Characterization of the novel nitric oxide synthase inhibitor 7‐nitro indazole and related indazoles: antinociceptive and cardiovascular effects

Abstract

1 7-Nitro indazole (7-NI, 10-50mgkg-'), 6-nitro indazole and indazole (25-100mgkg-') administered i.p. in the mouse produce dose-related antinociception in the late phase of the formalin-induced hindpaw licking and acetic acid-induced abdominal constriction assays. The EDm values (mg kg-') were as follows: 7-NI (27.5 and 22.5), 6-nitro indazole (62.5 and 44.0) and indazole (41.0 and 48.5) in the two assays respectively. 3-Indazolinone, 6 amino indazole and 6-sulphanilimido indazole (all 50 mg kg-') were without effect. With the exception of 5-nitro indazole (50 mg kg-') which produced sedation, none of the other indazole derivates examined caused overt behavioural changes. 2 The antinociceptive effect of 7-NI (25 mg kg-', i.p.) in the late phase of the formalin-induced hindpaw licking assay was partially (46.7 ± 16.2%, n = 18) reversed by pretreatment with L-but not D-arginine (both 50 mg kg', i.p.). 3 The time course of 7-NI induced antinociception in the mouse was correlated with inhibition of brain (cerebellum) nitric oxide synthase (NOS) activity. Maximum antinociceptive activity and NOS inhibition were detected 18-30 min following i.p. administration. In contrast, no antinociceptive effect or inhibition of cerebellar NOS was detected 75 min post-injection. 4 7-NI, 6-nitro indazole, indazole, 3-indazolinone and 6-amino indazole (all 50 mg kg-') failed to influence mean arterial pressure (MAP) over the 45 min after i.p. administration in the anaesthetized mouse. Similarly, 7-NI (25 mg kg-') administered i.v. in the anaesthetized rat did not increase MAP or influence the vasodepressor effect of i.v. injected acetylcholine (ACh) over the same period. 0.06 fLM, n = 6) in phenylephrine-precontracted rabbit aortic rings. 6 These data provide further evidence that antinociception following administration of 7-NI in the mouse results from inhibition of central NOS activity and is not associated with inhibition of in vivo vascular endothelial cells NOS. Accordingly, 7-NI (or a derivative thereof) may provide an alternative approach to the development of novel antinociceptive drugs.

Effect of 7‐nitro indazole on neurotransmission in the rat vas deferens: mechanisms unrelated to inhibition of nitric oxide synthase

“…IC50 for 7-NI against rat cerebellar NOS of 700 nM; Moore et al, 1993a,b) and (ii) 7-NI-induced antinociception is at least partially reversible with L-arginine (Moore et al, 1993b) which did not influence the response to 7-NI in the present study. As yet we cannot rule out the possibility that a combined effect, for example, on glutamate-induced Ca2+ influx into nociresponsive neurones in the dorsal spinal cord coupled with inhibition of NOS enzyme activity in these same neurones may jointly contribute to the antinociceptive effect of 7-NI.…”

Characterization of nitric oxide synthase activity in sheep urinary tract: functional implications

“…Since the kinetic constants reported here are stimated at a single long time point (60 min of incubation), our results will not account for the possibility of a slow inhibition process such as that described for L-NOARG and L-NMMA (Komori et al, 1994). Unexpectedly, 7-nitroindazole, reported to be a selective inhibitor of nNOS (Moore et al, 1993), showed a weak effect on NOS activity in the urethra and detrusor with Ki values around 25 gM. However, it has been shown that inhibition of nNOS by 7-nitroindazole was competitive vs L-arginine and vs BH4.…”

“…It appears that constitutive enzymes (nNOS and eNOS) are more sensitive to inhibition by L-NOARG and L-NAME than the inducible enzyme (iNOS), which, in turn, seems to be effectively inhibited by L-NMMA rather than by L-NOARG (Komori et al, 1994). Another structural analgoue of L-arginine, L-canavanine, shows some selectivity towards iNOS (McCall et al, 1989), while the fused heterocyclic 7-nitroindazole has been described as a selective inhibitor for nNOS (Moore et al, 1993). Our results show that NOS activity in both urethra and detrusor is strongly inhibited by L-NOARG and L-NAME, less inhibited by L-NMMA, while 7-NI was a weak inhibitor and Lcanavanine had no effect.…”

Inhibition of Vascular Nitric Oxide after Rat Chronic Brain Hypoperfusion: Spatial Memory and Immunocytochemical Changes

“…The doses were chosen from previous trials to achieve temporary inhibition of each NOS isoform (Jiang et al, 2002;Wolff et al, 1998;Zhu et al, 2003;Escott et al, 1998;Moore et al, 1993).…”