Expression of vasoactive intestinal peptide binding sites in rat peritoneal macrophages is stimulated by inflammatory stimulus.

Vasoactive intestinal peptide (VIP) binding to resident and stimulated-rat peritoneal macrophages was studied. No specific VIP binding was obtained with resident rat peritoneal macrophages. In contrast, VIP bound specifically to casein-elicited macrophages. The Scatchard analysis of binding data was consistent with the presence of two classes of VIP binding sites, but may represent a receptor site and internalized VIP. Both specific VIP binding and number of specific high affinity binding sites for VIP augmented progressively after sodium caseinate injection, reaching maximum at days 4-5. Macrophages obtained 1 day after injection showed a minimal specific VIP binding (0.3 +/- 0.1% of total), but cells obtained 4 days after injection showed a maximal binding to the peptide (3.1+/-0.2% of total). The number of high affinity binding sites per cell raised also progressively after sodium caseinate injection: 2650+/-301 at day 2, 4939 +/-723 at day 3, 6684+/-903 at day 4 and 9636+/-1626 at day 5 (P = 0.0035). The number of low affinity binding sites per cell exhibited the same changes. In contrast, the Kd values of both high and low affinity VIP binding sites did not vary significantly (P>0.05). These results demonstrate that VIP binding sites are only displayed by stimulated macrophages, suggesting that VIP binding sites could be considered to be a pre-activation marker in macrophages and could be used to recognize inflammatory or stimulated macrophages.