Role of adenosine receptors in the anti-nociceptive effects of allopurinol in mice.

BACKGROUND: Inhibition of xanthine oxidase by allopurinol increases hypoxanthine and xanthine, which are converted to purines, including the inhibitory neuromodulator adenosine. AIM: We aimed to investigate the antinociceptive effects of allopurinol in thermal and chemical pain models in mice and to evaluate its possible antinociceptive mechanism by using selective adenosine receptors A1, A2A antagonists in mice. MATERIALS AND METHODS: Sixty four adult male mice were used. Mice received an intraperitoneal injection of vehicle or allopurinol (50-200 mg/kg). Assessment of antinociceptive effects and locomotor activity were performed in three models of acute pain; a thermal model and two chemical model. RESULTS: Allopurinol presented dose-dependent antinociceptive effects in all models with no obvious motor deficits. The opioid antagonist naloxone did not reverse these effects. The selective A1 antagonist, DPCPX, and the selective A2A antagonist, ZM241385, completely prevented allopurinol-induced antinociception. CONCLUSIONS: Allopurinol-induced antinociception may be related to adenosine accumulation. Allopurinol seems to be well tolerated with no locomotor side effects at high doses and it may be useful to treat pain syndromes.

Respiratory and postprandial changes in portal flow rate: assessment by phase contrast MR imaging.

The objective of this study was to investigate the variability of several different phase contrast (PC) magnetic resonance techniques and duplex Doppler imaging (DDI) for measuring portal flow rate (PFR) with different patterns of respiration before and after a standard meal. PFR was measured in nine normal volunteers in both fasting and postprandial states, using both 2D and cine PC MR techniques. Two-dimensional PC technique was performed with and without breath-hold (BH). Four different patterns of BH (relaxed maximal inspiration, expiration, Valsalva maneuver, and Müller or reversed Valsalva) were used. Cine PC technique was performed without BH. DDI measurement of PFR was done in the fasting state with relaxed inspiration. PFR measurements made by means of PC MR techniques varied, depending on BH method, and were systematically less than those obtained by DDI. PFR measured during inspiration was significantly less than that measured during expiration and other respiratory maneuvers (P < .03). PFR increased significantly after a meal for PC and Doppler measurements, with a range of mean increases of 24 to 74%. Two-dimensional PC MR imaging techniques yielded differing measurements of PFR, depending on whether they were done with or without BH, as well as on the pattern of BH. PC mean measures of PFR were consistently less than those of DDI. The physiologic inspiratory decreases and postprandial increases of the PFR were evident from 2D and cine PC MRI techniques, as well as with DDI.