Increased density of I-2-imidazoline receptors in human glioblastomas

A glial location has been proposed for the non-adrenoceptor [H-3]idazoxan binding site termed the I-2-imidazoline receptor. The specific binding of [H-3]idazoxan in the presence of (-)adrenaline was measured in membranes from excised human glioblastomas (n = 6), meningiomas (n = 6) and normal brains (n = 6). The pharmacological profile of the [H-3]idazoxan binding in astrocytic tumours was similar to that in normal brain, compatible with the presence of I-2-imidazoline receptors. There was a higher density of I-2-imidazoline receptors in astrocytic tumours (B-max = 266 +/- 18 fmol mg(-1) protein; p < 0.001) than in normal brain (B-max = 54 +/- 4 fmol mg(-1) protein), with no differences in affinity values. Almost no [H-3]idazoxan- specific binding was shown in meningiomas. The results suggest that I-2-imidazoline receptors may be a selective marker for glial tumours in the evaluation of intracranial neoplasms.