1. Six male beagle dogs with carotid loops were infused with sodium chloride solution (150 mmol/l: saline) during control observations followed by dopamine infusion at various rates. Arterial blood samples were drawn during the control period and at the end of each period of dopamine infusion for the measurement of plasma dopamine, noradrenaline, adrenaline, renin, angiotensin II, aldosterone, vasopressin, electrolytes and packed cell volume. Blood pressure and pulse were recorded throughout.

2. The rate of infusion and plasma dopamine levels were closely correlated (r = 0.99, P < 0.001). Plasma dopamine levels two to 20 times basal values produced no significant change in any of the other variables measured; levels 200 times basal values caused a significant increase (P < 0.05) in plasma renin concentration; levels 2000 times basal values were associated with significant increases (P < 0.05) in plasma renin and angiotensin II, packed cell volume and blood pressure, without significant changes in other measurements.

3. Circulating dopamine is unlikely to be important in the control of sodium and water metabolism.

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