Presence of dopamine DA-1 receptors in human decidua

To evaluate the role of dopamine in human parturition, we studied the presence of dopamine receptors in human decidua obtained immediately after delivery, using a radiolabelled receptor assay. [3H]SCH23390, a dopamine DA-1 receptor ligand was used to identify and characterize the DA-1 receptor. Scatchard analysis of our saturation experiments revealed one class of high-affinity binding sites. The equilibrium dissociation constant (Kd) for binding of [3H]SCH23390 to decidual DA-1 receptors was 1.87 +/- 0.16 nM (mean +/- s.d. n = 3) at 30 degrees C. The maximum binding capacity (Bmax) was 79.0 +/- 15.4 fmol/mg protein at 30 degrees C. The specificity of DA-1 receptor binding was inhibited by SCH23390 (a DA-1 antagonist), SKF38393 (a DA-1 agonist) and dopamine with the inhibitory constants (Ki) of 5.82 +/- 2.27 nM (mean +/- s.d., n = 3), 45.6 +/- 30.5 nM (mean +/- s.d. n = 3) and 2.86 +/- 1.02 microM (mean +/- s.d., n = 3) respectively. However, (+/-)-sulpiride (a DA-2 antagonist) and (-)-propranolol (a beta-adrenergic antagonist) were without effect. The specific binding of [3H]spiperone (a DA-2 receptor ligand) was not detected. We previously reported that in vitro the human decidual tissues produce significant amounts of prostaglandins in the presence of dopamine. We postulate that dopamine regulates the production of prostaglandin in human decidua via DA-1 receptors.