CHARACTERIZATION OF ALPHA(2)-ADRENOCEPTOR SUBTYPES IN PREGNANT HUMAN MYOMETRIUM

The aim of the present investigation was to determine which subtypes o f the alpha(2)-adrenoceptors are being expressed in the human pregnant myometrium at term pregnancy. In radioligand binding studies, the spe cific binding of [H-3]rauwolscine to human myometrial membranes was sp ecific and of high affinity with K-d of 2.8 +/- 0.6nM and B-max of 95 +/- 5 fmol/mg protein. Results from competition for the binding of [H- 3]rauwolscine using subtype-selective ligands, oxymetazoline (alpha(2) A-subptype), chlorpromazine (alpha(2)B-subtype) and prazosin (alpha(2) B-alpha(2)C-subtype), suggested that the alpha(2)A- and alpha(2)B-subt ypes are being co-expressed. In order to examine if also the alpha(2)C -subtype is being expressed we used an optimal concentration of oxymet azoline or chlorpromazine which would block the high-affinity site, eq uivalent to the alpha(2)A- and alpha(2)B-subtype respectively. Competi tion curves of both oxymetazoline and chlorpromazine still showed a si gnificantly better fit using a two-site model, suggesting that the alp ha(2)C-subtype also is being expressed. The expression of alpha(2)C-su btype 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 alpha(2)-adrenoceptors are being coexpressed in the human myometrium at term pregnancy and that alpha(2)-expression is dominated by the alpha(2)A-subtype.