Role of catecholamine release in cardiovascular responses to angiotensin

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Abstract
The effects of intravenous angiotensin on cardiac output, arterial pressure, peripheral resistance, and inferior and superior vena cavalf lows were studied in the cat. Two phases of the response were distinguished. In the first, arterialpressure rose, cardiac outputfell or remained unchanged, peripheral resistance increased, superior vena caval flow increased, an inferior vena cavalf low decreased. In the second stage the pressor response transiently diminished, cardiac output andf low inthe venae cavae increased while peripheral resistance decreased. After adrenalectomy the first stage responses were not materially altered, but the second-stage increases in cardiac output and vena caval flows were considerably diminished, whereas the fall in peripheral resistance was less pronounced. After beta adrenergic blockade, cardiac output fell during the first stage and remained low in the second. Arterial pressure and peripheral resistance fell to a lesser extent during the second stage. The results indicate that catecholamines liberated from the adrenal medulla and sympathetic nerve endings play an important role in the cardiovascular responses to angiotensin.