Quantitative and autoradiographic analyses of alpha-adrenergic and serotonergic receptors on aorta and coronary...

Norepinephrine, epinephrine, and 5-hydroxytryptamine (5-HT) modulate the vascular tone via specific receptors on the vascular wall. Binding characteristics and localization of alpha-adrenergic and serotonergic receptors were determined in porcine aortas and coronary arteries. Radioligand binding studies were done using frozen sections of vascular tissue (10 microns thick), and the obtained data were compared with findings on microsomal fractions prepared from smooth muscle cells. Affinities [dissociation constant (Kd)] of 125I-labeled 2-[beta-(4-hydroxyphenyl)-ethylaminomethyl]-tetralone (BE 2254), an alpha 1-antagonist, for alpha-adrenergic receptors on aortic and coronary microsomal fractions were 190 and 224 pM, respectively. The Kd of 125I-labeled lysergic acid diethylamide (LSD), a serotonergic antagonist, to serotonergic receptors on the aorta was 403 pM, a value less than that obtained for the coronary artery (873 pM, p less than 0.01). The Kd of 125I-BE 2254 on tissue sections from the aorta was 164 pM and did not significantly differ from that obtained for microsomal fractions. Inhibition constants of adrenergic agonists and antagonists for specific 125I-BE 2254 binding on aortic sections were identical with those obtained for microsomal fractions. Receptor densities examined by 125I-BE 2254 and 125I-LSD were higher in the aorta than in the coronary artery. 125I-BE 2254 bound specifically to alpha 1-adrenergic and 125I-LSD to 5-HT1-like receptors. Radiodensities of 125I-BE 2254 and 125I-LSD were homogeneous macroscopically across the aortic media. Silver grains distributed homogeneously over the smooth muscle cells across the media. There was no accumulation of silver grains to the intima.(ABSTRACT TRUNCATED AT 250 WORDS)