterial stiffness and with systemic endothelial activation in chronic smokers. Both COX-1 and COX-2, but primarily COX-1, mediate these unfavorable effects of smoking.

Effects of nicotine, its metabolites and tobacco extracts on human platelet function in vitro

Cigarette smoking is a leading cause of cardiovascular disease. The cardiovascular effects of smoking are probably multifactorial, including effects on platelets. Previous reports investigating the effects of nicotine and tobacco on platelet function are inconsistent. The present study investigated in vitro effects of nicotine, its major metabolites, tobacco extracts and extract of tobacco-free snuff on human platelets. None of the metabolites cotinine, cotinine-N-oxide, nicotine-1'-N-oxide or trans-3'-hydroxycotinine (0.1-10 μM) affected platelet aggregation or P-selectin expression. Nicotine (10 μM) weakly increased platelet aggregation, whereas trans-3'-hydroxycotinine (0.1 μM) and nicotine-1'-N-oxide (1-10 μM) weakly inhibited adhesion to fibrinogen. To elucidate the influence of other tobacco compounds, we investigated the impact of moist tobacco and smoke extracts on platelet function. Filtered extracts of oral snuff, cigarette smoke and tobacco free snuff inhibited platelet adhesion concentration-dependently. The inhibitory effects of tobacco extracts on platelet adhesion were independent of nicotine content and the nitric-oxide-pathway and not mediated through a platelet-nicotine-receptor. Taken together, tobacco extracts inhibit platelet activation during short-term in vitro challenge. As only limited effects of nicotine and nicotine metabolites were seen, the tobacco-induced platelet inhibition are likely induced by other compounds present in tobacco and tobacco free snuff.

Cyclooxygenase-1 mediated platelet reactivity in young male smokers

BACKGROUND

The purpose of this study is to investigate the acute and chronic effects of cigarette smoking on cyclooxygenase- 1(COX-1)-mediated platelet reactivity among cigarette smokers.

METHODS

The levels of collagen-induced platelet aggregation, platelet COX-1 activity, and expressions were compared between smokers and age-matched nonsmokers. In smokers, the acute effects of cigarette smoking were assessed by repeating these measurements an hour after smoking.

RESULTS

Twenty-five smokers and age-matched nonsmokers (all men; mean age, 29 years) were studied. Collagen-induced platelet aggregation and plasma/urinary thromboxane B2 (TXB2) and 11-dehydroxythromboxane B2 levels were higher in cigarette smokers compared to nonsmokers. Greater expression of platelet COX-1 was observed in smokers than in nonsmokers. Among smokers, collagen-induced platelet aggregation correlated positively with platelet volume and circulating nicotine and cotinine concentrations. The levels of plasma/urinary TXB2 were significantly increased an hour after cigarette smoking.

CONCLUSION

Cigarette smoking aggravates COX-1-mediated platelet reactivity in young, otherwise healthy, smoking men.

Up-regulation of G-protein-coupled receptors for endothelin and thromboxane by lipid-soluble smoke particles in renal artery of rat

Up-regulation of G-protein-coupled receptors (GPCR) plays key roles in renal hypertension and cardiovascular disease pathogenesis. The present study was designed to examine if lipid-soluble cigarette smoking particles (DSP), nicotine and endotoxin (LPS), induce GPCR up-regulation for thromboxane A(2) (TP), endothelin type A (ET(A) ) and type B (ET(B) ) receptors in renal artery, and if intracellular signal mechanisms are involved. Renal artery segments of rats were exposed to DSP, nicotine or LPS, in organ culture for up to 24 hr. The GPCR-mediated contractions were recorded by using a myograph system. Expression of the GPCR was examined by real-time PCR and immunohistochemistry at mRNA and protein levels. Sarafatoxin 6c (S6c, selective ET(B) receptor agonist), endothelin-1 (ET-1, non-selective ET(A) and ET(B) receptor agonist) and 9,11-Dideoxy-9a,11a-methanoepoxy prostaglandin F(2a) (U46619, a TP receptor agonist) induced contractions were significantly increased after the arterial segments exposed to DSP in a concentration-dependent (0.1-0.4 μl/ml) manner, and S6c also induced a time-dependent contraction, compared to control (dimethyl sulfoxide). This was in parallel with enhanced mRNA expression for ET(B) receptor but not ET(A) and TP receptors, while increased protein expression for ET(A) , ET(B) and TP receptors was seen. The specific nuclear factor-kappa B (NF-κB) signal pathway inhibitor BMS345541 was applied to link DSP effects to the GPCR up-regulation. It totally abolished ET(B) receptor up-regulation, but not ET(A) and TP receptor up-regulations. Our results suggest that DSP transcriptionally up-regulated ET(B) receptor expression in rat renal artery via NF-κB signal pathways, whereas up-regulation of ET(A) and TP receptor-mediated contraction may involve post-transcriptional mechanisms.

