Postjunctional alpha 1- and alpha 2-adrenoceptors in cat forepaw vasculature

Preganglionic stimulation of the thoracic sympathetic nerve trunk produced frequency-related decreases of ulnar arterial blood flow in the forepaw of anesthetized cats as measured by ultrasonic flowmetry. Vasoconstrictor responses were not altered by administration of propranolol or atropine. When given alone, both prazosin (3-100 micrograms/kg, i.v.) and rauwolscine (10-300 micrograms/kg, i.v.) produced only a modest reduction of sympathetic evoked vasoconstriction. However, extensive blockade was obtained when both antagonists were administered to the same animal. These results suggest that both alpha 1- and alpha 2-adrenoceptors coexist at postsynaptic sites in the vasculature of the cat paw and that neural activation of either type results in potent vasoconstriction.