Abstract
In order to determine whether or not α-adrenoceptors are present in adrenal glands, radioligand receptor binding assay was performed in both Sprague-Dawley (SD) rat and human adrenal gland membranes.
Radioligand binding assay using 3H-prazosin as an α1-adrenoceptor ligand and 3H-yohimbine as an α2-adrenoceptor ligand, clearly demonstrated alphal and alpha2 receptors present in both rat and human adrenal gland membranes. Maximal binding capacity (Bmax) and dissociation constant (Kd) of 3H-prazosin binding to the rat adrenal gland were 12.5fmol/mg protein, and 0.11nM, respectively. Those for the membrane preparations from adrenal cortex and medulla of the normal human were 16.3fmol/mg protein, 0.34nM and 16.3fmol/mg protein, 0.27nM, respectively. And those of the human pheochromocytoma were 25.6fmol/mg protein, 0.15nM, respectively. On the other hand, Bmax and Kd of 3H-yohimbine binding in the rat adrenal gland to were 22.9fmol/mg protein, and 4.28nM, respectively. Those for the membrane preparations from adrenal cortex and medulla of the normal human were 40.4fmol/mg protein, 5.15nM and 12.2fmol/mg protein, 5.39nM, respectively. And those of the human pheochromocytoma were 35.8fmol/mg protein, and 1.08nM, respectively.
Bmax (35.8fmol/mg protein) of 3H-yohimbine binding in the pheochromocytoma was significantly (p<0.01) greater than that (12.2fmol/mg protein) in the human normal adrenal medulla, while Kd (1.08nM) of this binding in the human pheochromocytoma was significantly (p<0.01) lower than that (5.39nM) in the human normal adrenal medulla. Our data suggest that the alpha2 receptor had greater affinity and binding site density to its agonist in the human pheochromocytoma than in the human normal adrenal medulla.
