Increased density of I2-imidazoline receptors in human glioblastomas.

A glial location has been proposed for the non-adrenoceptor [3H]idazoxan binding site termed the I2-imidazoline receptor. The specific binding of [3H]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 [3H]idazoxan binding in astrocytic tumours was similar to that in normal brain, compatible with the presence of I2-imidazoline receptors. There was a higher density of I2-imidazoline receptors in astrocytic tumours (Bmax = 266 +/- 18 fmol mg-1 protein; p < 0.001) than in normal brain (Bmax = 54 +/- 4 fmol mg-1 protein), with no differences in affinity values. Almost no [3H]idazoxan-specific binding was shown in meningiomas. The results suggest that I2-imidazoline receptors may be a selective marker for glial tumours in the evaluation of intracranial neoplasms.