Maintained hyperexcretion of thromboxane A2 metabolite in healthy young cigarette smokers: results from a prospective study in randomly sampled males with stable smoking habits.

Although several studies have identified cigarette smoking as a factor increasing platelet formation of thromboxane A2 (TxA2), no prospective data on this issue have been presented in a defined population with stable smoking habits. Therefore, we analysed the relation between smoking habits and urinary excretion of the 2,3-dinor metabolites of thromboxane A2 (Tx-M) and prostacyclin (PGI-M) in 87 males, randomly sampled from a population of 18-19-year-old men, at two different occasions separated by 31-49 months. The daily cigarette consumption among the smokers was unchanged between the study occasions (11 vs. 11 cigarettes day-1), but 9 of 43 initial smokers had quit. None of the initial non-smokers had begun smoking. Tx-M was higher in the smokers than in the non-smokers and correlated with the daily cigarette consumption both at the initial (176 vs. 123 pg mg-1 creatinine; P = 0.01) and the second (214 vs. 164 pg mg-1; P = 0.002) study occasion. Those who had quit smoking since the initial study did not differ in Tx-M from the non-smokers at the second study occasion. Urinary PGI-M did not differ between cigarette smokers, non-smokers and quitters at either of the study occasions. We conclude that cigarette smoking elicits an increased formation of thromboxane A2, indicating platelet activation, that is stable during an observation period of up to 4 years. The increased platelet activity is reversible upon quitting.

Tobacco use and urinary excretion of thromboxane A2 and prostacyclin metabolites in women stratified by age.

BACKGROUND: Activated platelets have been implicated in both acute thrombus formation and atherogenesis. Because smoking is a risk factor for cardiovascular disease in men and women and male smokers have biochemical evidence of increased platelet activation, we found it of interest to study whether smoking augments platelet activity in women as well. METHODS AND RESULTS: Data on smoking habits and a urinary sample were obtained from 125 healthy female nonsmokers and an equal number of smokers, stratified by age in five groups from 18 to 59 years old. Urinary samples were analyzed with gas chromatography/mass spectrometry for the 2,3-dinormetabolites of thromboxane A2 (Tx-M), reflecting platelet activity, and prostacyclin (PGI-M), representing platelet/vessel wall interaction. Urinary Tx-M in smokers was higher than in nonsmokers (p < 0.001), increasing with the number of cigarettes smoked per day and with age. In nonsmokers, there was no difference in Tx-M between the age groups. Urinary PGI-M in smokers was higher than that in nonsmokers (p < 0.001) and decreased with age in nonsmokers but not in smokers. There was no difference in Tx-M between previous smokers and lifelong nonsmokers. CONCLUSIONS: The elevated Tx-M in women who smoke cigarettes indicates an increased platelet activity that is dependent on smoking intensity. In parallel, PGI-M is augmented, suggesting that platelet/vessel wall interaction is stimulated. Quitting smoking is an effective means to restore platelet function. We propose that the observed increase in platelet activity in women who smoke cigarettes may be related to subsequent development of cardiovascular disease and that quitting smoking should be considered a high-priority medical target also in this sex.

2,3-Dinor metabolites of thromboxane A2 and prostacyclin in urine from healthy human subjects: diurnal variation and relation to 24h excretion.

1. Urinary levels of the 2,3-dinor metabolites of thromboxane A2 (2,3-dinor-thromboxane A2, Tx-M) and prostacyclin (2,3-dinor-6-keto-prostaglandin F1 alpha, PGI-M) are frequently analysed as indices of platelet and endothelial activity and interaction in vivo. Despite this, little is known about the possible diurnal variations in urinary Tx-M and PGI-M in healthy human subjects, and how the urinary levels of Tx-M and PGI-M in single samples reflect their respective 24 h excretion rates. We addressed this by determining Tx-M, PGI-M and creatinine in consecutive portions of urine collected during 24 h in 15 healthy non-smoking subjects. 2. The total 24 h excretion of Tx-M and PGI-M did not differ between men (223 +/- 31 and 132 +/- 27 ng, respectively) and women (215 +/- 44 and 127 +/- 29 ng, respectively). Neither the excretion of Tx-M nor that of PGI-M displayed any significant diurnal variation. 3. The excretion of Tx-M during a 3 h period and the Tx-M/creatinine ratio in a urine sample accurately reflected the 24 h excretion of Tx-M (correlation coefficient ranges 0.74-0.94 and 0.74-0.86, respectively). The excretion of PGI-M during a 3 h period and the PGI-M/creatinine ratio in a urinary sample were accurate measures of 24 h excretion of PGI-M (correlation coefficient ranges 0.76-0.94 and 0.72-0.83, respectively). Urinary Tx-M and PGI-M expressed as simple concentrations were poor indices of their respective 24 h excretion. 4. We conclude that time-related excretions of Tx-M and PGI-M may be the best indices ex vivo of the cardiovascular formation of thromboxane A2 and prostacyclin, but that urinary creatinine-related concentrations of Tx-M and PGI-M in a urine sample are accurate measures as well.

