1 The effects of salmeterol, a novel long-actingf2-adrenoceptor agonist, have been investigated on antigen-induced mediator release from passively sensitized fragments of human lung in vitro.2 Salmeterol was a potent inhibitor of the release of histamine (-log IC5O = 8.54), leukotriene C4 (LTC4)/LTD4 (-log IC50 = 9.07) and prostaglandin D2 (-log IC50 = 8.81). It was slightly less potent (1-3 fold) than isoprenaline, but significantly more potent (10-35 fold) than salbutamol. 3 Propranolol competitively antagonized the inhibitory effects of salmeterol on histamine release (pA2 = 8.41) and LTCSLTD4 release, (pA2 = 8.40) indicating an action viaf,-adrenoceptors.4 The inhibitory effects of isoprenaline (20 nM) and salbutamol (200 nM) were removed after washing the lung tissue for 2 h and 4 h respectively. In contrast, the inhibitory effects of salmeterol (40 nM) were much longer-lasting, and were still evident after 20 h. 5 Salmeterol therefore exhibits potent and persistent inhibition of anaphylactic mediator release from human lung. This anti-inflammatory effect may be important for the therapeutic potential of salmeterol in the treatment of bronchial asthma.

The purpose of the present study was to classify adenosine receptors into A1 and A2 subtypes in a wide range of isolated tissues and cell types (rat adipocytes and atria, guinea‐pig ileum and atria (A1); guinea‐pig aorta, dog coronary artery and human platelets and neutrophils (A2)) using the R‐ and S‐diastereoisomers of N‐phenylisopropyladenosine (PIA), N‐cyclopentyladenosine (CPA), the novel compound, N‐[(1S,trans)‐2‐hydroxycyclopentyl]adenosine (GR79236), N‐[(2‐methylphenyl)methyl]adenosine (metrifudil), 2‐(phenylamino)adenosine (CV1808), and 2‐[[2‐[4‐(2‐carboxyethyl)phenyl]ethyl]amino]‐N‐ethylcarboxamidoadenosine (CGS21680); N‐ethylcarboxamidoadenosine (NECA) was used as a standard. Results obtained in all tissue preparations previously reported to contain A1‐receptors could be described by a single rank order of agonist potency: CPA ≥ GR79236, R‐PIA ≥ NEC A > > S‐PIA ≥ metrifudil ≥ CV1808, CGS21680. In contrast, two distinct rank orders of agonist potency were observed in preparations previously reported to contain A2‐receptors. In dog coronary artery, human neutrophils and platelets the rank order of potency was: CV1808, CGS21680 ≥ NECA > R‐PIA ≥ metrifudil ≥ CPA > GR79236, S‐PIA. However, in guinea‐pig aorta the rank order was: NECA > metrifudil > R‐PIA, CPA > CV1808, GR79236 ≥ S‐PIA, CGS21680. The results of this study are consistent with the existence of three types of adenosine receptor: A1‐and two subtypes of A2‐receptor. The receptor present in dog coronary artery, human platelets and neutrophils, probably corresponds to the A2a subtype, whilst that present in the guinea‐pig aorta may be of the A2b subtype.

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These results indicate that stimulation of adenosine A3 receptors both enhances degranulation in vitro and directly produces degranulation of rat mast cells in vivo.

1 The aims of this study were to characterize the EP receptor subtype mediating the inhibition of superoxide anion generation by formyl methionyl leucine phenylalanine (FMLP)-stimulated human neutrophils, and to test the hypothesis that adenosine 3':5'-cyclic monophosphate (cyclic AMP) is the second messenger mediating the inhibition of the neutrophil by prostaglandin (PG)E2. 2 PGE2 (0.001-10 ItM) inhibited FMLP (100 nM)-induced 02-generation from human peripheral blood neutrophils in a concentration-dependent manner, with an ECM of 0.15 ± 0.03 AM, and a maximum effect ranging from 36-84% (mean inhibition of 68.7 ± 2.5%, n = 32).3 The EP2-receptor agonists, misoprostol, l1-deoxy PGE1, AH13205 and butaprost, all at 1OpM, inhibited°2-generation, causing 95.5 ± 2.9%, 56.8 ± 5.2%, 37.1 ± 6.6% and 18.9 ± 4.4% inhibition respectively, the latter two being much less effective than PGE2. Similarly, the EPI-receptor agonist, 17-phenyl PGE2 (101sM), and the EP3/EPI-receptor agonist, sulprostone (10I1M), also inhibited 02-generation, causing 32.2 ± 7.0% and 15.3 ± 3.4% inhibition respectively. 4 The non-selective phosphodiesterase inhibitor, isobutyl methylxanthine (IBMX, 0.25 mM) inhibited the FMLP response by 54.5 ± 5.0%. In addition, IBMX shifted concentration-effect curves for PGE2, misoprostol, I 1-deoxy PGEI, butaprost, and AH 13205 to the left, to give ECms of 0.04 ± 0.03 (n = 13), 0.07 ± 0.03 (n = 4), 0.08 ± 0.03 (n = 4), 0.33 ± 0.13 (n = 4) and 0.41 ± 0.2 gM (n = 3) respectively, allowing equieffective concentration-ratios -(EECs, PGE2 = 1) of 11.5, 5.3, 50.7 and 12.7 to be calculated. This agrees well with the relative potencies of these agonists at EP2 receptors. 5 By contrast, even in the presence of IBMX (0.25 mM), sulprostone and 17-phenyl PGE2 were only effective at the highest concentration (10 gM), and gave EECs of > 700 and 486 respectively, suggesting that EP1 or EP3 receptors are not involved. 6 The selective type IV phosphodiesterase inhibitor, rolipram at 2 and 10 nM did not inhibit the FMLP response, but at the higher concentration of 50 nM, it decreased the FMLP response by 46.6 7.3%.However, rolipram shifted concentration-effect curves for PGE2 to the left to give EC50s of 0.06 0.022, 0.015 + 0.0, 0.012 ± 0.006 tM at 2, 10 and 50 nM respectively, compared to the control EC50 of 0.27 ± 0.09 pM for PGE2. 7 The EP4/TP receptor blocking drug, AH 23848B (10 AM, 10 min) did not inhibit 02-generation by PGE2, but was found to potentiate significantly the effect of PGE2 at the lower concentrations of PGE2 tested (0.001-0.1 M). 8 The adenylate cyclase inhibitor, SQ 22,536 (0.1 mM, 2 min) reduced PGE2-induced inhibition of 02-production, giving an EC50 in the absence of SQ 22,536 of 0.24 ± 0.1, and 1.9± 1.1 AM in its presence.9 These results suggest that inhibition of superoxide generation by PGE2 is mediated by stimulation of EP2 receptors and activation of adenylate cyclase, leading to the elevation of intracellular levels of cyclic AMP.