Effect of intracerebroventricular administration of dopamine on urinary function in goats

Dopamine (DA) and several blocking substances were administered into the 3rd ventricle of conscious goats to study the effects on water and electrolyte excretion. Intracerebroventricular infusion of DA in hydrated goats induced a significant dose-dependent inhibition of both the urine flow rate and the renal free water clearance. A biphasic response pattern of urinary electrolyte excretion, consisting of an initial fall, followed by an increase in the excretion rate was observed. The antidiuretic effects induced by DA could be prevented by prior administration of haloperidol, pimozide or phentolamine into the 3rd ventricle. Atropine, hexamethonium or propranolol were ineffective. It seems that excitatory responses of periventricular neurons resulting in vasopressin release in the goat may be mediated by both alpha-adrenoceptors and excitatory DA receptors. Furthermore, single injection of haloperidol or pimozide into the 3rd ventricle of goats with a normal water balance induced both a significant diuretic response and an increase in renal free water clearance. The data suggest that endogenous DA in the hypothalamus could be responsible for vasopressin release.