Presence of D2-dopamine receptors in human term placenta.
We studied the binding of [3H]-spiperone on human term placental membranes. This binding reached plateau level after 30 min incubation at 37 degrees C and was reversed (t1/2 approximately 5 min) by addition of an excess of unlabeled spiperone. Scatchard analysis of saturation experiments with increasing doses of [3H]-spiperone (0-25 nM) showed one class of high affinity binding sites with a dissociation constant (Kd) of 14 +/- 2 nM and a maximal binding capacity (Bmax) of 222 +/- 9 fmoles/mg protein. The affinity of 5 competitors was determined in competitive binding assays. The D2-dopamine antagonists were the most potent inhibitors: Ki for spiperone and haloperidol were 8 +/- 2 and 56 +/- 22 nM respectively. Dopamine inhibited [3H]-spiperone binding with a Ki of 570 +/- 50 microM whereas Schering 23390 (D1 antagonist) and propranolol (beta-adrenergic antagonist) were without effect. The binding was also inhibited by 100 microM GTP gamma S (38 +/- 8% inhibition), indicating that the dopamine receptor is coupled with a GTP binding protein. These results demonstrate for the first time the presence of D2-dopamine receptors in human placenta.
Petit
A
A
Department of Biochemistry, Faculty of Medicine, University of Sherbrooke, Québec, Canada.
Vaillancourt
C
C
Bellabarba
D
D
Lehoux
J G
JG
Gallo-Payet
N
N
Bélisle
S
S
D004298:Dopamine / Q000502:physiology; D005260:Female; D006801:Humans; D007743:Labor, Obstetric / Q000502:physiology; D010920:Placenta / Q000737:chemistry*; D011247:Pregnancy; D011388:Prolactin / Q000378:metabolism; D011954:Receptors, Dopamine / Q000032:analysis*; D017448:Receptors, Dopamine D2; D013134:Spiperone / Q000378:metabolism
D011954:Receptors, Dopamine; D017448:Receptors, Dopamine D2; D013134:Spiperone; D011388:Prolactin; D004298:Dopamine