Mechanisms involved in the antinociception induced by systemic administration of guanosine in mice

Abstract

Background and purpose: It is well known that adenine-based purines exert multiple effects on pain transmission. However, less attention has been given to the potential effects of guanine-based purines on pain transmission. The aim of this study was to investigate the effects of intraperitoneal (i.p.) and oral (p.o.) administration of guanosine on mice pain models. Additionally, investigation into the mechanisms of action of guanosine, its potential toxicity and cerebrospinal fluid (CSF) purine levels were also assessed.

Experimental approach: Mice received an i.p. or p.o. administration of vehicle (0.1 mM NaOH) or guanosine (up to 240 mg x kg(-1)) and were evaluated in several pain models.

Key results: Guanosine produced dose-dependent antinociceptive effects in the hot-plate, glutamate, capsaicin, formalin and acetic acid models, but it was ineffective in the tail-flick test. Additionally, guanosine produced a significant inhibition of biting behaviour induced by i.t. injection of glutamate, AMPA, kainate and trans-ACPD, but not against NMDA, substance P or capsaicin. The antinociceptive effects of guanosine were prevented by selective and non-selective adenosine receptor antagonists. Systemic administration of guanosine (120 mg x kg(-1)) induced an approximately sevenfold increase on CSF guanosine levels. Guanosine prevented the increase on spinal cord glutamate uptake induced by intraplantar capsaicin.

Conclusions and implications: This study provides new evidence on the mechanism of action of the antinociceptive effects after systemic administration of guanosine. These effects seem to be related to the modulation of adenosine A(1) and A(2A) receptors and non-NMDA glutamate receptors.

Figure 1

Effects of i.p. (A) or p.o. (B) administration of vehicle (0.1 mN NaOH), morphine (Mor – 6 mg·kg⁻¹) or guanosine (7.5 to 240 mg·kg⁻¹) in the i.pl. capsaicin test in mice. Columns represent mean time spent in licking the injected hindpaw, and vertical bars represent SEM. n= 8–10. *P < 0.05, **P < 0.01 and ***P < 0.001 compared with vehicle, one-way anova /Student–Newman–Keuls.

Figure 2

Effects of i.p. administration of vehicle (0.1 mN NaOH), morphine (Mor – 6 mg·kg⁻¹) or guanosine (30, 60 or 120 mg·kg⁻¹) in the tail-flick (A), hot-plate (B), i.pl. glutamate (C), i.p. acetic acid (D), and formalin (E-neurogenic phase and F-inflammatory phase) tests in mice. Dexamethasone (Dexa – 30 mg·kg⁻¹) was also administered in the formalin test. (A and B) Columns represent mean percent of maximum possible effect (% MPE), and vertical bars represent SEM. (C–F) Columns represent mean time spent in licking the injected hindpaw, and vertical bars represent SEM. n= 8–10. *P < 0.05, **P < 0.01 and ***P < 0.001 compared with vehicle, one-way anova /Student–Newman–Keuls.

Figure 3

Effects of p.o. administration of vehicle (0.1 mN NaOH), morphine (Mor – 6 mg·kg⁻¹) or guanosine (30, 60 or 120 mg·kg⁻¹) in the tail-flick (A), hot-plate (B), i.pl. glutamate (C), i.p. acetic acid (D), and formalin (E-neurogenic phase and F-inflammatory phase) tests in mice. Dexamethasone (Dexa – 30 mg·kg⁻¹) was also administered in the formalin test. (A and B) Columns represent mean percent of maximum possible effect (% MPE), and vertical bars represent SEM. (C–F) Columns represent mean time spent licking the injected hindpaw, and vertical bars represent SEM. n= 8–10. *P < 0.05, **P < 0.01 and ***P < 0.001 compared with vehicle, one-way anova /Student–Newman–Keuls. MPE, maximum possible effect.

Figure 4

Effects of i.p. vehicle (0.1 mN NaOH) or guanosine (30, 60 or 120 mg·kg⁻¹) in the glutamate (A, 175 nmol per site, i.t.)-, AMPA (B, 135 pmol per site, i.t.)-, kainate (C, 110 pmol per site, i.t.)-, trans-ACPD (D, 50 nmol per site, i.t.)-, NMDA (E, 450 pmol per site, i.t.)-, substance P (F, 135 ng per site, i.t.)- or capsaicin (G, 30 ng per site, i.t.)-induced biting in mice. Columns represent mean, and vertical bars represent SEM. n= 8–10. *P < 0.05, **P < 0.01 and ***P < 0.001 compared with vehicle, one-way anova /Student–Newman–Keuls. AMPA, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid; NMDA, N-methyl-D-aspartate.

