Hypothalamic integration of dopaminergic and opiate pathways controlling vasopressin secretion

Lesions of the circumventricular organs were produced by administration of monosodium-L-glutamate to neonatal rats. At 16 weeks of age these rats were given different stimuli to vasopressin release. In control rats, morphine (50 micrograms) injected into the third ventricle resulted in a rapid increase in plasma vasopressin concentrations at 10 min, followed by a reduction at 20 min. The circumventricular organ-lesioned rats, however, showed a pronounced fall in vasopressin secretion both at 10 and 20 min after 50 micrograms morphine. A similar abolition of the morphine-elicited rise in plasma vasopressin could also be achieved by the iv infusion of small doses of dopamine in normal rats. Hypoxic stimuli, which result in a marked rise in vasopressin in normal rats, failed to elicit any increase in circumventricular organ-lesioned animals. Vasopressin release after stimulation with 9% saline, however, was augmented in the lesioned animals. These results suggest that circumventricular organs have an important role in controlling neurohypophyseal secretion and that they differentially control different stimuli to vasopressin release via dopaminergic and opiate pathways.