The effect of lipoxygenase inhibitors and leukotriene antagonists on anaphylaxis

Anti-anaphylactic action of nordihydroguaiaretic acid in antigen sensitized guinea pigs

Therapeutic natural products and medicinal herbs has gained popularity. The anti-antigenic action of the plant alkaloid nordihydroguaiaretic acid (NDGA) was studied in ovalbumin (OA)-sensitized guinea pigs. In one series of experiments conscious, non-sedated guinea pigs were challenged with OA aerosol. Specific airway resistance (SR_AW) was monitored using a two-chambered whole-body plethysmograph. OA aerosol increased SR_AW above that produced by vehicle administration. Prior NDGA administration by a 1min 0.9% aerosol (w/vol) attenuated the increase in SR_AW resulting from OA challenge. In the anesthetized guinea pig pretreated with indomethacin, pyrilamine and propranolol, intravenous OA injection increased intra-tracheal pressure above vehicle injection. Intravenous NDGA administration (5mg/kg) reduced the intra-tracheal pressure increases. In a third series of experiments plasma leukotriene C₄ was measured by radio-immunoassay in 3 groups challenged with OA aerosol: vehicle-treated OA-sensitized, OA-sensitized receiving NDGA and vehicle treated guinea pigs. NDGA pretreatment reduced plasma LTC₄ in response to OA challenge in OA sensitized guinea pigs. This study demonstrates that NDGA is an effective antigenic agent when given by aerosol or intravenous injection in either conscious or anesthetized guinea pigs, respectively. The mechanism of action of NDGA is presumed primarily be due to the blockage of 5-lipoxygenase and therefore the synthesis of leukotrienes.

Anti-ulcerogenic and anti-inflammatory activity of the methanolic extract of Larrea divaricata Cav. in rat

Larrea divaricata Cav. (Zygophyllaceae) is used in popular medicine as anti-inflammatory and anti-rheumatic drug, containing higher amounts of nordihydroguaiaretic acid, a well-known free radical scavenger. Here we describe the gastric anti-ulcerogenic effect of the methanolic extract of Larrea divaricata (LdME) leaves in rat, using absolute ethanol and HCl 0.6N as necrotizing agents, and the effect of blocking endogenous sulfhydryl (SH) groups with N-ethylmaleimide (NEM). We also studied the anti-inflammatory activity of LdME in two rat experimental models: cotton pellet induced granuloma and arthritis induced by adjuvant-carrageenan. Influence of treatment in body weight and some lymphoid organs was evaluated. Finally, the free radical scavenging capacity of LdME was determined by the method of 1,1-diphenyl-2-picrylhydrazyl (DPPH) inhibition. LdME demonstrated anti-ulcerogenic effect in rats, and it was shown that the endogenous SH compounds were not involved in the mechanism of action. LdME also showed inhibitory activity in the applied models of inflammation, being more effective in the acute phase. No effect was observed concerning the weight of spleen, thymus and body. The extract proved to possess elevated free radical scavenging capacity which may contribute to the observed gastric anti-ulcerogenic and anti-inflammatory activity.

GABA-mediated inhibition of the anaphylactic response in the guinea-pig trachea

1. In sensitized guinea-pigs, the effects of gamma-aminobutyric acid (GABA) and GABAmimetic drugs have been investigated on tracheal segments contracted by cumulative application of an allergen (ovoalbumin, OA) and on serosal mast cells. The same drugs have also been tested on activation of alveolar macrophages isolated from unsensitized guinea-pigs. 2. Superfusion with GABA (1-1000 microM) reduced the contraction intensity of tracheal strips. The effect of GABA (100 microM) was not affected by the carrier blockers, nipecotic acid and beta-alanine (300 microM each). It was mimicked by the GABAB agonist (-)-baclofen (100 microM) but not 3-aminopropanephosphinic acid (100 microM, 3-APA). The GABAA agonist, isoguvacine (100 microM) did not exert any effect. GABA (10 microM)-induced inhibition of tracheal contractions was reduced by the GABAB antagonist, 2-hydroxysaclofen (100 microM, 2-HS), but not by the GABAA antagonist, bicuculline (30 microM). 3. The reduction in contraction intensity induced by GABA (100 microM) was prevented by a 40 min preincubation of tracheal strips with capsaicin (10 microM), but not tetrodotoxin (TTX, 0.3 microM). The effect of GABA (1000 microM) was absent after preincubation with indomethacin (2.8 microM) but unmodified when nordihydroguaiaretic acid (NDGA, 3.3 microM) was used. Finally, removal of the epithelium prevented the GABA effect. 4. Anaphylactic histamine release from serosal mast cells isolated from sensitized animals was not affected either by GABA (10-1000 microM) or the selective receptor agonists (-)-baclofen (0.1-1000 microM) and isoguvacine (10-1000 microM). The release of platelet-activating factor (PAF) from alveolar macrophages stimulated by formyl-Met-Leu-Phe (FMLP; 1 microM) was modified neither by GABA (100 microM)nor by (-)-baclofen (100microM).5. In conclusion, these data show that GABA can inhibit allergic phenomena in the guinea-pig airways through activation of GABAB receptors. An involvement of neuropeptidergic sensory structures is suggested but a role for epithelial cells and arachidonate metabolites is not definitely proved.