Cholinergic Involvement in Osmotic Control of Vasopressin Release by the Organ-Cultured Rat Hypothalamo-Neurohypophyseal System*

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Abstract
A nicotinic-cholinergic receptor appears to mediate osmotic stimulation of vasopressin (VP) release by the hypothalamo-neurohypophyseal explant. Nicotinic blocking agents, hexamethonium, tetraethylammonium chloride, and trimethaphan, blocked VP release in response to the addition of sufficient NaCl to yield a 10 mosm/kg H2O increase in culture medium osmolality. Atropine at a similar molar concentration was ineffective in blocking VP release in response to the same osmotic stimulus. Tetraethylammonium chloride and trimethaphan also blocked acetylcholine-stimulated VP release. These findings support the hypothesis that the osmoreceptive element responsible for controlling VP release resides in a separate cell and communicates with the VP cell by way of a nicotiniccholinergic receptor.