Bi-affinity alpha 1-adrenoceptor binding in normal rat brain in vivo.
The specific binding in rat brain in vivo of [125I]HEAT ([125I]iodo-2-[beta-(4-hydroxyphenyl)ethylamino methyl), a selective alpha 1-adrenoceptor ligand, was analyzed by a method designed to distinguish sites with different affinities. The data indicate at least two sites with different affinities for the alpha 1-adrenoreceptor in normal rat brain in vivo: a high-affinity site with Kd (half-saturation constant) of 3.6 +/- 0.7 nM (AV +/- SD), and a low-affinity site with Kd of 668 +/- 552 nM. The density (Bmax) of the high-affinity site in nine brain regions--auditory, visual, sensorimotor (four layers) and frontal cortex and lateral thalamic and medial geniculate nuclei--varied from 2.2 +/- 0.8 to 14.6 +/- 0.6 pmole/g, while the low-affinity range was 149 +/- 44 to 577 +/- 30 pmole/g. The results also revealed a very dynamic relationship between the two sites regulated by the concentration of the ligand ranging from 80% preponderance of the high-affinity sites at low ligand concentrations to more than 95% preponderance of the low-affinity sites at high ligand concentrations.
Gjedde
A
A
Positron Imaging Laboratories, McConnell Brain Imaging Center, Montreal, Quebec, Canada.
Dyve
S
S
Yang
Y J
YJ
McHugh
M
M
Pappius
H M
HM
D000818:Animals; D001345:Autoradiography / Q000379:methods; D001921:Brain / Q000378:metabolism*; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D008433:Mathematics; D008962:Models, Theoretical; D009928:Organ Specificity; D010627:Phenethylamines / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D012016:Reference Values; D044024:Tetralones
D007457:Iodine Radioisotopes; D010627:Phenethylamines; D011942:Receptors, Adrenergic, alpha; D044024:Tetralones; C048008:2-(beta-(3-iodo-4-hydroxyphenyl)ethylaminomethyl)tetralone