Arterial pressure responses to adrenoceptor antagonism in rats with sino-aortic deafferentation.

1. The effect of sequential alpha and beta adrenoceptor blockade on mean arterial pressure (MAP) and arterial pressure lability (APL) was studied 3 and 15 days after sino-aortic deafferentation (SAD) in rats. 2. Prazosin, an alpha-1 adrenoceptor blocker, injected iv (1 mg/kg) into SAD rats 3 days after surgery produced a significant fall in MAP (-61 vs -21 mmHg) and APL (-7 vs 0 mmHg) when compared with sham-operated rats. 3. Propranolol, a beta-1 and -2 adrenoceptor blocker, injected iv (1 mg/kg) after prazosin into SAD rats (3 days) produced a significant increase in MAP (+37 vs +5 mmHg) and APL (+4 vs 0 mmHg) when compared with sham-operated rats. 4. Prazosin injected iv (1 mg/kg) into SAD rats 15 days after surgery produced smaller changes in MAP than observed in rats 3 days after SAD but a significant fall in MAP (-35 vs -13 mmHg) when compared with sham-operated rats. At this phase of SAD, no changes in APL were observed after prazosin. 5. Propranolol injected iv (1 mg/kg) after prazosin into SAD and sham-operated rats (15 days) produced no changes in MAP and APL. 6. Prazosin injected into SAD rats (3 and 15 days) with previous adrenal demedullation produced falls in MAP and APL similar to those observed in SAD rats with intact adrenals. 7. In contrast to SAD rats with intact adrenals, propranolol injected after prazosin into SAD rats (3 days) with previous adrenal demedullation produced no increase in MAP. 8. These results suggest that a) alpha-1 adrenoceptors are directly involved in MAP maintenance in SAD rats 3 and 15 days after surgery; b) 2 weeks after SAD, compensatory reflex mechanisms may be acting to reduce the fall in MAP produced by prazosin; c) alpha-1 adrenoceptors are not directly involved in APL generation; d) APL is related to the activation of beta adrenoceptors by endogenous epinephrine release.