title: Adrenaline induces vasoconstriction through post-junctional alpha 2 adrenoceptors and this response is enhanced in patients with essential hypertension.
abstract: The role of adrenaline-induced postjunctional alpha 2 adrenoceptor-mediated vasoconstriction was studied in seven patients with essential hypertension (EHT) and eight normotensive subjects (NT) using forearm venous occlusion plethysmography. Adrenaline (0.01 to 0.08 micrograms/min/100 ml of tissue) infused into the forearm circulation via the brachial artery during alpha l adrenoceptor blockade with prazosin (0.05 micrograms/min/100 ml of tissue) and beta adrenoceptor blockade with propranolol (2 micrograms/min/100 ml of tissue) decreased forearm blood flow (FAF) dose-dependently below basal FAF (P less than 0.001). The adrenaline-induced decrease in FAF was greater in EHT than in NT (P less than 0.01) and was blocked in both groups by alpha 2 adrenoceptor blockade with yohimbine (30 micrograms/min/100 ml of tissue). The increase in FAF following postjunctional alpha-2 blockade as well as following postjunctional alpha-1 blockade was greater in EHT than in NT (P less than 0.01) but was similar in both groups following 'non-specific' vasodilation with sodium nitroprusside. Postjunctional alpha 1 and alpha 2 adrenoceptor-mediated vasoconstriction is enhanced in patients with essential hypertension. Adrenaline induced postjunctional alpha 2 adrenoceptor-mediated vasoconstriction could contribute to elevated vascular resistance in patients with EHT and elevated plasma adrenaline concentrations particularly in the presence of blunted beta adrenoceptor-mediated functions.
mesh_terms: D000328:Adult; D004837:Epinephrine / Q000494:pharmacology*; D005260:Female; D005542:Forearm / Q000098:blood supply; D006801:Humans; D006973:Hypertension / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009599:Nitroprusside / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D012039:Regional Blood Flow / Q000187:drug effects; D014661:Vasoconstriction / Q000187:drug effects*; D014664:Vasodilation / Q000187:drug effects; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D011942:Receptors, Adrenergic, alpha; D009599:Nitroprusside; D015016:Yohimbine; D011433:Propranolol; D011224:Prazosin; D004837:Epinephrine