THE EFFECT OF CHOLINOCEPTOR AGONISTS AND NEUROTOXINS ON THE RELEASE OF VASOPRESSIN IN THE RAT IN RELATION TO THE SUBUNIT COMPOSITION OF THECHOLINOCEPTOR

The effects of cholinoceptor agonists and neurotoxins on the release o f vasopressin and oxytocin have been investigated in water-loaded rats under ethanol anaesthesia. Release of vasopressin was monitored by an tidiuretic responses accompanied by increased urinary excretion of vas opressin. The rate of excretion of oxytocin-like radioimmunoreactivity was measured as an indicator of oxytocin release. Both nicotine and c ytisine caused a preferential release of vasopressin. The release by n icotine was not inhibited by alpha- or neuronal-bungarotoxin. Neosurug atoxin blocked the release by cytisine. Comparison with the effects of these agents on combinations of alpha and beta subunits expressed in oocytes suggests that the central cholinoceptors mediating release of vasopressin are similar to those at autonomic ganglia and may contain a beta 4 subunit.