Up-regulation of thromboxane A2 receptor expression by lipid soluble smoking particles through post-transcriptional mechanisms

Atherosclerosis is a key factor in vascular disease, and cigarette smoking is a well-known risk factor that may induce an inflammatory response and enhance plaque formation in arteries. Thromboxane (Tx) is one key inflammatory mediator involved in the pathogenesis of cardiovascular disease. The present study was designed to test if lipid soluble smoking particles (DSP) enhance TxA(2) receptor (TP) expression in rat mesenteric arteries, and if intracellular mitogen-activated protein kinase (MAPK) pathways play a role. Organ culture of rat mesenteric arteries in the presence of DSP (0.2 microl/ml for 24h) resulted in markedly elevated contractile responses to the Tx analog U46619, compared with the control DMSO. There was no increase in TP receptor mRNA expression, while the protein expression was significantly enhanced. This up-regulation was not affected by a general transcriptional inhibitor actinomycin D, but was almost completely abolished by cycloheximide, a general translational inhibitor. Dexamethasone, a glucocorticoid, manifested a potent inhibitory effect as well. These results suggest that the up-regulation of TP receptor occurs via post-transcriptional events, and mainly translation. This is supported by experiments with specific inhibitors for c-Jun-NH(2)-terminal kinase (SP600125), extracellular signal-regulated kinase 1 and 2 (PD98059 and U0126) and p38 (SB203580) that had no inhibitory effect on the up-regulation of TP receptors. Collectively, the results show that MAPK pathways are not involved in TP receptor up-regulation. Study on TP receptor mRNA stability showed that during organ culture, the TP receptor mRNA was stable in both DMSO and DSP group, but the latter elicited a tendency to stabilize the TP receptor mRNA at higher level. Thus, post-transcriptional mechanisms are responsible for the up-regulation of TP receptor by DSP, in which enhanced translation is the major cause of the elevated protein expression and the enhanced contraction.

Smoking before pregnancy and risk of gestational hypertension and preeclampsia

OBJECTIVE

Our purpose was to determine whether smoking before pregnancy reduces the risk of gestational hypertension or preeclampsia.

STUDY DESIGN

The trial of Calcium for Preeclampsia Prevention (CPEP) was a randomized study of 4589 nulliparous women conducted in 5 US medical centers during the years 1992 through 1995. Women were classified into 4 exposure groups by smoking history obtained at study enrollment (13-21 weeks' gestation): (1) never smoked, (2) smoked but quit before the last menstrual period (LMP), (3) smoked but quit after LMP but before enrollment, and (4) smoked and still smoking at enrollment.

RESULTS

After adjustments were made for maternal age, race, body mass index, type of health insurance, and clinical center, women smoking at enrollment had a reduced risk of hypertension (relative risk = 0.8; 95% CI, 0.6-0.9). Women who quit smoking before the LMP did not have reduced risk (relative risk = 1.1; 95% CI, 0.9-1.3). Results were similar for gestational hypertension and preeclampsia examined separately.

CONCLUSION

Women who smoke but quit before becoming pregnant do not have a reduced risk for gestational hypertension or preeclampsia.

