Osmoreceptors or sodium receptors: an investigation into ADH release in the rhesus monkey.

1. ADH secretion was studied in trained, preoperated conscious monkeys undergoing water diuresis after administration of isosmolar hypertonic solutions of different substances into any one of the following sites: (i) anterior third ventricle, (ii) the hypothalamus, just anterior to the third ventricle and (iii) common carotid artery. 2. Free water clearance was continuously monitored and the ADH released was measured by bio-assay on the same animals after administering graded doses of standard arginine vasopressin in a comparable manner. 3. Intraventricular infusions of hypertonic solutions of NaCl or Na acetate released significant amounts of ADH while sucrose or mannitol of comparable osmolality were ineffective. Graded increases in the concentration of NaCl infused into the c.s.f. resulted in secretion of ADH proportional to log Na concentration. 4. Infusion of the same hypertonic solutions into the anterior hypothalamus released ADH, though Na salts were more effective than the sugars. 5. Hypertonic solutions of NaCl, Na acetate, sucrose or mannitol were effective in releasing ADH when injected via the carotid artery, but hypertonic solutions of NaCl were significantly more effective than the other solutions. 6. These findings may be explained by the hypothesis that the 'osmoreceptors' of Verney are Na sensitive receptors composed of dendrites innervating the specialized ependyma of the anterior part of the third ventricle.