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Neurological transmitters including ACh, substance P (SP), and calcitonin gene-related peptide (CGRP) play an important role in regulating airway tone, and increased bronchial reactivity to cholinergic stimulation is a well-recognized phenomenon in patients with bronchial asthma. We postulated that ACh, SP, and CGRP might stimulate alveolar macrophages (AMs) to release neutrophil, monocyte, and eosinophil chemotactic activities. To test this hypothesis, bovine AMs were isolated by bronchoalveolar lavage and cultured. AMs released chemotactic activities in response to ACh in a dose- and time-dependent manner (P < 0.05). However, SP and CGRP did not stimulate bovine AMs. Checkerboard analysis revealed that these released activities were predominantly chemotactic. Partial characterization and molecular-sieve column chromatography revealed that low-molecular-weight lipid-soluble activity was predominant. Lipoxygenase inhibitors significantly blocked the release of chemotactic activities (P < 0.05). Leukotriene B4- and platelet-activating factor-receptor antagonists blocked the chemotactic activities. Immunoreactive leukotriene B4 significantly increased in supernatant fluids in response to ACh (P < 0.05), but platelet-activating factor did not. The receptor responsible for the release of the chemotactic activities was the muscarinic M3 receptor. These data demonstrate that ACh stimulates AMs to release lipoxygenase-derived chemotactic activities and plays a role in inflammatory cell recruitment into the airway.

We investigated the effects of leukotriene (LT) D4 and its novel potent and selective antagonist L-660,711 on isolated rat hearts with chronic myocardial infarction. The left coronary artery was ligated permanently or for 30 or 60 min and followed by reperfusion. Hearts were isolated and perfused in the Langendorff mode 4 days, 4 wk, or 8 wk after the operation. Dose-response curves for LTD4 (12-240 ng/min) on coronary flow were shifted to the left in rats with permanent coronary occlusion for 8 wk or with coronary occlusion for 30 or 60 min and reperfusion for 4 wk. In contrast, dose-response curves were unchanged in rats 4 days after myocardial infarction. L-660,711 shifted dose-response curves for LTD4 on coronary flow to the right in all groups. The negative inotropic and chronotropic effects of LTD4 could be markedly attenuated by L-660,711 in all groups. Our findings suggest that the effect of LTD4 is enhanced in rat hearts with chronic myocardial infarction. L-660,711 effectively antagonized the vasoconstrictor effect of exogenous LTD4.

The goal of this study was to characterize further the manner in which the peptide leukotriene (LT) D4 evokes endothelium-dependent relaxation of the canine renal vein (RV) and artery (RA). The effects of four chemically and structurally dissimilar LT receptor antagonists and pertussis toxin (PTX), on LTD4-evoked relaxation of RV and RA rings, were determined and compared. In the presence of ICI 198,615 (10(-5) M), relaxation of both the RA and RV evoked by LTD4 was markedly attenuated. MK-571 (10(-5) M) altered neither RA nor RV relaxation evoked by LTD4. Relaxation of the RV but not the RA, evoked by LTD4, was attenuated in the presence of LY171,883 (10(-5) M). L649,923 (10(-5) M) solely inhibited LTD4-evoked relaxation of the RA. Pretreatment of vascular rings with PTX (250 ng/ml) for 2 h attenuated the vasomotor relaxation evoked by LTD4 in the RA but not in the RV. These observations suggest that LTD4-evoked relaxation of the RA and RV is dependent on different mechanisms. The endothelium-dependent response produced in the RA apparently involves a PTX-sensitive G protein. It is proposed that multiple signal transduction pathways and perhaps different LTD4 receptors may account for the diverse activity of LTD4.