Effect of nicotine on rabbit blood platelet aggregation

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

We studied the effects of smoking and nicotine on the production of proaggregatory thromboxane A2 (TxA2), antiaggregatory prostacyclin (epoprostenol, PGI2), and on lipid peroxidation in vivo and in vitro. In the in vivo study, serum concentrations of thromboxane B2 (TxB2), a stable metabolite of TxA2, increased immediately after smoking three cigarettes but not after smoking the equivalent amount of tobacco in a pipe, whereas serum lipid peroxide values did not change in either group. In vitro, nicotine (2 X 10(-3) mol/liter) inhibited pulmonary TxB2 production by 70% and simultaneously stimulated the production of 6-keto-prostaglandin F1 alpha, a stable metabolite of PGI2, by 40%, which suggest that nicotine does not exert its effect at the cyclooxygenase level. During aggregation in platelet-rich plasma, TxB2 production was inhibited by 53% with 2 X 10(-3) mol/liter of nicotine, and during whole blood clotting the inhibition was 34% with 2 X 10(-4) mol/liter of nicotine. Thus the rise in cigarette smokers' serum TxB2 was probably caused by some constituent of cigarette smoke other than nicotine. The increased production of TxA2 following cigarette smoking may provide one explanation for the increased incidence of atherosclerosis and its complications in cigarette smokers.

Effects of smoking on platelets and on plasma thromboxane-prostacyclin balance in man

To determine the influence of brief period of smoking on platelet release and platelet-vessel wall prostaglandins, we studied 13 non-smokers and 15 habitual smokers. Blood samples were collected before and immediately after smoking. Before smoking plasma beta-thromboglobulin levels were similar in the two groups. Plasma levels of thromboxane B2 (TXB2), stable metabolite of TXA2 were slightly higher (124 +/- 43 vs 101 +/- 36 pg/ml) and of 6-keto-PGF1 alpha (stable metabolite of PGI2) lower (39 +/- 23 vs 63 +/- 23 pg/ml) in smokers compared to non-smokers. Immediately after smoking, plasma TXB2 levels increased 197% (P less than 0.05) and plasma 6-keto-PGF1 alpha 44% (P-NS) in non-smokers. Similar increases were not observed in the smoker population, although plasma beta-thromboglobulin levels increased 40%. Platelet TXA2 generations induced by arachidonic acid and thrombin were similar in the two groups. These data show that brief period of smoking stimulates both TXA2 and PGI2 release in the non-smokers. Increase in TXA2 is more than in PGI2. Episodic increase in TXA2 may be a mechanism of vascular injury. Absence of increase in TXA2 and PGI2 with smoking in habitual smokers may reflect tolerance to effects of smoking.