To elucidate the modulatory role of the brain renln-angiotensin system in the regulation of the secretion of atrial natriuretic factor (ANF) from the heart, the effects of intracerebroventricular administration of angiotensin II on the plasma ANF level were examined in conscious unrestrained rats. Administration of angiotensin II in doses of 100 ng and 1 fig significantly enhanced ANF secretion induced by volume loading with infusion of 3 ml of saline (peak values of the plasma ANF level: control, 220 ± 57 pg/ml; angiotensin II 100 ng, 1110 ± 320 pg/ml, p < 0.01; angiotensin II 1μg, 1055 ± 60 pg/ml, p < 0.01). Injection of angiotensin II alone had no significant effect on the basal plasma ANF level. Central angiotensin H-induced ANF secretion was significantly attenuated by pretreatment with intravenous administration of the V1-receptor antagonist of vasopressin or intracerebroventricular administration of phentolamine. These results indicate that the brain renln-angiotensin system modulates ANF secretion in response to volume loading through the stimulation of vasopressin secretion or the activation of the central α-adrenergic neural pathway.
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