Relation between tobacco use and urinary excretion of thromboxane A2 and prostacyclin metabolites in young men.

BACKGROUND: Cigarette smoking is a risk factor for cardiovascular disease. The present study addressed the effect of tobacco use on the formation of two eicosanoids, thromboxane A2 and prostacyclin, which have been implicated in both acute and chronic cardiovascular disorders. METHODS AND RESULTS: In 577 randomly sampled 18-19-year-old men, the urinary excretion of the 2,3-dinor metabolites of thromboxane A2 and prostacyclin (Tx-M and PGI-M, respectively) was analyzed and related to the subjects' self-reported use of tobacco. Sixty-five percent of the subjects used no tobacco, 7.5% were cigarette smokers, 22% used wet (oral) snuff, and the rest reported a mixed use of tobacco. The urinary excretion of Tx-M was higher (p less than 0.001) in cigarette smokers than in those not using tobacco (180 versus 128 pg/mg creatinine) and was correlated (r = 0.35, p less than 0.05) with the daily cigarette consumption. Snuff users had no increase in their urinary excretion of Tx-M, despite urinary cotinine levels comparable to those in the cigarette smokers (1,210 and 1,560 ng/ml, respectively). The excretion of PGI-M did not differ between non-tobacco users, cigarette smokers, and snuff users. CONCLUSIONS: We conclude that cigarette smoking, but not the use of snuff, facilitates the formation of thromboxane A2. We propose that such an increased formation reflects platelet activation in the absence of vascular injury and that it may be of significance for the subsequent development of cardiovascular disease.

Non-invasive assessment of the cardiovascular eicosanoids, thromboxane A2 and prostacyclin, in randomly sampled males, with special reference to the influence of inheritance and environmental factors.

1. We studied, in a random sample of 385 nonsmoking men born in 1968-1969 and 31 men born in 1913 or 1923, whether inheritance and environmental factors influenced platelet activity and vessel wall prostacyclin formation, as reflected non-invasively by the urinary excretion of the 2,3-dinor-metabolites of thromboxane A2 (2,3-dinor-thromboxane B2, Tx-M) and prostacyclin (2,3-dinor-6-keto-prostaglandin F1 alpha, PGI-M), respectively. 2. Fathers of young men with high platelet activity did not excrete more Tx-M than fathers of young men with low platelet activity. Men born in 1913 or 1923 displayed higher Tx-M (563 versus 128 pg/mg of creatinine, P less than 0.001) and PGI-M (163 versus 130 pg/mg of creatinine, P less than 0.01) excretion than those born in 1968-1969. Excretion of both Tx-M and PGI-M was correlated to the urinary output of noradrenaline and adrenaline. 3. Well-trained subjects did not differ in their excretion of Tx-M or PGI-M from those who did not exercise regularly. A recent acute infection was also unrelated to the excretion of Tx-M or PGI-M. PGI-M excretion was, however, significantly correlated to Tx-M excretion (r = 0.51, P less than 0.001). 4. This study provides the first non-invasive evidence that advancing age and sympathoadrenal tone are positively correlated to platelet activity in randomly sampled men, and that paternal inheritance, physical fitness and recent infection lack correlation to platelet activity.

Slow sodium-free contractures in the frog heart mediated by the sodium-calcium exchange.

1. Sodium-free contractures were studied in myocardial strips from R. pipiens when extracellular sodium (Na+o) was replaced by choline chloride and extracellular free calcium (Ca2+o) was defined with EGTA-buffer. 2. Resting membrane potentials (RMP) were normal in sodium-free solutions with Ca2+o calculated below 1.0 x 10(-9) mol/l. 3. When Ca2+o was subsequently increased from zero to 1.0 x 10(-3) mol/l Na+-free contractures developed slowly with unchanged RMP even at maximum contracture, at which the intracellular ultrastructure is grossly altered. 4. The contractures developed significantly faster in the presence of 3 x 10(-6) mol/l ouabain. 5. In sodium-free solutions La3+ did not influence Ca2+-dependent contractures, apart from causing an increase in time to maximum contracture. 6. It is concluded that sarcolemmal integrity is maintained in frog myocardium treated initially with Na+/Ca2+-free solutions and then with Na+-free medium containing 1 mmol/l Ca2+. 7. Our experiments indicate that sodium-free, Ca2+o-dependent contractures are mediated by the Na+/Ca2+-exchange, operation at higher rates when Na+i is increased. La3+ (1 mmol/l) probably does not compete with Ca2+ at extracellular binding sites of the exchanger. 8. The Na+/Ca2+-exchange may under certain experimental conditions be able to increase Ca2+i to cytotoxic concentrations.

