Occurrence, distribution and possible role of the regulatory peptide endothelin in the nasal mucosa

Expression of endothelin A- and B-receptors in human nasal mucosa

Several studies have suggested an important role for the endothelin (ET) family of peptides in the vascular regulation of the nose. In addition, there is increasing evidence that ETs play a role in allergic airway inflammation. Endothelin is produced locally in the nose and mediates its effects via two distinct receptor subtypes, termed ET(A) and ET(B). Using reverse transcriptase-polymerase chain reaction, mRNAs encoding ET(A)- and ET(B)-receptors were detected in the human lower turbinate and sinus mucosa. The possibility of local release of ETs in connection with specific target receptors suggests a role for endothelin in the regulation of vascular tone, glandular secretion and epithelial functions.

Endothelins and asthma

In the decade since endothelin-1 (ET-1) and related endogenous peptides were first identified as vascular endothelium-derived spasmogens, with potential pathophysiological roles in vascular diseases, there has been a significant accumulation of evidence pointing to mediator roles in obstructive respiratory diseases such as asthma. Critical pieces of evidence for this concept include the fact that ET-1 is an extremely potent spasmogen in human and animal airway smooth muscle and that it is synthesised in and released from the bronchial epithelium. Importantly, symptomatic asthma involves a marked enhancement of these processes, whereas asthmatics treated with anti-inflammatory glucocorticoids exhibit reductions in these previously elevated indices. Despite this profile, a causal link between ET-1 and asthma has not been definitively established. This review attempts to bring together some of the evidence suggesting the potential mediator roles for ET-1 in this disease.

Endothelin and nitric oxide synthase in lymphatic endothelial cells: immunolocalization in vivo and in vitro

BACKGROUND

Endothelin (ET) is an endothelium-derived multifunctional peptide that produces a potent, long-lasting vasoconstriction. Nitric oxide (NO), besides being the most important endothelium-derived relaxant factor in blood vessels, is supposed to be involved in regulating the interactions among endothelium, adhesive molecules, and leukocytes.

METHODS

We investigated the possible occurrence and distribution of ET and constitutive nitric oxide synthase (NOs), the enzyme that generates NO from L-arginine, in bovine lymphatic vessels and primary culture of lymphatic endothelium by using immunocytochemistry.

RESULTS

Specific immunostaining with both ET and endothelial constitutive NOs antisera was detectable at light and electron microscopic levels in the endothelial cell layer of lymphatic vessels, whereas no immunostaining could be observed in the muscular and adventitial layers. The immunoreaction showed a diffuse pattern throughout the cytoplasm of endothelial cells. Primary cultures of endothelial cells isolated from lymphatic vessels also displayed cytoplasmic ET- and NOs-like immunoreactivities. The endothelial nature of cell monolayers was confirmed by the positive reaction to the von Willebrand factor, a reliable marker of endothelial cells, and by ultrastructural features of cultured cells.

CONCLUSIONS

These findings suggest that the endothelium is a major source of ET and NO in lymphatic vessels. Interestingly, the lymphatic endothelium maintains the capability of producing such vasoactive sustances also in vitro, thus suggesting that lymphatic endothelial cells in culture may be used in studies concerning the role of the endothelium in the generation of vasoactive molecules. According to previous functional studies, the occurrence of ET and NOs immunoreactivities in lymphatic vessel endothelium supports the view that lymphatic endothelium may play an important role in the regulation of lymphatic vascular tone and in the production of vascular contractile activity promoting lymph flow.

Endothelin-induced vasoconstriction in rabbit nasal mucosa

Nasal blood flow is finely regulated by local release of neurotransmitters, neuropeptides and other bioactive molecules acting via paracrine mechanisms. We have investigated the effects of endothelin-1 (ET-1), a potent vasoconstrictor peptide, on the blood perfusion of rabbit nasal mucosa by laser Doppler flowmetry. After injection with ET-1, a potent and prolonged nasal vasoconstriction was observed. ET-immunoreactivity has previously been detected in nasal tissues and it is therefore suggested that ET-1 may participate in the regulation of nasal blood flow via paracrine mechanisms.