[Blood platelet oxygen consumption in pituitary dwarfs (author's transl)]. / La consommation d'oxygène par les plaquettes de nains hypophysaires.

Oxygen consumption in blood platelets of 14 pituitary dwarfs aged from 2 to 8 years was investigated before and after a 2 months' treatment with growth hormone (GH). No significant difference was found between dwarfs and control subjects in respect of basal platelet oxygen uptake (4.0 +/- 3.8 mmol O2/10(9) platelets/min in dwarfs as against 6.4 +/- 4.1 in controls), but the abrupt increase in oxygen consumption induced by thrombin was significantly reduced in dwarfs (4.3 +/- 4.1) as compared with controls (12.3 +/- 7.6; p less than 0.01). During GH treatment, however, the dwarfs' response to thrombin stimulation was similar to that of controls. Since dwarfs had normal platelet malonyldialdehyde production, it is likely that the mitochondrial component of thrombin-induced high oxygen consumption was deficient. These results suggest that blood platelets may contribute to the protective effect of GH deficiency against atherosclerosis.

In vitro effect of levamisole on oxygen consumption and survival of platelets.

Levamisole at a concentration of 10(-3)M inhibits the oxygen consumption of resting platelets, the thrombin induced burst and the platelet aggregation induced by ADP. At the concentration of 10(-7)M it exerts still an inhibitory activity of the thrombin induced burst, but it does not inhibit neither the basal oxygen consumption nor the platelet aggregation. At every tested concentration platelet survival in the presence of levamisole is comparable to that of controls. Levamisole moreover, together with theophylline and glucagon, shows a synergistic inhibiting influence toward the burst of oxygen consumption. Our data suggest that levamisole may act by producing an enzymatic block of cyclo-oxygenase.

Malonyldialdehyde formation, oxygen consumption, fatty acid composition in newborn platelets stimulated by thrombin.

The release reaction, the formation of malonyldialdehyde (MDA), the pattern of oxygen consumption, and the variation in fatty acid composition after addition of thrombin (1.67 U/ml) have been investigated in newborn platelets, comparing the obtained data with analogous values showed by adult platelets assumed as normal controls. Newborn platelets showed a release reaction 20% lower than that of controls. MDA formation, even in the presence of NEM and the burst in oxygen consumption, resulted to be similar in newborn and adult platelets (p greater than 0.3); the burst was also similar after the addition of thrombin (10 U/ml) in the presence of antimycin and aspirin. The ratio between formed MDA and oxygen consumption was 1:10 in adult platelets while it was 1:15 in those of newborns. The study of fatty acid composition demonstrated that in newborn platelets at rest, arachidonic acid is significantly in a higher concentration than in controls and that it decreases after stimulation with thrombin. It is concluded that the pathway of prostaglandins is normally stimulated by thrombin in newborn platelets.