Role of Angiotensin II type 1 receptor on renal NAD(P)H oxidase, oxidative stress and inflammation in nitric oxide inhibition induced-hypertension.

AIMS: Activation of the renin-angiotensin system (RAS), renal oxidative stress and inflammation are constantly present in experimental hypertension. Nitric oxide (NO) inhibition with N(w)-nitro-L-arginine methyl ester (L-NAME) has previously been reported to produce hypertension, increased expression of Angiotensin II (Ang II) and renal dysfunction. The use of Losartan, an Ang II type 1 receptor (AT1R) antagonist has proven to be effective reducing hypertension and renal damage; however, the mechanism by which AT1R blockade reduced kidney injury and normalizes blood pressure in this experimental model is still complete unknown. The current study was designed to test the hypothesis that AT1R activation promotes renal NAD(P)H oxidase up-regulation, oxidative stress and cytokine production during L-NAME induced-hypertension. MAIN METHODS: Male Sprague-Dawley rats were distributed in three groups: L-NAME, receiving 70 mg/100ml of L-NAME, L-NAME+Los, receiving 70 mg/100ml of L-NAME and 40 mg/kg/day of Losartan; and Controls, receiving water instead of L-NAME or L-NAME and Losartan. KEY FINDINGS: After two weeks, L-NAME induced high blood pressure, renal overexpression of AT1R, NAD(P)H oxidase sub-units gp91, p22 and p47, increased levels of oxidative stress, interleukin-6 (IL-6) and interleukin-17 (IL-17). Also, we found increased renal accumulation of lymphocytes and macrophages. Losartan treatment abolished the renal expression of gp91, p22, p47, oxidative stress and reduced NF-κB activation and IL-6 expression. SIGNIFICANCE: These findings indicate that NO induced-hypertension is associated with up-regulation of NADPH oxidase, oxidative stress production and overexpression of key inflammatory mediators. These events are associated with up-regulation of AT1R, as evidenced by their reversal with AT1R blocker treatment.

Opposite modulation of capsaicin-evoked substance P release by glutamate receptors.

Substance P and glutamate are present in primary afferent C-fibers and play important roles in persistent inflammatory and neuropathic pain. In the present study, we have examined whether activation of different glutamate receptor subtypes modulates the release of substance P evoked by the C-fiber selective stimulant capsaicin (1 microM) from rat trigeminal nucleus slices. The selective NMDA glutamate receptor agonist L-CCG-IV (1-10 microM) enhanced capsaicin-evoked substance P release about 100%. This facilitatory effect was blocked by 0.3 microM MK-801, a selective NMDA receptor antagonist. The metabotropic glutamate receptor agonists L-AP4 (group III) and DHPG (group I) (30-100 microM) inhibited capsaicin-evoked substance P release by approximately 60%. These inhibitory effects were blocked by the selective metabotropic glutamate receptor antagonist (+/-)-MCPG (5 microM). On the other hand, AMPA and kainate (0.1-10 microM), did not significantly affect capsaicin-evoked substance P release. Thus, substance P release from non-myelinated primary afferents, and possibly nociception, may be under the functional antagonistic control of some metabotropic and ionotropic glutamate receptor subtypes.

Dynorphin A increases substance P release from trigeminal primary afferent C-fibers.

Dynorphin A-(1-17) has been found to produce spinal antianalgesia and allodynia. Thus, we studied whether dynorphin A-(1-17) modulates substance P release evoked by the C-fiber-selective stimulant capsaicin (1 microM) from trigeminal nucleus caudalis slices. Very low concentrations of dynorphin A-(1-17) (0.01-0.1 nM) strongly facilitated capsaicin-evoked substance P release. This dynorphin A-(1-17) effect was not blocked by the opioid receptor antagonists naloxone (100 nM), beta-funaltrexamine (20 nM), naloxonazine (1 nM), nor-binaltorphimine (3 nM) and ICI 174,864 (N,N-dialyl-Tyr-Aib-Phe-Leu; 0.3 microM). Yet, the effect of dynorphin A-(1-17) was blocked by the NMDA receptor antagonist MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5-10-imine maleate; 0.3 microM). Neonatal treatment with capsaicin (50 mg/kg s.c.), which destroys substance P-containing primary afferents, abolished the excitatory effect of dynorphin A-(1-17) on K+-evoked substance P release. In conclusion, dynorphin A-(1-17) increases substance P release from C-fibers by the activation of NMDA receptors which supports the involvement of presynaptic mechanisms in dynorphin-induced antianalgesia and allodynia.

Multiphasic morphine modulation of substance P release from capsaicin-sensitive primary afferent fibers.

Morphine produces a multiphasic modulation of K+-evoked substance P release from trigeminal slices and dorsal root ganglion neurons in culture. We now found that the C-fiber stimulant, capsaicin (1 microM), evoked release of substance P that was inhibited, enhanced and inhibited by 0.1 nM, 1 microM, and 10 microM morphine, respectively. This morphine's multiphasic effect was blocked by naloxone (100 nM). Neonatal treatment with capsaicin produced thermal hypoalgesia and abolished the multiphasic effect of morphine on substance P release evoked by 50 mM K+. These findings suggest that the multiphasic modulation of substance P release by morphine is dependent on C-type afferents and may be of relevance to nociception.

Decrease in spontaneous motor activity and in brain lipid peroxidation in manganese and melatonin treated mice.

In the present study, we have evaluated whether melatonin (MEL) modulates Mn-induced decrease in spontaneous motor activity (SMA) and lipid peroxidation, estimated as malondialdehyde (MDA) formation, in several brain regions. In mice treated with manganese a decrease in SMA after 2 weeks of treatment was observed. In the group treated with Mn+MEL a significant greater reduction in SMA was detected at 4 weeks. MDA levels were reduced in both MEL and Mn treated mice. In the animals treated with MEL + Mn a higher reduction in MDA levels was observed. These results suggest that MEL modulates the effect of Mn on SMA and brain lipid peroxidation.