Characterization of α2-Adrenoceptor Subtypes in Pregnant Human Myometrium

• The aim of the present investigation was to determine which subtypes of the α2-adrenoceptors are being expressed in the human pregnant myometrium at term pregnancy. In radioligand binding studies, the specific binding of [3H]rauwolscine to human myometrial membranes was specific and of high affinity with Kd of 2.8 ± 0.6 nM and Bmax of 95 ± 5 fmol/mg protein. Results from competition for the binding of [3H]rauwolscine using subtype-selective ligands, oxymetazoline (α2A-subptype), chlorpromazine (α2B-subtype) and prazosin (α2B-α2C-subtype), suggested that the α2A- and α2B-subtypes are being co-expressed. In order to examine if also the α2C-subtype is being expressed we used an optimal concentration of oxymetazoline or chlorpromazine which would block the high-affinity site, equivalent to the α2A- and α2B-subtype respectively. Competition curves of both oxymetazoline and chlorpromazine still showed a significantly better fit using a two-site model, suggesting that the α2C-subtype also is being expressed. The expression of α2C-subtype mRNA was confirmed using reverse transcription-polymerase chain reaction on mRNA isolated from myometrial biopsies.In conclusion, our results suggest that all three subtypes of α2-adrenoceptors are being coexpressed in the human myometrium at term pregnancy and that α2-expression is dominated by the α2A-subtype.

Nyckelord

α2-Adrenergic receptors

Subtype

Myometrium

Human

Pregnancy

[3H]rauwolscine

Reverse transcription-polymerase chain reaction

MEDICINE

MEDICIN

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