Adenosine A1 receptor antagonist versus montelukast on airway reactivity and inflammation.

Adenosine produces bronchoconstriction in allergic rabbits, primates, and humans by activating adenosine A(1) receptors. Previously, it is reported that a high dose of L-97-1, a water-soluble, small molecule adenosine A(1) receptor antagonist, blocks early and late allergic responses, and bronchial hyper-responsiveness to histamine in a hyper-responsive rabbit model of allergic asthma. Effects of a lower dose of L-97-1 are compared to montelukast, a cysteinyl leukotriene-1 receptor antagonist on early allergic response, late allergic response, bronchial hyper-responsiveness, and inflammatory cells in bronchoalveolar lavage (BAL) fluid following house dust mite administration. Rabbits received intraperitoneal injections of house dust mite extract within 24 h of birth followed by booster house dust mite injections. Hyper-responsive rabbits received aerosolized house dust mite (2500 allergen units), 1 h after intragastric administration of L-97-1 (1 mg/kg) or montelukast (0.15 mg/kg) and lung dynamic compliance was measured for 6 h. Lung dynamic compliance was significantly higher following L-97-1 at all time points and with montelukast at 60-300 min following house dust mite (P<0.05). L-97-1 blocks both early and late allergic responses. Montelukast blocks only the late allergic response. Both L-97-1 and montelukast significantly blocked bronchial hyper-responsiveness at 24 h (P<0.05). Both L-97-1 and montelukast significantly reduced BAL eosinophils at 6 h and neutrophils at 6 and 24 h (P<0.05). L-97-1 significantly reduced BAL lymphocytes at 6 and 24 h (P<0.05). Montelukast significantly reduced BAL macrophages at 6 and 24 h (P<0.05). By blocking both bronchoconstriction and airway inflammation, L-97-1 may be an effective oral anti-asthma treatment.

Salt-Induced hypertension in rats alters the response of isolated aortic rings to cromakalim

The effect of cromakalim, an opener of ATP-sensitive potassium (K atp) channel, on precontracted aortic rings from control and salt-loaded rats was studied in spague-Dawley rats. Salt-loading experiments involved the induction of hypertension by 6-week feeding of 80 g sodium chloride(NaCl)per kilogram(kg) diet while the control diet had 3 g NaCl per kg diet. Blood pressure and heart rate were determined by cannulation of a femoral artery under urethane/a-chloralose anaesthesia. Isolated aortic rings were mounted in tissue baths for isometric tension measurement. The sodium-potassium adenosine triphosphstase (Na-KATPase) pump activity was measured by potassium(K)-induced relaxation (with or without ouabain) following precontraction with 10-7 M noradrenaline.The KATP channel was studied by measuring the relaxation response to cromakalim,precontracted with either 10-7M noradrenalineor 60mM potassiumchloride(KCl). The Na- k ATPase pump appeared to be inhibited during salt loading. ATPase inactivation was found to be ouabain sensitive but did not seem to affect subsequent K - induced contraction. Cromakalim produced relaxation of noradrenaline precontracted rings frem the control rats; rings from salt-loaded rats showed significantly less relaxtion than control(p<0.05) under similar conditions. During K-induced precontraction, cromakalim produced a weak biphasic response in the control rings-an initial relaxation and then a reversal. Cromakalim produced further contraction of K-induced precontraction in salt-loaded group. The results suggest that ATP-sensitive potassium channels and Na-K ATPase pumps on the vascular smooth muscle membrane may be deactivated in the development of hypertension during salt loading.(AU)