Cigarette smoking during pregnancy and risk of preeclampsia: a systematic review

In this systematic review of the existing evidence regarding the relationship between cigarette smoking during pregnancy and preeclampsia, studies were found through searches of MEDLINE (1966-October 31, 1998), Embase, Popline, CINAHL, Lilacs, bibliographies of identified studies, and proceedings of meetings on preeclampsia, and also through contact with relevant researchers. No language restrictions were imposed. Only cohort and case-control studies dealing with the relationship between cigarette smoking and preeclampsia were considered. Assessment of methodologic quality and data extraction of each study were carried out by 2 authors working independently. Typical relative risks and odds ratios with 95% confidence intervals were calculated for cohort and case-control studies, respectively, with both fixed and random effects models. Twenty-eight cohort studies and 7 case-control studies including a total of 833,714 women were included. All cohort studies reported an inverse association between cigarette smoking during pregnancy and incidence of preeclampsia (typical relative risk, 0.68; 95% confidence interval, 0.67-0.69). The findings were similar for case-control studies (typical odds ratio, 0.68; 95% confidence interval, 0.57-0.81). An inverse dose-response relationship was also found. Pooled data from cohort and case-control studies showed a lower risk of preeclampsia associated with cigarette smoking during pregnancy.

Augmented myocardial ischaemia by nicotine--mechanisms and their possible significance

1. To study the effect of nicotine on the severity of experimental myocardial ischaemia, Langendorff hearts of rabbits (n=7-12 per group) were subjected to 2 h of low-flow ischaemia followed by 1 h of reperfusion. 2. Infusion of nicotine (100 ng ml(-1)) caused only minor changes in non-ischaemic conditions but a significant (P<0.05) increase in end-diastolic pressure (LVEDP), loss of creatine kinase (CK) and troponin (TnT) as well as increase in noradrenaline (NA) overflow in reperfused ischaemic hearts. 3. RT PCR was done on total RNA for mRNA expression of the constitutive (COX-1) and inducible cyclooxygenase (COX-2). There was no COX-2 in non-ischaemic hearts but a significant expression in ischaemia (n=5) which was further increased by nicotine. These data were confirmed at the protein level by Western blotting and additionally shown that COX-1 remained unchanged. 4. There was a marked increase in prostacyclin (PGI2) and a 2 fold increase in NA overflow which were both stimulated by nicotine. 5. The aggravating effects of nicotine on myocardial ischaemia (CK release) as well as the expression of COX-2 mRNA were prevented by pretreatment with the beta-blocker pindolol (1 microM). 6. The data demonstrate marked deleterious actions of nicotine in reperfused ischaemic hearts. These actions are probably related to the increase in catecholamine overflow, are beta-receptor-mediated and involve enhanced gene expression of COX-2.

Nicotine stereoisomers and cotinine stimulate prostaglandin E2 but inhibit thromboxane B2 and leukotriene E4 synthesis in whole blood

The effects of (-)-nicotine (0.0005-500 microM), (+)-nicotine (0.0005-50 microM) and (-)-cotinine (0.0005-500 microM) on arachidonic acid metabolism were investigated in Ca2+ ionophore A23187 (calcimycin)-stimulated human whole blood in vitro. (-)-Nicotine and (-)-cotinine stimulated prostaglandin E2 but inhibited thromboxane B2 synthesis, as has been observed previously in A23187-stimulated polymorphonuclear leukocytes and platelet-rich plasma [Saareks, V., Riutta, A., Mucha, I., Alanko, J., Vapaatalo, H., 1993. Nicotine and cotinine modulate eicosanoid production in human leukocytes and platelet rich plasma. Eur. J. Pharmacol., 248, 345-349.]. (+)-Nicotine also stimulated prostaglandin E2 but inhibited thromboxane B2 synthesis. High concentrations of (-)-nicotine and (-)-cotinine and even nanomolar concentrations of (+)-nicotine inhibited leukotriene E4 synthesis. These results indicate that (-)-nicotine and (-)-cotinine stimulate cyclooxygenase but inhibit thromboxane synthase and 5-lipoxygenase in whole blood in vitro. (+)-Nicotine is capable of affecting in the same direction as well.

