A comparison of guanfacine, bunazosin, atenolol and nadolol on blood pressure and plasma noradrenaline responses to cold pressor testing.

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1. The role of the presynaptic adrenoceptor subtypes in man was investigated based on observation of the changes in blood pressure (delta BP) and plasma noradrenaline concentration (delta NA) with the cold pressor test (CPT). 2. The CPT was well reproducible for BP and NA when performed at a 2 week interval in patients with mild hypertension. 3. After administration for 4 weeks, guanfacine (Gf; alpha 2-adrenoceptor agonist) decreased the delta NA response to CPT. 4. After administration for 2 or 4 weeks, bunazosin (Bu; alpha 1-adrenoceptor antagonist) atenolol (At; beta 1-adrenoceptor antagonist) and nadolol (Nd; non-selective beta-adrenoceptor antagonist) did not affect the delta NA response to CPT. 5. Both Gf and Bu decreased the systolic blood pressure response (delta SBP) to CPT after 4 weeks of the administration. Neither At nor Nd significantly changed the delta SBP response to CPT. 6. It is likely that Gf stimulated the presynaptic alpha 2 adrenoceptors at the sympathetic nerve endings as well as the central alpha 2 adrenoceptors, inhibiting the release of noradrenaline. It is unlikely that Bu, At and Nd exerted any clearly defined action on the presynaptic adrenoceptors in human hypertensive subjects.