Fig. 6. The effect of D1-selective antagonists on dopamine-stimulated cAMP production in the albumen gland of H. duryi. All agents were used at a concentration of 10 µmol l^-1 and applied to the glands for 10 min. For the dopamine plus antagonist combinations, the glands were first pre-incubated in antagonist for 20 min.Dopamine (DA) significantly increased cAMP levels in the albumen glands compared with untreated control glands (CON). (A) The D1-selective antagonist SCH23390 had no effect on basal cAMP levels but significantly inhibited dopamine-stimulated cAMP production (^*P<0.001, Tukey test). (B) The D1-selective antagonist SKF83566 significantly suppressed dopamine-stimulated cAMP production and had no effect on basal cAMP levels (^*P<0.001, Tukey test). (C) By contrast, flupenthixol (FLU), another D1-selective antagonist, did not cause a statistically significant suppression of dopamine-stimulated cAMP production (^*P<0.05, Tukey test). All agents were used at a concentration of 10 µmol l^-1. Bars represent the mean ± S.E.M. of 5–6 samples.