Presynaptic and Postsynaptic a2"Adrenergic Receptors in Human Cerebral Arteries and Their Alteration After Subarachnoid Hemorrhage

The nature of a-adrenergic receptors in human cerebral arteries was characterized, and alteration of these receptors after subarachnoid hemorrhage was examined using a radioligand binding assay. Norepinephrine content of control arteries was also analyzed and compared with that of arteries after subarachnoid hemorrhage. Norepinephrine content in human cerebral arteries in cases of subarachnoid hemorrhage was about 5% of the control group. Specific binding of [H]yohimbine, a selective a2antagonist, to cerebral arteries of the control group indicated two classes of binding sites: high-affinity sites with KD of 0.5 nM and B m of 18 fmol/mg protein and low-affinity sites with KD of 29 nM and B ^ of 248 fmol/mg protein. In cerebral arteries obtained from the subarachnoid hemorrhage group, pH]yohimbine binding sites were of a single class with KD of 53 nM and B^, of 456 fmol/mg protein. These results suggest that sympathetic denervation and subsequent alterations in a2-adrenergic receptors occurred after subarachnoid hemorrhage in human cerebral arteries. These changes in sympathetic innervation to cerebral arteries were considered to be one of the antecedents of delayed vasospasm after subarachnoid hemorrhage. (5troJcel988;19:80-83)