“…This difference has also been observed with the irreversible x-adrenoceptor blocking drug, phenoxybenzamine. Phenoxybenzamine was 100 times more potent than phentolamine as a postsynaptic a-adrenoceptor blocking drug in the cat isolated spleen and ten times more potent as a presynaptic x-adrenoceptor blocking drug in the cat spleen (Cubeddu, Barnes, Langer & Weiner, 1974) and the rabbit isolated heart (Starke, Montel & Schumann, 1971;Starke, Montel &--Wagner, 1971) and had a very low potency inhuman platelets (Clayton & Cross, 1963;O'Brien, 1963;1964;Bygdeman & Johnsen, 1969;Jakobs, Saur & Schultz, 1978;Lasch & Jakobs, 1979) or was inactive (Born, Mills & Roberts, 1967;Mills & Roberts, 1967a;Hsu, Knapp & Halushka, 1979). Compared to phentolamine, phenoxybenzamine had a higher affinity for both postsynaptic and presynaptic aadrenoceptors but a much lower affinity for platelet o-adrenoceptors.…”