Cigarette smoke-induced bronchoconstriction: causative agents and role of thromboxane receptors

Inhalation of cigarette smoke induces a biphasic bronchoconstriction in guinea pigs: the first phase is induced by a combination of cholinergic reflex and tachykinins, whereas the second phase involves cyclooxygenase metabolites (J.-L. Hong, I. W. Rodger, and L.-Y. Lee. J. Appl. Physiol. 78: 2260-2266, 1995). This study was carried out to further determine the causative agents in the smoke and the types of prostanoid receptors and endogenous prostanoids mediating the bronchoconstriction. Inhalation of 10 ml of high-nicotine cigarette smoke consistently elicited the biphasic bronchoconstriction in anesthetized and artificially ventilated guinea pigs. Pretreatment with hexamethonium (10 mg/kg iv) significantly reduced the first-phase bronchoconstriction but did not have any measurable effect on the second-phase response. In sharp contrast, gas-phase smoke did not elicit any bronchoconstrictive effect. Furthermore, when the animals were challenged with low-nicotine cigarette smoke, only a single second-phase response was evoked, accompanied by increases in thromboxane (Tx) B2 (a stable metabolite of TxA2), prostaglandin (PG) D2, PGF2 alpha in the bronchoalveolar lavage fluid. The bronchoconstrictive response induced by low-nicotine smoke was completely prevented by pretreatment with SQ-29548 (0.3 mg/kg iv), a TxA2-receptor antagonist. These results indicate that 1) nicotine is the primary causative agent responsible for the first-phase bronchoconstriction and 2) nonnicotine smoke particulates evoke the release of TxA2, PGD2, and PGF2 alpha, which act on TxA2 receptors on airway smooth muscles and induce the second-phase response to cigarette smoke.

Effect of antiestrogen regimen on prostacyclin and thromboxane A2 in postmenopausal patients with breast cancer: evidence of significance of hypertension, smoking or previous use of estrogen therapy

To explore the mechanism(s) by which antiestrogens may protect against the development of cardiovascular disorders, we measured the production of vasodilatory, antiaggregatory prostacyclin (PGI2) and that of vasoconstrictive, proaggregatory thromboxane A2 (TxA2) before and after 6 months' use of antiestrogens in postmenopausal patients after operation for stage II breast cancer (n = 38). Urine samples were assayed by high performance liquid chromatography and radio-immunoassays for 2,3-dinor-6-ketoprostaglandin F1 alpha (= metabolite of PGI2, dinor-6-keto) and for 2,3-dinor-thromboxane B2 (= metabolite of TxA2, dinor-TxB2). In addition, in 35 of these 38 patients we assayed the capacity of platelets to produce thromboxane A2 during standardized blood clotting. The 4 patients using low-dose aspirin had low thromboxane production, and were excluded from further analysis of the data. An antiestrogen regimen consisting either of tamoxifen (n = 15) or of toremifene (n = 19) caused no changes in production of PGI2 or TxA2, or in their ratio, and in this regard, these antiestrogens behaved similarly. Hypertensive patients (n = 7) using different anti-hypertensive agents were characterized by reduced urinary out-put of dinor-6-keto (18.5 +/- 6.1 vs 35.5 +/- 18.5 ng/mmol, mean +/- SD, p < 0.05) and reduced platelet capacity to produce TxA2 (62.6 +/- 67.8 vs 134.6 +/- 75.6 ng/mL, p < 0.05). The patients (n = 15) who had used estrogen replacement therapy (ERT) up until diagnosis of breast cancer showed reduced dinor-TxB2 excretion (15.5 +/- 12.7 vs 29.9 +/- 20.9 ng/mmol, p < 0.05) before initiation of antiestrogens, and elevated dinor-6-keto output during the antiestrogen regimen (32.4 +/- 21.2 vs 22.7 +/- 8.7 ng/mmol, p = 0.07). Smokers (n = 6) had elevated dinor-TxB2 output before and during antiestrogen use. Thus we conclude that the cardiovascular protection provided by an antiestrogen regimen is unlikely to be mediated through vaso- and platelet active PGI2 and TxA2.

