Bronchoconstriction and endogenous nitric oxide in isolated lungs of spontaneously hypertensive rats Fa ´bio H. Kwasniewski a , Richardt Gama Landgraf a , Yeshwant S. Bakhle b , Sonia Jancar a, * a Department of Immunology, Institute of Biomedical Sciences, University of Sa ˜o Paulo, Av. Prof. Lineu Prestes 2415, 05508-900 Sa ˜o Paulo, Brazil b Leukocyte Biology, Division of Biomedical Sciences, Faculty of Medicine, Imperial College, London SW7 2AZ, UK Received 26 January 2004; accepted 3 February 2004 Abstract Bronchoconstrictor responses were measured in lungs isolated from spontaneously hypertensive (SHR) and normotensive rats, perfused via the airways. Lungs from SHRs were more responsive than lungs from normotensive rats to methacholine, 5-hydroxytryptamine (5-HT), arachidonic acid or prostaglandin H 2 . The responses of SHR airways to methacholine or 5-HT were unaffected by pretreatment in vivo with an inhibitor of nitric oxide (NO) synthase, N N -nitro-L-arginine methyl ester hydrochloride (L-NAME, 30 mg kg À 1 ), although responses in normotensive airways to methacholine, but not to 5-HT, were enhanced. Antigen challenge of isolated lungs from actively sensitized rats elicited bronchoconstriction, not different between strains. Pretreatment with L-NAME increased the response to antigen challenge only in normotensive lungs. Compound 48/80 induced bronchoconstriction in lungs from either strain, equally. These responses to compound 48/80 were unaffected by L-NAME pretreatment. Thus, SHR airways lack relaxing factors and degranulation of mast cells in SHR lungs was not affected by endogenous NO. D 2004 Elsevier B.V. All rights reserved. Keywords: Bronchoconstriction; Lung; NO (Nitric oxide); Mast cell; Anaphylaxis; Spontaneously hypertensive, rat 1. Introduction Bronchoconstriction is one of the acute responses to immunological challenge in the lung and has been long considered to reflect the release of a variety of smooth muscle spasmogens from mast cells in the process referred to as degranulation (Metcalfe et al., 1997; Black, 2002). In earlier work we had found that the mast cells in mesentery and skin of spontaneously hypertensive rats (the SHR strain) were resistant to degranulation following challenge with antigen in sensitised animals (Kwasniewski et al., 1998). It was there- fore possible that the constrictor response to immunological challenge in the airways of lungs isolated from SHR, actively sensitised to ovalbumin, would be also decreased, relative to that in lungs from similarly treated normotensive rats. As we used the isolated lungs as both the generator of, and the assay for, the mixture of spasmogens released during antigen challenge, we also measured bronchoconstriction to known, standard agonists such as methacholine and 5-hydroxytryp- tamine (5-HT) to allow for any intrinsic difference in airway smooth muscle between strains. Such strain-related differ- ences have already been shown for the vascular smooth muscle in the mesenteric bed (Chang et al., 2002; Liu et al., 2002; Touyz et al., 2002). Furthermore, since nitric oxide (NO) has been shown to be an inhibitor of smooth muscle contraction (see Nijkamp and Folkerts, 1995; Ignarro, 2002) and of mast cell degranulation (Forsythe et al., 2001; Cole- man, 2002), any strain-related differences in bronchocon- striction following antigen challenge could also be a reflection of differences in endogenous NO generation in lung tissue. To assess this possibility in our model, synthesis of endogenous NO was inhibited with the nonselective NO synthase inhibitor, N N -nitro-L-arginine methyl ester hydro- chloride (L-NAME; Hobbs et al., 1999). Our experiments were therefore designed to test two main hypotheses. Firstly, that the SHR airways would exhibit less bronchoconstriction after antigen challenge, than airways from normotensive rats. The second hypoth- esis was that any decreased response in the SHR airways would reflect inhibition of the response by endogenous NO and thus would be reversible by treatment with L-NAME. Our results have been complicated by the observation that airways in lungs from SHR were more responsive to 0014-2999/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ejphar.2004.02.005 * Corresponding author. Tel./fax: +55-11-3091-7744. E-mail address: sojancar@icb.usp.br (S. Jancar). www.elsevier.com/locate/ejphar European Journal of Pharmacology 488 (2004) 181 – 189