Effect of transection of subfornical organ efferent projections on vasopressin release induced by angiotensin or isoprenaline in the rat

Transection of subfornical organ efferents in the rat prevented the vasopressin release in response to intravenous angiotensin II infusion or following a small dose of the β-sympathomimetic amine isoprenaline (30 μ/kg i.m.). In contrast, this lesion had no effect on vasopressin release after hypertonic saline injection or a high dose of isoprenaline (480 μg/kg i.m.). We conclude that blood-borne angiotensin II induces vasopressin release by acting on the subfornical organ; depending on the dose of isoprenaline, activation of the endogenous renin-angiotensin system may mediate isoprenaline-induced vasopressin release.