Alpha-2-adrenoreceptor density on intact platelets and adrenaline-induced platelet aggregation in endurance- and nonendurance-trained subjects.

Alpha-2-adrenoreceptor density on intact platelets was evaluated in 17 sportsmen, 8 of whom were endurance-trained athletes. Receptor density was determined as being equivalent to 3H-Yohimbine, specifically bound on intact platelets. Adrenaline-induced aggregation of platelets in vitro was additionally ascertained. Bmax (maximal binding) and KD (dissociation constant) were significantly lower in endurance-trained athletes (148 fmol per 10(9) platelets, KD = 0.92 nmol) than in the nine nonendurance-trained individuals (284 fmol, KD = 1.79 nmol, P less than 0.01), amounting to 89 receptors per cell (endurance-trained subjects) and 171 (nonendurance-trained subjects). No significant change of receptor density or affinity was observed subsequent to exhaustive exercise in the group of eight endurance-trained individuals. Bmax values and oxygen uptake capacity correlated negatively (r = -0.78, P less than 0.001) and Bmax values and induced platelet aggregation in vitro positively (r = 0.79, P less than 0.001). Data may indicate a reduced sensitivity of platelets in endurance-trained subjects.

[Free and conjugated plasma catecholamines, lactate behavior and oxygen uptake at rest and in staged physical exertion as well as alpha receptor density in intact thrombocytes in trained athletes]. / Freie und konjugierte Plasmakatecholamine, Laktatverhalten und Sauerstoffaufnahme in Ruhe und während stufenweiser Körperarbeit sowie Alpha-Rezeptoren-Dichte an intakten Thrombozyten bei Kraftsportlern.

The influence of chronic static training on free and conjugated plasma catecholamines was investigated in 8 statically trained athletes (21 +/- 2 years of age) at rest and during incremental ergometric cycling. Plasma catecholamines are seen as biochemical indicators of the over-all sympathetic activity. Alpha-2-adrenoreceptors were additionally determined as one parameter of the organism's sensitivity to catecholamines. During modest and heavy exercise, free plasma noradrenaline and adrenaline are comparably low in statically and endurance trained athletes. They are lower than in untrained subjects. During exhaustion, however, free adrenaline responses of the statically trained athletes only amount to 30-50% of the concentrations observed in endurance trained athletes and untrained subjects. Free plasma dopamine and conjugated plasma catecholamines do not show any significant changes during ergometric exercise. Free and conjugated catecholamines correlate positively. Positive correlations are also observed between blood pressure and plasma catecholamines. These correlations however are clearer between conjugated catecholamines and blood pressure. This is also recognizable for the negative correlation between alpha-2-receptor density on intact platelets (1078 +/- 323 binding sites per cell) and conjugated catecholamines. In conclusion, statically trained athletes also show an alteration of sympathetic tone (catecholamines) comparable to that observed in endurance trained athletes. Maximal adrenaline responses however are lower in statically trained athletes than in endurance trained or untrained subjects. The alpha-adrenoreceptor density on intact thrombocytes seems to be increased in statically trained athletes.

[Is the alpha adrenergic receptor density increased in intact thrombocytes in non-isometric trained athletes?]. / Ist die Alpha-Adrenorezeptorendichte an intakten Thrombozyten bei statisch trainierten Athleten erhöht?

Alpha-adrenoreceptors were determined as an equivalent to 3H-dihydroergocryptine (DHE) specifically bound on intact thrombocytes in five untrained volunteers (I), eight non-staticly trained sportsmen (II), and eight intensively staticly trained athletes (III). Bmax was 933 +/- 363 (I), 982 +/- 373 (II), and 1796 +/- 539 fmol DHE X 10(-9) thrombocytes (III). KD was 1.28 +/- 0.49 (I), 2.94 +/- 1.12 (II), and 3.58 +/- 1.07 nmol X l-1 (III). The number of binding sites per cell amounted to 561 +/- 202 (I), 589 +/- 224 (II), and 1078 +/- 323 (III). The thrombocytes of the staticly trained athletes showed a significantly higher number of binding sites and a slightly higher affinity (KD) than the other groups (p less than 0.01). However, a wide range of overlapping has to be considered. The biologic significance of these results and their transferability to other organs are open at present. It is the question whether an altered adrenoreceptor density may be one factor of a higher prevalence of hypertension in staticly trained athletes on which our research group has reported recently.

[Determination of beta-receptors on intact polymorphonuclear leukocytes in autologous plasma]. / Bestimmung von beta-Rezeptoren an polymorphkernigen intakten Leukocyten im autologen Plasma.

The binding of tritium labelled radioligand dihydroalprenolol was investigated on live polymorphonuclear leukocytes of 6 endurance trained (VO2 max. 65.7 +/- 2.0 ml/kg . min), and 9 non-endurance trained subjects (VO2 max. 52.0 +/- 4.0 ml/kg . min). The specific binding of dihydroalprenolol is seen as an indicator of the beta-receptor density. The specific binding of dihydroalprenolol is defined as the difference between the total binding and that amount of dihydroalprenolol that could not be displaced. The leukocytes were reincubated for the binding studies in their autologous plasma. The specific binding of dihydroalprenolol on live polymorphonuclear leukocytes shows a levelling off behaviour at a concentration of approximately 2 nmol/l dihydroalprenolol in trained as well as in untrained subjects. The specific binding amounts to about 85% (0.1 nmol/l dihydroalprenolol) to 51% (2.0 nmol/l dihydroalprenolol) of the total binding. Based on Scatchard analysis, Bmax was determined as 41.2 fmol/10(7) cells (trained subjects) and 21.6 fmol/10(7) cells (untrained subjects). KD is 0.44 nmol/l dihydroalprenolol (untrained subjects), and 0.49 nmol/l dihydroalprenolol (trained subjects). The beta-adrenergic binding sites are approximately 1300 (untrained subjects), and 2500 binding sites/cell (trained subjects). The specific binding of dihydroalprenolol on live polymorphonuclear leukocytes is significantly higher in trained than in untrained subjects. This training dependent change in beta-receptor density may be an indicator of an increased sensitivity to catecholamines.