Fig. 4. The effect of dopamine and various D1-selective agonists on albumen gland cAMP production. Albumen glands were quartered and treated with either dopamine, a D1-selective agonist or dopamine + agonist. (A) Dopamine (DA) caused a significant elevation of albumen gland cAMP levels when compared with untreated control glands (CON), whereas dihydrexidine (DH) caused a modest but statistically significant elevation of albumen gland cAMP levels. Application of dopamine and dihydrexidine together was unable to elevate cAMP levels above those of dopamine-treated glands (^*P<0.05, ^**P<0.001, Tukey test). (B) The non-selective dopamine receptor agonist 6,7-ADTN was equally as potent as dopamine on albumen gland cAMP production (^*P<0.05, Tukey test). (C) The partial D1-selective agonist SKF81297 (SKF) induced a modest elevation above basal cAMP production in the albumen gland but it was not statistically significant when compared with control glands (^*P<0.001, 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.