α‐FLUPENTHIXOL: AN ANTAGONIST OF DOPAMINE‐EVOKED FLUID SECRETION BY AN INSECT SALIVARY GLAND PREPARATION

1 We have demonstrated inhibition of secretory responses of cockroach salivary glands to dopamine, adrenaline, noradrenaline and neurotransmitter by α‐flupenthixol. This inhibition was slow in onset (60 min) and in reversal (> 2 h). 2 Inhibition of responses to adrenaline and noradrenaline was non‐competitive, since the maxima and slopes of dose‐response curves of these agonists were reduced. 3 Although at low concentrations (< 3 μm) the antagonism of responses to dopamine showed some characteristics of competitive inhibition, at higher doses non‐competitive inhibition was clearly demonstrated. 4 These results are explained in terms of different efficacies of the agonists for the receptors antagonized by α‐flupenthixol. 5 β‐Flupenthixol was shown to antagonize responses to dopamine; however it was 10 to 100 times less potent than α‐flupenthixol.