Diuretic Effect of Intraventricular and Intravenous Infusions of Noradrenaline in Conscious Sheep

Influsion of noradrenaline at rates between 32 160 nmol.min ‐1 for 30 min into one lateral cerebra; ventricle of conscious sheep caused a diuresis which was accompanied by negative solute‐free water reabsorption and which lasted for 90 120 min. The range of noradrenaline infusion rates used reflects differences between individual animals in the rate of infusion necessary to cause diuresis. Intracerebroventricular (ICV) infusion of noradrenaline at half the diuretic rate caused no significant changes in urine flow. The diuresis induced by ICV noradrenaline infusion was prevented by concurrent ICV administration of the α‐adrenergic analgonist, phentolamine, but was not prevented by concurrent ICV administration of the β antagonist, propranolo, or by concurrent intravenous infusion of phentolamine. Intravenous infusion of naradrenaline at rates that were diuretic by ICV infusion caused a diuresis of approximately 30 min duration which coincided with the period of intravenous noradrenaline infusion. This diuresis was prevented by concurrent intravenous infusion of phentolamine. These results were interpreted as indicating that the higher rates of ICV infusion of noradrenaline caused the prolonged water diuresis by acting at a site in the brain and, thereby, inhibiting the release of endogenous vasopressin. ICV infusion of noradrenaline at all rates was followved by a reduction in mean arterial blood pressure and pulse pressure with variable changes in heart rate and by drepression of the rates of renal clearance of PAH. potassium and total solute.