Presence of beta- but not alpha-adrenoceptors in the rat jugular vein: autoradiographical evidence.

ABSTRACT

Previous functional studies with the rat jugular vein have shown alpha-adrenergically mediated contraction was minimal to nonexistent, yet this tissue relaxed in response to norepinephrine via beta 1 and to isoproterenol via beta 2-receptor activation. Unlike the rat jugular vein, the rat aorta markedly contracted to norepinephrine and relaxed to beta-adrenoceptor stimulation. This study qualitatively examined the alpha- and beta-receptor distributions in the rat jugular vein, as compared to the rat aorta, with autoradiographical methods. Cross-sections of blood vessels were labelled with the alpha-receptor ligand, [125I]HEAT ([beta-(4-hydroxy-3-iodophenyl)-ethyl-aminomethyl]-tetralone) and the beta-receptor ligand, [125I]ICYP (iodo-cyanopindolol), and subsequently were opposed to emulsion coated coverslips. Specific binding of both alpha- and beta-receptors was demonstrated in the rat aorta. While specific beta-receptor binding was demonstrated in the rat jugular vein, this tissue showed no detectable alpha-receptors. These autoradiographic studies indicate that the lack of alpha-adrenergically mediated contraction in the rat jugular vein is likely due to a virtual absence of alpha-receptor binding sites, rather than poor functional alpha-receptor coupling.