Characterisation and distribution of vasoactive intestinal polypeptide binding sites in human brain

The binding of 125I-vasoactive intestinal polypeptide (VIP) to human brain membranes has been studied. The binding was saturable with a dissociation constant (KD) of 4.4 +/- 2.0 nM and maximum binding value (Bmax) of 8.6 +/- 6.2 fmoles/mg tissue (mean +/- SD, n = 4), and was displaced by unlabelled VIP with an IC50 of 4 nM; secretin was much less potent with an IC50 of approximately 8 microM. The regional distribution of 125I-VIP binding in human brain revealed highest binding values to be in frontal and temporal cortices with intermediate values in amygdala, caudate and cerebellum, with lowest values in hippocampus, substantia nigra and hypothalamus.