alpha-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 alpha-flupenthixol. This inhibition was slow in onset (60 min) and in reversal (greater than 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 (less than 3 microM) 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 alpha-flupenthixol. 5 beta-Flupenthixol was shown to antagonize responses to dopamine; however it was 10 to 100 times less potent than alpha-flupenthixol.