The effect of reserpine on the pressor responses to angiotensin in the conscious cat.

1. Blood pressure recordings have been made in conscious cats in an attempt to reveal a possible indirect component to the angiotensin pressor response.2. Reserpine (50 to 250 mug/kg per day) caused a maximal reduction of about 50% in the pressor response to angiotensin whilst virtually abolishing the responses to tyramine and McN-A-343. Responses to noradrenaline were only slightly and transiently reduced.3. Syrosingopine (0.5 mg/kg) and reserpine (250 mug/kg) reduced the responses to angiotensin, McN-A-343 and tyramine to much the same extent, but tetrabenazine only reduced the responses to all these agents in a dose (25 mg/kg) which probably had effects on the catecholamine stores of smooth muscle.4. The reduction in the responses to angiotensin, tyramine and McN-A-343 by reserpine was partly reversed by tranylcypromine. Noradrenaline and (+/-)-dopa infusions were ineffective by themselves, but increased the effects of tranylcypromine in restoring the responses to angiotensin, tyramine and McN-A-343 after reserpine.5. Infusion of alpha-methyldopa markedly increased the responses to angiotensin, tyramine and McN-A-343 after these had been reduced by reserpine.6. The results suggest that the pressor response to angiotensin in the conscious cat is partly mediated by release of noradrenaline from peripheral neuronal stores.