Nicotine and cotinine modulate eicosanoid production in human leukocytes and platelet rich plasma

We investigated the effects of nicotine and cotinine (0.5 nM-0.5 mM) on prostaglandin E2 and leukotriene B4 production in human polymorphonuclear leukocytes and on thromboxane B2 formation in human platelet-rich plasma, stimulated by calcium ionophore A23187. Nicotine and cotinine dose-dependently increased prostaglandin E2 synthesis in polymorphonuclear leukocytes from 25% (0.5 nM) up to nearly four-fold (0.5 mM). In concentrations found in the plasma of smokers, nicotine and cotinine increased prostaglandin E2 production by 33% (50 nM) and 50% (500 nM), respectively. Nicotine and cotinine equipotentially reduced both leukotriene B4 production in polymorphonuclear leukocytes and thromboxane B2 production in platelet rich plasma, the inhibition increasing from 20% (0.5 nM) to 60% (0.5 mM). The stimulation of prostaglandin E2 and inhibition of leukotriene B4 and thromboxane B2 production by nicotine and cotinine may due to the pyridine moiety that these compounds have in common.

Effects of cigarette smoking on the function of metabolizing arachidonic acid and angiotensin I in the isolated perfused rat lungs

The effects of acute and chronic cigarette smoking on the metabolism of exogenous arachidonic acid (AA) and angiotensin I (AI) in perfused isolated rat lungs were studied. The results showed that acute cigarette smoking did not alter the contents of 6-keto-PGF1 alpha (the stable metabolite of PGI2) and TXB2 (the stable metabolite of TXA2) in the effluent and the increment of pulmonary artery pressure (delta Ppa) caused by AA. The conversion of A I into A II was significantly increased (P < 0.01), while the delta Ppa induced by A I injection was obviously decreased as compared with controls (P < 0.05). After cigarette smoke exposure for 30 days, the delta Ppa caused by AA or A I did not differ from that of controls, but the contents of 6-keto-PGF1 alpha and A II increased more markedly than those in non-smoking rats (P < 0.05). It is suggested that acute and chronic cigarette smoking in rats can promote the lung function of converting A I into A II, chronic smoking can increase the lung function of metabolizing AA into PGI2.

The role of prostaglandins in obstetrical disorders

All pregnancy-associated tissues are capable of producing prostaglandins including PGI2 and TXA2. In normal pregnancy there is a dominance of PGI2 over TXA2 which may contribute to the maternal circulatory adaptation to pregnancy. Furthermore, both fetoplacental PGI2 and TXA2 production are important regulators of the fetal blood supply. It has been clearly established that in pre-eclampsia PGI2 production decreases in the fetoplacental tissues and quite probably also in the maternal tissues. The effect of this change may be further exaggerated by the simultaneous stimulation in pre-eclampsia of TXA2 production. The reason for PGI2 deficiency is not known. Other vasoactive agents, such as endothelin, may act in concert with prostaglandins. Relative PGI2 deficiency is likely to exist also in IUGR and lupus anticoagulant syndrome of pregnancy. In the latter, lupus anticoagulant may directly inhibit the synthesis of PGI2. One study suggests PGI2 deficiency also in early pregnancies of women with a history of repeated abortions. Prostaglandin production increases during full-term labour, and similar but smaller changes also occur in preterm labour. A silent bacterial infection may trigger the onset of preterm labour through cytokine-stimulated increase of prostaglandin production. No data were found on prostaglandin production in post-term pregnancies. That oligo-polyhydramnios is possibly prostaglandin mediated is suggested by the control of polyhydramnios by indomethacin treatment. Smoking decreases the production of PGI2 and possibly increases that of TXA2, which may lead to decreased blood flow and IUGR. Which constituent of cigarette smoke exerts this effect is not known. Ethanol consumption causes aberrations in prostaglandin metabolism which cannot be directly connected with fetal alcohol effects.

