It is widely accepted that peripheral injury increases spinal inducible cyclooxygenase (COX-2) expression and prostaglandin E 2 (PGE 2 ) formation as key mediators of nociceptive sensitization. Here, we used inducible nitric oxide synthase (iNOS) genedeficient (iNOSϪ/Ϫ) mice to determine the contribution of iNOSderived nitric oxide (NO) to this process. iNOSϪ/Ϫ mice exhibited reduced thermal hyperalgesia after zymosan injection. Spinal NO and PGE 2 formation both remained at baseline levels, in contrast to wild-type (wt) mice. In wt mice reduced hyperalgesia similar to that seen in iNOSϪ/Ϫ mice was induced by local spinal, but not by systemic treatment with the iNOS inhibitor L-NIL, suggesting that the reduced heat sensitization in iNOSϪ/Ϫ mice was attributable to the lack of spinal rather than peripheral iNOS. Two additional observations indicate that the antinociceptive effects of iNOS inhibition are dependent on a loss of stimulation of PG synthesis. First, intrathecal injection of the COX inhibitor indomethacin, which exerted pronounced antinociceptive effects in wt mice, was completely ineffective in iNOSϪ/Ϫ mice. Second, treatment with the NO donor RE-2047 not only completely restored spinal PG production and thermal sensitization in iNOSϪ/Ϫ mice but also its sensitivity to indomethacin. In both types of mice induction of thermal hyperalgesia was accompanied by similar increases in COX-1 and COX-2 mRNA expression. The stimulation of PG production by NO therefore involves an increase in enzymatic activity, rather than an alteration of COX gene expression. These results indicate that NO derived from spinal iNOS acts as a fast inductor of spinal thermal hyperalgesia. Key words: nitric oxide; inducible nitric oxide synthase; zymosan; thermal hyperalgesia; paw edema; spinal microdialysis; L-NIL; RE-2047; prostaglandins; cyclooxygenaseAcute tissue damage is often accompanied by the fast development of hyperalgesia and allodynia (Andrew and Greenspan, 1999). Both peripheral mechanisms at the site of injury and central processes particularly in the spinal cord contribute to this phenomenon. Prostaglandins (PGs) Brune, 1994) as well as nitric oxide (NO) (Lawand et al., 1997) are produced in response to tissue damage peripherally and centrally. Whereas PGs are generally accepted to play a dominant role in nociceptive sensitization (Bley et al., 1998), the role of NO is less clear. Also some authors claim of an anti-nociceptive action of NO (Goettl and Larson, 1996;Hamalainen and Lovick, 1997), most favor a pronociceptive activity Kawabata et al., 1994;Chen and Levine, 1999). Part of this controversy may arise from the existence of three different isoenzymes of NO synthase (NOS) (Gonzalez-Hernandez and Rustioni, 1999), which may have distinct effects on nociception, and from the lack of specific inhibitors for these different isoforms. In the CNS including the spinal cord, NO is thought to be primarily produced by the neuronal isoform of NOS (nNOS) (Downen et al., 1999). However, endothelial NOS is also found in neur...

The results show that iNOS is upregulated in the inflamed tissue and spinal cord with a similar time course. The effects obtained with L-NIL suggest that iNOS differently contributes to the inflammatory and nociceptive response induced by zymosan.

Twenty five new triazolecarboxamides related to YC-1 were prepared and tested for their antiplatelet (in vitro) and antithrombotic (in vivo) activities. Five of them inhibited the aggregation of blood platelets (Born test, inducer collagen) with IC50 values between 90 and 130 microM. Nine compounds exhibited significant antithrombotic properties with an inhibition of thrombus formation between 11 and 7%. Only one compound (8c) showed both, in vitro and in vivo effects. In vitro, the most active compounds were 11c and 12d. They inhibit platelet aggregation with IC50 = 90 and 95 microM. In vivo, 10a showed the strongest inhibition of thrombus formation with 11% in arterioles (5% in venules) after a single oral dose of 60 mg/kg. With serotonin as inducer both, 11c and 12d, showed lower IC50 values namely 25 or 30 microM, respectively. Additional antiplatelet activities were found for 11c against adrenaline (IC50 = 25 microM) and for 12d against platelet activating factor (PAF) (IC50 = 15 microM) as inducer.

Ten new 1, 2, 4-oxadiazole- and six new 1, 3, 4-oxadiazole-carboxamides containing different lipophilic moieties (i.e. 4-biphenyl-, 1-naphthyl, phenylpropyl- and n-hexyl substituents) and additional basic groups which are mainly alkyl- and dialkylaminoalkyl residues have been synthesized and tested for antiplatelet effects in vitro (Born-test) and antithrombotic properties in vivo (laser thrombosis model). If the platelet aggregation was induced by collagen, the inhibitory effects (IC50) were between 58 microM and 300 microM. Using serotonin (5-HT) as an inducer, compound 6a (N-(3-dimethylaminopropyl-5-(biphenyl-4-yl)-1, 3, 4-oxadiazole-2-carboxamide) had an IC50 = 1 microM (12e: (N-3-Dimethylaminopropyl)-3-(1-naphthyl)-1, 2, 4-oxadiazole-5-carboxamide, 6.7 microM). In an in vitro rat tail artery assay 6a and 12e behaved as a competitive 5-HT2A receptor antagonist (6a: pKB = 6.86 +/- 0.04; 12e: pKB = 6.66 +/- 0.05). The antithrombotic effects of some compounds were small but significant (7-10 % inhibition of thrombus formation).

Five 1-oximino-1-nitro compounds (nitrolic acids) were prepared and tested for antithrombotic and blood pressure lowering activities. 1-Nitro-ethanone 1-oxime (1, ethylnitrolic acid) 2 h after oral administration to rats inhibited thrombus formation by a laser beam in mesenteric arterioles of rats by 69% and by 46% in venules (60 mg/kg). The blood pressure of SHR rats even at this high dose only was decreased by 10% suggesting that antithrombotic and blood pressure effects can be dissociated. The in vitro decomposition of 1 at 37 degrees C nearly exclusively gave N2O and acetic acid indicating that HNO primarily had been formed.