Actions of locally administered adrenoceptor agonists on increased plasma protein extravasation and blood flow in guinea-pig skin.

1 Bradykinin-induced increased plasma protein extravasation (IPPE) and blood flow have been assessed in guinea-pig skin by isotopic methods. 2 alpha-Adrenoceptor agonists inhibited IPPE and reduced cutaneous blood flow. The potency of alpha-agonists as inhibitors of IPPE correlated with their vasoconstrictor effects. The actions of noradrenaline on both IPPE and blood flow were blocked by phentolamine but not by propranolol. 4 beta-Adrenoceptor agonists inhibited IPPE at doses which either increased or caused little change in cutaneous blood flow. Isoprenaline inhibition of IPPE was reduced by propranolol but was unaffected by phentolamine. 5 The inhibitory action of alpha-agonists on IPPE can be explained by a reduction in blood flow to the affected site. Beta agonist inhibition is not due to effects on blood flow but is probably caused by a reduction in permeability of the microvessels.