Adrenaline and Experimental Thrombosis*

T he acceleration of blood coagulation in vivo by adrenaline was first demonstrated by Vosburgh and Richards in 1903. They showed in man that adrenaline in doses of 7 μg. per kg. body weight shortened the coagulation time by about 50 per cent. Subsequent studies led to conflicting conclusions until the experiments of Cannon and Gray in 1914, who showed that small doses of adrenaline promoted coagulation, but that larger doses inhibited it. This was confirmed by later investigators (Waldron, 1951; Forwell and Ingram, 1957) but, so far as we know, the effect in normal animals of adrenaline on thrombus formation, as distinct from coagulation, has not been explored. More recently, evidence has been presented that adrenaline increases Factor‐VIII activity (Ingram, 1961), shortens platelet survival and increases platelet turnover (Adelson, Rheingold, Parker, Buenaventura and Crosby, 1961; Özge and Mustard, 1964). Recently, Mitchell and Sharp (1964) and O'Brien (1963) have shown that adrenaline promotes platelet aggregation in vitro. In the present study we have directed our attention to the effect of this drug on blood coagulation, platelets and thrombus formation. Quantitative study of thrombus formation has been made possible by the development of a standard extracorporeal circulation which allows precise measurement (Downie, Murphy, Rowsell and Mustard, 1963). In view of the findings of earlier investigators studying coagulation, it seemed important to determine how dosage levels affect the results.