Figure 5

Effects of caffeine (10 mg·kg⁻¹, i.p., A), DPCPX (1 mg·kg⁻¹, i.p., B) or SCH58261 (0.5 mg·kg⁻¹, i.p., B) 15 min before vehicle (0.1 mN NaOH), adenosine (100 mg·kg⁻¹, i.p.) or guanosine (60 mg·kg⁻¹, i.p.) in the i.pl. capsaicin test in mice. Columns represent mean time spent in licking the injected hindpaw, and vertical bars represent SEM. n= 14–18. ***P < 0.001 compared with vehicle, one-way anova /Student–Newman–Keuls. DPCPX, 8-cyclopentyl-1,3-dipropylxanthine; SCH58261, 5-amino-2-(2-furyl)-7-phenylethyl-pyra-zolo-[4,3-e]-1,2,4-triazolo[1,5c]pyrimidine.

Figure 6

Effects of L-arginine (600 mg·kg⁻¹, i.p.) 20 min before L-NOARG (75 mg·kg⁻¹, i.p.), vehicle (0.1 mN NaOH) or guanosine (60 mg·kg⁻¹, i.p.) in the i.pl. glutamate-induced nociception (A). Effects of L-NOARG (30 mg·kg⁻¹, i.p.), methylene blue (1 mg·kg⁻¹, i.p.) or vehicle (saline, i.p.) 15 min before guanosine (60 mg·kg⁻¹, i.p.) or vehicle (0.1 mN NaOH, i.p.) (B). The total time spent in licking the hindpaw was measured for 15 min after i.pl. injection of glutamate. Columns represent mean, and vertical bars represent SEM. n= 8–10. *P < 0.05 and **P < 0.01 compared with vehicle, one-way anova /Student–Newman–Keuls. L-NOARG, N-nitro-L-arginine.

Figure 7

Effects of i.p. vehicle (0.1 mN NaOH) or guanosine (30, 60 or 120 mg·kg⁻¹) in the i.pl. glutamate-induced paw oedema in mice (A). Effects of i.pl. administration of vehicle (0.1 mN NaOH) or guanosine (100, 200, 400 nmol) against i.pl. glutamate-induced paw oedema in mice (B). Columns represent mean weight difference (injected–non-injected paw), and vertical bars represent SEM. n= 8. **P < 0.01 compared with vehicle, one-way anova /Student–Newman–Keuls.

Figure 8

Effects of i.p. (A) or p.o. (B) vehicle (0.1 mN NaOH) or guanosine (30, 60 or 120 mg·kg⁻¹) on CSF purine concentration. The columns represent mean (µM), and vertical bars represent SEM. n= 8. **P < 0.01 and ***P < 0.001 compared with vehicle, one-way anova /Student–Newman–Keuls. CSF, cerebrospinal fluid.

Figure 9

Effects of i.p. guanosine and i.pl. capsaicin on glutamate uptake by mice cortical (A), and spinal cord (B) slices. Mice were treated with an i.p. injection of vehicle (0.1 mN NaOH) or guanosine (60 mg·kg⁻¹); after 30 min, animals received an i.pl. injection of vehicle (DMSO 5%) or capsaicin. After behavioural evaluation, the mice were killed and the cortical and spinal cord slices processed for glutamate uptake assay. Data are mean ± SEM. n= 12. *P < 0.05 compared with vehicle, one-way anova /Student–Newman–Keuls. DMSO, dimethyl sulfoxide.

Figure 10

Effects of i.p. vehicle (0.1 mN NaOH) or guanosine (60 to 960 mg·kg⁻¹) on serum levels of creatinine (A), urea (B), aspartate aminotransferase (AST – C), and alanine aminotransferase (ALT – D) in mice. Mice received an i.p. injection of vehicle or guanosine 72 h before blood sampling. Data are mean ± SEM. n= 8. **P < 0.01 and ***P < 0.001 compared with vehicle, one-way anova /Student–Newman–Keuls. AST, aspartate aminotransferase.