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 o btained with resident rat peritoneal macrophages: In contrast, VIP bou nd specifically to casein-elicited macrophages. The Scatchard analysis of binding data was consistent with the presence of two classes of VI P binding sites, but may represent a receptor site and internalized VI P. Both specific VIP binding and number of specific high affinity bind ing sites for VIP augmented progressively after sodium caseinate injec tion, reaching maximum at days 4-5. Macrophages obtained 1 day after i njection showed a minimal specific VIP binding (0.3 +/- 0.1% of total) , but cells obtained 4 days after injection showed a maximal binding t o the peptide (3.1 +/- 0.2% of total). The number of high affinity bin ding sites per cell raised also progressively after sodium caseinate i njection: 2650 +/- 301 at day 2, 4939 +/- 723 at day 3, 6684 +/- 903 a t day 4 and 9636 +/- 1626 at day 5 (P = 0.0035). The number of low aff inity binding sites per cell exhibited the same changes. In contrast, the K-d values of both high and low affinity VIP binding sites did not vary significantly (P > 0.05). These results demonstrate that VIP bin ding sites are only displayed by stimulated macrophages, suggesting th at VIP binding sites could be considered to be a pre-activation marker in macrophages and could be used to recognize inflammatory or stimula ted macrophages.