Relevance of VIP Cleavage Sites

The physiological relevance of these cleavage sites can be inferred from studies of the effects of enzyme inhibitors on VIP responses. For example, VIP-induced pulmonary relaxation can be attenuated by exogenous mast cell tryptase or chymase in the ferret (Franconi et al., 1989) and by exogenous a-chymotrypsin or papain in the guinea-pig. Enzyme inhibitor studies have provided insight into which of these enzyme systems are involved in the limitation of VIP activity. In cat airways, a combination of inhibitors that did not include an NEP inhibitor feiled 

through disruption of the balance between contractile and relaxant neuropeptides in the lung, inflammadon can promote non-specific airway hyper-responsiveness. It is increasingly clear that regulatory enzymes affect both contractile and relaxant pathways. The implication is that the net effect of altered enzyme activity must be judged by assessing changes in the metabolism of both the relevant relaxant and the relevant contractile peptides. 

The discovery that mammalian cells can produce oxidized forms of nitrogen that serve as neurotransmitters has had 

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