Arachidonic acid metabolism in nicotine-treated rats and nicotine-incubated rabbit aortic smooth muscle cells

1. The changes in plasma levels of thromboxane-B2 (TXB2) and 6-keto-prostaglandin-F1 alpha (6-keto-PGF1 alpha) were examined in rats given 5, 25, 50 or 100 micrograms/mL nicotine in drinking water for 10 days. 2. The effect of nicotine on prostacyclin (PGI2) synthesis from endogenous arachidonic acid by cultured rabbit aortic smooth muscle cells was also studied. 3. Plasma levels of TXB2 were increased dose-dependently by treatment for 10 day with nicotine. 4. 6-Keto-PGF1 alpha values were lowered dose-dependently, both in the plasma of nicotine-treated rats and in rabbit aortic smooth muscle cells incubated with the alkaloid. 5. The results suggest that endogenous synthesis of thromboxane-A2 and PGI2, as reflected by TXB2 and 6-keto-PGF1 alpha levels, respectively, is influenced by nicotine treatment. These findings may be related to cardiovascular diseases associated with cigarette smoking, but further studies are needed.

[Influence of cigarette smoking on the hypoxic pulmonary vasoconstriction in isolated rat lungs--the role of prostaglandins and leukotrienes]

Isolated rat lungs perfused with blood were used to determine the effects of cigarette smoke, delivered into the lung by a ventilator, on the pulmonary vascular resistance (PVR), and on the hypoxic pulmonary vasoconstriction (HPV), and to explore the role the prostaglandins (PG) and leukotrienes (LT) play in that effect. The results showed that PVR did not change, while HPV was significantly enhanced by smoking. Indomethacin, an inhibitor of PG biosynthesis, administered in the perfusing blood (20 micrograms/ml) increased HPV in non-smoking lungs, but not in lungs after smoking. Diethylcarbamazine citrate (DEC; 1 mg/ml), an inhibitor of LT biosynthesis, decreased HPV before and after smoking. After perfusion with both indomethacin and DEC, HPV also decreased. It is suggested that LT act as mediators whereas PG as modulators in HPV, and PG and LT might play an important role in the increase of HPV by cigarette smoking.

The in vitro effects of nicotine and cotinine on prostacyclin and thromboxane biosynthesis

The comparative effects of nicotine and cotinine on the biosynthesis of prostacyclin (PGI2) and thromboxane A2 (TXA2) in the horse aorta and platelet microsomes were studied. TXB2 and 6-keto PGF1a stable metabolites of TXA2 and PGI2 respectively were determined by radioimmunoassay. TXA2 production in the presence of either nicotine or cotinine treatment was not altered. However, a dose dependent inhibition of PGI2 biosynthesis, and a dose dependent stimulation of PGI2 biosynthesis, was observed in the presence of nicotine and cotinine respectively. Moreover, cotinine (10b3 M) was able to prevent the inhibitory effect of nicotine on PGI2 synthetase when preincubated with horse aorta microsomes. It appears that cotinine, the major nicotine metabolite resulting from a breakdown process, could be useful for the organism, at least for the cardiovascular system.

Effects of acrolein on human platelet aggregation

Acrolein, a component of tobacco smoke, potentiated platelet aggregation and increased thromboxane A2 (TXA2) formation caused by thrombin and arachidonic acid (AA). Acrolein produced these effects at concentrations in the range 50-5000 microM. Acrolein had no effect on platelet responses to ADP, epinephrine, collagen or the ionophore A23187. Acrolein increased the mobilization of [3H]arachidonic acid from prelabelled platelets in response to thrombin and arachidonic acid. The increased availability of substrate could partly explain the enhanced production of TXA2 and increased aggregation observed in the presence of acrolein. These findings could provide an explanation for the increased incidence of vascular disease in cigarette smokers.

