Characterization of the effects of histamine in porcine tracheobronchial lymph vessels.

We characterized the responses of lymphatic vascular smooth muscle to histaminergic-receptor stimulation and blockade and explored the mechanisms underlying the histamine-stimulated release of endothelium-derived relaxing factor (EDRF). Fresh porcine tracheobronchial lymph vessel rings mounted in organ baths were stimulated by the cumulative addition of histamine or H1, H2, and H3 receptor-specific agonists in the presence or absence of receptor-specific antagonists. Histamine had a contractile effect on lymphatic vascular smooth muscle that was H1 receptor mediated. No important effects were elicited by H2- or H3-receptor stimulation. Histamine also caused the release of EDRF as demonstrated by an increase in smooth muscle tone in the absence of endothelium and after inhibition of nitric oxide synthase. This effect was strong at high concentrations of histamine and was mediated by H1-receptor stimulation. The results suggest that histamine may contribute to the regulation of lymphatic vascular smooth muscle tone under pathological conditions, an effect that may be controlled through modification of H1-receptor activity.