Alpha-1 adrenergic receptor: binding and phosphoinositide breakdown in human myometrium.
Alpha-1 adrenergic receptors were examined in both inner and outer layers of human pregnant myometrium using radioligand binding of [3H]prazosin. [3H]prazosin bound rapidly and reversibly to a single class of high affinity binding sites in myometrial membrane preparations. Scatchard analysis gave similar values of equilibrium dissociation constants in both myometrial layers. In contrast, more alpha-1 adrenergic receptors were detected in the outer layer than in the inner layer. Antagonist inhibited [3H]prazosin binding with an order of potency of prazosin greater than phentolamine greater than idazoxan. Competition experiments have also revealed that a stable guanine nucleotide decreases the apparent affinity of norepinephrine for myometrial [3H]prazosin binding sites. The functional status of these alpha-1 adrenergic receptors was also assessed by measuring the norepinephrine-induced accumulation of inositol phosphates in myometrial tissue. Norepinephrine produced a concentration-dependent accumulation of inositol phosphates in both myometrial layers. However, norepinephrine-induced increases in inositol 1,4,5-triphosphate were only observed in the outer layer. These results indicate that alpha-1 adrenergic receptors in human myometrium at the end of pregnancy are linked to phosphoinositide hydrolysis and that this response occurs mainly in the outer layer.
Breuiller-Fouche
M
M
INSERM U.166 Groupe de recherches sur l'Endocrinologie de la Reproduction, Maternité Baudelocque, Paris, France.
Doualla-Bell Kotto Maka
F
F
Geny
B
B
Ferre
F
F
D001667:Binding, Competitive; D005260:Female; D006801:Humans; D007700:Kinetics; D009215:Myometrium / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism*; D011224:Prazosin / Q000378:metabolism*; D011247:Pregnancy; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D014316:Tritium
D010716:Phosphatidylinositols; D011942:Receptors, Adrenergic, alpha; D014316:Tritium; D009638:Norepinephrine; D011224:Prazosin