Relative participation of the gas phase and total particulate matter in the imbalance in prostacyclin and thromboxane formation seen following chronic cigarette smoke exposure

Chronic exposure to cigarette smoke causes an imbalance in the ratio of PGI2 and TXA2 production and is believed to favor the development of atherosclerosis. Components of the particulate phase of smoke (especially nicotine) as well as the gas phase of smoke have been shown to adversely alter arachidonic acid metabolism. To determine the relative participation of nicotine, particulate and gas phases in eliciting an imbalance in TXA2 formation, male Sprague-Dawley rats were chronically exposed (7 days/wk/mo.) to freshly generated whole smoke or gas phase from University of Kentucky Reference cigarettes and allowed access to regular drinking water or to water supplemented with nicotine (10 micrograms/ml). COHb levels were monitored to confirm smoke or gas phase inhalation. All treatment groups had lower body weights than shams. No differences in body weights were observed between smoke (+/- oral nicotine) and gas phase (+/- oral nicotine) treatment groups but all were significantly lower than oral nicotine treated animals. Platelet TXA2 production was elevated in all treatment groups compared to shams. No differences in TXA2 production were observed between smoke (+/- oral nicotine), gas phase and oral nicotine treated animals. Animals receiving gas phase/oral nicotine exhibited significantly higher platelet TXA2 production compared to the other treatments. Constituents of the gas phase as well as the particulate phase of whole smoke were both shown to elevate platelet TXA2 formation. Components of the particulate matter appear to modulate the effects of nicotine and the gas phase in the perturbation of TXA2 production in the rat smoking model.

Prostacyclin and thromboxane formation following chronic exposure to cigarette smoke condensate administered via osmotic pumps in rats. A method for chronic administration of particulates of whole smoke

Chronic cigarette smoke exposure in vivo causes decreased conversion of [14C]arachidonic acid (AA) to prostacyclin (PGI2) by isolated aortic tissue and increased conversion to thromboxane (TXA2) by isolated platelets from rats. Alterations in the PGL2/TXA2 balance may be part of the mechanism by which smoking increases the risk of cardiovascular disease. In order to ascertain whether the particulate phase of whole smoke alone could cause these changes, rats were administered smoke condensate in propylene glycol for 56 days via two Alzet (2ML4) osmotic pumps. Pumps containing vehicle, low dose (150 micrograms/hr) or high dose (300 micrograms/hr) condensate were implanted s.c. dorsal to the thoracic vertebrae in male Sprague-Dawley rats. Three-quarters of the condensate-treated rats developed fibrin cysts encapsulating the pumps. Cysts were not seen in vehicle-treated rats. Residual pump contents were weighed and analyzed by GLC to ensure condensate delivery. No significant difference in weight gain patterns between sham-operated and treatment groups were observed. Vehicle had no effect on aortic PGI2 or platelet TXA2 formation compared to sham. Low-dose condensate was without effect on PGI2/TXA2 formation. In high-dose condensate-treated rats, PGI2 and TXA2 formation were 84% and 136%, respectively, of the vehicle control (n.s.). Pump encapsulation may be a limiting factor in the administration of complex particulate suspensions.

Magnesium and other nutrient deficiencies as possible causes of hypertension and low birthweight

7.2 per cent of babies born in England and Wales in 1986 had birthweights below 2,500 g. Low birthweight and hypertension are associated. European trials have reported that oral supplementation with physiological amounts of magnesium during pregnancy reduces pregnancy hypertension and also miscarriage, preterm birth and fetal growth retardation. Magnesium deficiency causes hypertension and low birthweight in animals. In humans deficiency of thiamin and other B vitamins has also been reported to cause pregnancy hypertension and low birthweight. Magnesium and B vitamins are essential for the same biochemical reactions in energy metabolism. There is evidence that magnesium consumption of substantial numbers of women in Europe and North America is too low to support a healthy pregnancy. Magnesium and thiamin are lost in processing many foods. British trials of magnesium supplementation are advocated. It is suggested that more attention should be given to magnesium in nutritional advice.