IDENTIFICATION OF THE MESSENGER-RNA FOR THE NOVEL ALPHA(1D)-ADRENOCEPTOR AND 2 OTHER ALPHA(1)-ADRENOCEPTORS IN VASCULAR SMOOTH-MUSCLE

In situ hybridization histochemistry, radioligand binding, and in vitr o contractile studies were used to characterize the vascular distribut ion of the recently discovered alpha(1D)-adrenoceptor. In situ hybridi zation with an antisense probe localized the mRNA for the alpha(1D)-ad renoceptor to the medial layer of the rat aorta renal and mesenteric r esistance arteries. If the tissues were first treated with RNase or a sense probe was used, no specific hybridization signal was detected. T he extent to which this receptor was expressed as protein was assessed with radioligand binding studies. A series of ligands used to charact erize alpha(1)-adrenoceptors interacted with two sites labeled by [H-3 ]prazosin in homogenates from the aorta and mesenteric vascular bed. T he high affinity site had the characteristics of an alpha(1A)-adrenoce ptor. However, the low affinity site had ligand binding characteristic s distinct from those of the alpha(1D)-adrenoceptor or any other known alpha(1)-adrenoceptor subtype. mRNA for the alpha(1B)- and alpha(1C)- adrenoceptors was also detected in the aorta, renal arteries, and mese nteric resistance arteries. Chloroethylclonidine (CEC)(1 and 10 mu M) had differential effects on phenylephrine-induced contractions of vasc ular smooth muscle. CEC completely inhibited the response in the aorta and caused a partial inhibition in the mesenteric resistance artery. The same concentrations of CEC had little effect on phenylephrine resp onses in the renal artery. The data suggest the following. 1) mRNA for the novel alpha(1D)-adrenoceptor is localized in vascular smooth musc le. 2) Definitive identification of expression of this receptor was no t possible; this may be related to coexpression of other subtypes of a lpha(1)-adrenoceptors. 3) mRNA for the alpha(1C)-adrenaceptor was dete cted in rat peripheral vasculature. 4) The alpha(1A)-adrenoceptor is a lso localized in the vasculature. 5) Three and possibly four alpha(1)- adrenoceptors participate in vascular smooth muscle regulation.