The purpose of this study was to examine the effects of atrial natriuretic peptide (ANP) on the secretion of vasopressin and the activities of hypothalamic tuberohypophysial and tuberoinfundibular dopaminergic neurons in normal and dehydrated male rats. Neuronal activity was estimated by measuring the concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) and dopamine (DA) in brain and posterior pituitary regions containing terminals of tuberohypophysial (neural lobe; intermediate lobe) and tuberoinfundibular (median eminence) DA neurons. Intracerebroventricular (icv) administration of 20 micrograms ANP decreased basal arginine vasopressin concentrations in the plasma, but had no effect on the concentrations of DOPAC or DA in any region examined. Water deprivation caused a time-dependent increase in plasma arginine vasopressin concentrations, with maximal levels measured 2 days after removal of water bottles. Water deprivation had no effect on DOPAC concentrations in the neural lobe, intermediate lobe or median eminence, but increased DA concentrations in the neural lobe. ANP (20 micrograms/rat; icv) decreased arginine vasopressin concentrations in the plasma of water-deprived rats without altering DOPAC or DA concentrations in the neural lobe, intermediate lobe or median eminence. These results indicate that ANP-induced suppression of basal and dehydration-induced vasopressin secretion is not mediated by tuberohypophysial or tuberoinfundibular DA neurons.