Absence of muscarinic modulation of vasopressin release from the isolated rat neurohypophysis

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Abstract
Isolated rat neurohypophyses were incubated in Locke solution at 37°C and the vasopressin output into the medium determined by bioassay. Potassium chloride 60 mM caused a 9-fold increase in the rate of vasopressin release that was abolished when calcium chloride was omitted from the Locke solution. Acetylcholine 5.5×10−4 M neither alone nor in the presence of atropine 2.9×10−6 M changed the “resting” release of vasopressin. Neither acetylcholine 5.5×10−4 M nor oxotremorine 10−4 and 3×10−4 M altered the vasopressin release evoked by potassium chloride 60 mM. In contrast to the peripheral adrenergic nerve fibres, the secretory terminal fibres of the neurohypophysis do not appear to contain muscarinic inhibitory or nicotinic excitatory receptors.