Sodium-free contractures in frog myocardium damaged by catecholamines.

1. Sodium-free contractures were studied in myocardial strips from R. pipiens with extracellular sodium (Na+o) replaced by choline chloride and extracellular calcium (Ca2+o) varied with EGTA-buffer. Normal myocardium was compared with that damaged by adrenaline (ADR) or isoproterenol (ISO). 2. Frog myocardium, damaged by in vivo injections of catecholamines, remained relaxed when exposed to Na+/Ca2+-free solutions. Only in 2 out of 18 experiments were small contractures observed after several hours. 3. Addition of KCN to the Na+/Ca2+-free solution caused small contractures after several hours in 7 out of 10 experiments. 4. The time to maximum Na+-free contractures was correlated to Ca2+o in a dose-dependent manner, but not influenced by catecholamine-induced myocardial damage. 5. Cell injury in the frog heart after in vivo injections of catecholamines does not affect the sarcolemmal Na+/Ca2+-exchange and is not associated with passive leakage of Ca2+ from the extracellular to the intracellular space.

Effect of cyanide and verapamil on sodium-free contractures in the frog heart.

Sodium-free contractures were studied in myocardial strips from R. pipiens with extracellular sodium (Na0+) replaced by choline chloride and extracellular calcium (Ca20+) varied with EGTA buffer. At calculated Ca02+ below 2.8 X 10(-7) mol/l, no contracture occurred in most of the experiments, even in the presence of cyanide. When Ca02+ was above 2.8 X 10(-7) mol/l, relatively short tension transients of up to 80 sec duration could be avoided if the myocardial strip was previously equilibrated for 20 min in a Na+-Ca2+-free solution. Instead, contractures developed slowly within one to several hours. The maximum contracture was dependent on Ca02+ in a dose-response-like pattern. The time-course of contracture development was not affected by verapamil, but KCN significantly increased the rate of resting tension increase. In solutions with normal Na+-Ca2+ content and even in a Na+-Ca2+-free milieu, the cellular ultrastructure was normal. Development of contracture after addition of Ca2+ to the Na+-free solution was combined with ultrastructural damage of the ventricular strip. It is concluded that Na+-free contractures depend on transsarcolemmal net-Ca2+ uptake as a sum of Na-Ca-exchange-dependent Ca2+ uptake and active sequestering of intracellular free calcium Ca2+ mediated by sarcolemmal and probably intracellular Ca2+-ATPases. The negative inotropic effect of the Ca blocker verapamil seems not to be mediated by the Na-Ca exchange.

Heart lesions in the frog at high environmental temperature.

Frogs (R. pipiens) adapted to 12 degrees C were exposed to increased environmental temperature during 2 hr. At 33 degrees C gross heart lesions started to appear in a few cases and at 37 degrees C, 71% of the frogs showed ventricular aneurysms and some died. Critical thermal maximum (CTM) was around 37 degrees C in autumn, winter and early spring, whereas in late spring and summer CTM was at 39 degrees C and during these last-mentioned periods of the year gross heart lesions at high temperature did not start until at 37 degrees C. After 2 hr at 37 and 39 degrees C respectively, ECG-abnormalities occurred indicating myocardial injury. Isolated strips of the heart ventricle from frogs with gross heart lesions showed a deteriorated resistance towards cyanide anoxia as measured by an isometric procedure. The ultrastructure was deranged by the high temperature, the changes mainly involving the mitochondria and the myofibrils. These alterations were focal but depletion of glycogen particles was diffuse. As the high temperature induced changes similar to those provoked by catecholamines, propranolol was given in some frogs before the heat exposure. This beta-adrenoceptor blockade did only reduce some of the abnormal changes by 37 degrees C.

Cardiac lesions in the frog induced by adrenaline.

Adrenaline (A) causes gross lesions of the ventricular wall in frogs living both at 12 degrees and 25 degrees. At 12 degrees the sensitivity of the heart to A is higher than at 25 degrees. Single or multiple ventricular aneurysm, provided by A could not be prevented by propranolol. The resistance of the myocardium towards cyanide anoxia is lowered after A especially at 25 degrees. In preliminary experiments with noradrenaline the same cardiotoxic effects are observed.