Relaxation of cat tracheobronchial and pulmonary arterial smooth muscle by vasoactive intestinal peptide: lack of influence by peptidase inhibitors.
Vasoactive intestinal peptide (VIP) caused concentration-dependent relaxation in precontracted segments of trachea, hilar bronchus, intrapulmonary bronchus and intrapulmonary artery (IPA) isolated from cat lungs. VIP-induced relaxation responses were abolished by preincubation of tissues with the proteolytic enzyme, alpha-chymotrypsin (2 units ml-1). At the concentration employed, alpha-chymotrypsin treatment did not adversely affect tissue viability as isoprenaline and bethanechol continued to relax airways and IPA, respectively. Aprotinin prevented enzymatic degradation of VIP by alpha-chymotrypsin as demonstrated by the ability of VIP to relax tissues incubated with both the peptidase inhibitor and alpha-chymotrypsin. A spectrum of peptidase inhibitors, including aprotinin, leupeptin, bestatin, bacitracin, beta-phenylpropionic acid and captopril, individually or in combination, did not augment the relaxant effects of VIP in isolated pulmonary tissues. These results suggest that local enzymatic degradation may not be a primary route for inactivation of VIP in cat isolated airways and IPA. If VIP acts as a neurotransmitter in these tissues, a mechanism other than enzymatic proteolysis may be responsible for terminating its action.
D000403:Airway Resistance / Q000187:drug effects*; D000818:Animals; D001626:Bethanechol Compounds / Q000494:pharmacology; D001980:Bronchi / Q000187:drug effects; D002415:Cats; D005260:Female; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D018377:Neurotransmitter Agents / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology*; D014132:Trachea / Q000187:drug effects; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology*
D001626:Bethanechol Compounds; D018377:Neurotransmitter Agents; D011480:Protease Inhibitors; D014660:Vasoactive Intestinal Peptide; D007545:Isoproterenol