Bombesin-related peptides (BRP) are present in the lung during foetal life and are mitogenic for normal bronchial epithelial cells, pulmonary fibroblasts, and small-cell lung carcinoma cell lines. Increased levels of BRP have been described in the adult lung of cigarette smokers and in smoking related lung diseases. BRP have also been involved in the network of neuroimmune interactions, having been shown to modulate the phagocytic function of monocytes and alveolar macrophages. BRP have recently been shown to modulate the release of procoagulant activity (PCA) by human monocytes and alveolar macrophages after a 24 h culture. The aim of this study was to evaluate the effect of bombesin on cell-associated PCA of alveolar macrophages (AMs) obtained from asymptomatic subjects. In basal conditions, AMs were found to possess a low procoagulant activity, that was not affected by their preincubation (4 h at 37 degrees C) with phorbol myristate acetate (1 microgram-mL-1). On the contrary, endotoxin (lipopolysaccharide (LPS)) induced a significant increase of procoagulant activity of macrophages when used at a concentration of 1 microgram.mL-1, in the same experimental conditions; whilst a lower (1 ng.mL-1) concentration of LPS nonsignificantly enhanced cell-associated PCA. Treatment of AMs with synthetic bombesin (BN) alone (10(-6) to 10(-10) M) did not enhance cell-associated PCA, whilst a significant effect was seen when BN was added to the lower concentration of LPS (BN 10(-6) M+LPS 1 ng.mL-1: 12.6 U.10(-6) cells; LPS alone 1 ng.mL-1: 7.8 U.10(-6) cells).(ABSTRACT TRUNCATED AT 250 WORDS)