ACTIONS OF LOCALLY ADMINISTERED ADRENOCEPTOR AGONISTS ON INCREASED PLASMA PROTEIN EXTRAVASATION AND BLOOD FLOW IN GUINEA‐PIG SKIN

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Abstract
Bradykinin‐induced increased plasma protein extravasation (IPPE) and blood flow have been assessed in guinea‐pig skin by isotopic methods. The effects of a range of adrenoceptor agonists on these parameters have been investigated. α‐Adrenoceptor agonists inhibited IPPE and reduced cutaneous blood flow. The potency of α‐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. β‐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. The inhibitory action of α‐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.