Summary
The authors previously reported a transient decrease in adhesive platelet count and
an enhancement of blood coagulability after administration of a small amount of adrenaline
(0.1-1 µg per Kg, i. v.) in man and rabbit. In such circumstances, the sensitivity
of platelets to aggregation induced by ADP was studied by an optical density method.
Five minutes after i. v. injection of 1 µg per Kg of adrenaline in 10 rabbits, intensity
of platelet aggregation increased to 115.1 ± 4.9% (mean ± S. E.) by 10∼5 molar, 121.8 ± 7.8% by 3 × 10-6 molar and 129.4 ± 12.8% of the value before the injection by 10”6 molar ADP. The difference was statistically significant (P<0.01-0.05). The above
change was not observed in each group of rabbits injected with saline, 1 µg per Kg
of 1-noradrenaline or 0.1 and 10 µg per Kg of adrenaline. Also, it was prevented by
oral administration of 10 mg per Kg of phenoxybenzamine or propranolol or aspirin
or pyridinolcarbamate 3 hours before the challenge. On the other hand, the enhancement
of ADP-induced platelet aggregation was not observed in vitro, when 10-5 or 3 × 10-6 molar and 129.4 ± 12.8% of the value before 10∼6 molar ADP was added to citrated platelet rich plasma (CPRP) of rabbit after incubation
at 37°C for 30 second with 0.01, 0.1, 1, 10 or 100 µg per ml of adrenaline or noradrenaline.
These results suggest an important interaction between endothelial surface and platelets
in connection with the enhancement of ADP-induced platelet aggregation by adrenaline
in vivo.
