Daniela Patinha

MICROINJECTION OF ANGIOTENSIN II IN THE CAUDAL VENTROLATERAL MEDULLA INDUCES HYPERALGESIA

Nociceptive transmission from the spinal cord is controlled by supraspinal pain modulating systems that include the caudal ventrolateral medulla (CVLM). The neuropeptide angiotensin II (Ang II) has multiple effects in the CNS and at the medulla oblongata. Here we evaluated the expression of angiotensin type 1 (AT(1)) receptors in spinally-projecting CVLM neurons, and tested the effect of direct application of exogenous Ang II in the CVLM on nociceptive behaviors. Although AT(1)-immunoreactive neurons occurred in the CVLM, only 3% of AT(1)-positive neurons were found to project to the dorsal horn, using double-immunodetection of the retrograde tracer cholera toxin subunit B. In behavioral studies, administration of Ang II (100 pmol) in the CVLM gave rise to hyperalgesia in both the tail-flick and formalin tests. This hyperalgesia was significantly attenuated by local administration of the AT(1) antagonist losartan. The present study demonstrates that Ang II can act on AT(1) receptors in the CVLM to modulate nociception. The effect on spinal nociceptive processing is likely indirect, since few AT(1)-expressing CVLM neurons were found to project to the spinal cord. The renin-angiotensin system may also play a role in other supraspinal areas implicated in pain modulation.

Role of H2O2 in hypertension, renin‐angiotensin system activation and renal medullary disfunction caused by angiotensin II

BACKGROUND AND PURPOSE Activation of the intrarenal renin‐angiotensin system (RAS) and increased renal medullary hydrogen peroxide (H2O2) contribute to hypertension. We examined whether H2O2 mediated hypertension and intrarenal RAS activation induced by angiotensin II (Ang II).

Angiotensin II contributes to glomerular hyperfiltration in diabetic rats independently of adenosine type I receptors.

Increased angiotensin II (ANG II) or adenosine can potentiate each other in the regulation of renal hemodynamics and tubular function. Diabetes is characterized by hyperfiltration, yet the roles of ANG II and adenosine receptors for controlling baseline renal blood flow (RBF) or tubular Na(+) handling in diabetes is presently unknown. Accordingly, the changes in their functions were investigated in control and 2-wk streptozotocin-diabetic rats after intrarenal infusion of the ANG II AT1 receptor antagonist candesartan, the adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), or their combination. Compared with controls, the baseline blood pressure, RBF, and renal vascular resistance (RVR) were similar in diabetics, whereas the glomerular filtration rate (GFR) and filtration fraction (FF) were increased. Candesartan, DPCPX, or the combination increased RBF and decreased RVR similarly in all groups. In controls, the GFR was increased by DPCPX, but in diabetics, it was decreased by candesartan. The FF was decreased by candesartan and DPCPX, independently. DPCPX caused the most pronounced increase in fractional Na(+) excretion in both controls and diabetics, whereas candesartan or the combination only affected fractional Li(+) excretion in diabetics. These results suggest that RBF, via a unifying mechanism, and tubular function are under strict tonic control of both ANG II and adenosine in both control and diabetic kidneys. Furthermore, increased vascular AT1 receptor activity is a contribution to diabetes-induced hyperfiltration independent of any effect of adenosine A1 receptors.

Diabetes-induced increase of renal medullary hydrogen peroxide and urinary angiotensinogen is similar in normotensive and hypertensive rats

AIMS Activation of renal renin-angiotensin system (RAS) and reactive oxygen species (ROS) are the main pathophysiological mechanisms associated with kidney injury both in diabetes and hypertension. However, the contribution to medullary damage when the two pathologies coexist has seldom been explored. MAIN METHODS Diabetes was induced with streptozotocin in twelve week-old male Wistar and spontaneously hypertensive rats (SHR) rats; controls received vehicle. Three weeks later, systolic blood pressure (SBP), plasma and urinary angiotensinogen (AGT), renal oxidative stress and metabolic status were evaluated. KEY FINDINGS SBP was higher in SHR-controls than in Wistar-controls (200±6 and 127±3mmHg, respectively) and decreased in SHR-diabetics but not in Wistar-diabetics (143±8 and 122±6mmHg, respectively). Renal medullary hydrogen peroxide (H2O2) production was similarly increased in diabetics (Wistar: 0.32±0.04 and 1.11±0.10nmol/mg protein, respectively; SHR: 0.40±0.05 and 0.90±0.14nmol/mg protein, respectively) and positively correlated with glycemia (Wistar: r=0.7166, SHR: r=0.7899, p<0.05) and urinary AGT excretion (Wistar: r=0.8333; SHR: r=0.8326, p<0.05). Cortical H2O2 production was higher in SHR-controls than in Wistar-controls (1.10±0.09 and 0.26±0.04nmol/mg protein, respectively) and diabetes induction decreased it in SHR (0.70±0.09nmol/mg protein). Diabetes increased urinary AGT excretion by more than 7-fold and decreased plasma AGT concentration by more than 1.5-fold in both strains. SIGNIFICANCE Our results show that STZ-induced diabetes increases medullary H2O2 production and urinary AGT excretion with similar magnitude in normotensive and hypertensive animals. Reducing blood pressure attenuates hypertension-associated cortical damage but does not prevent medullary dysfunction.

Activation of adenosine receptors improves renal antioxidant status in diabetic Wistar but not SHR rats

Abstract Background. Diabetes and hypertension independently contribute to renal injury, and the major mechanisms involved are increased reactive oxygen species (ROS) bioavailability and renin-angiotensin system (RAS) activation. We investigated the role of adenosine in controlling ROS production and RAS activation associated with renal dysfunction in hypertension and diabetes. Methods. Fourteen days after induction of diabetes with streptozotocin in 12-week-old male Wistar and spontaneously hypertensive (SHR) rats, animals were treated during 7 days with 2-chloroadenosine (CADO group, 5 mg/kg/d), a stable analogue of adenosine, or underwent a sham operation procedure. At the end of the study (day 21), intra-arterial systolic blood pressure (SBP) was measured, and 24-h urine and plasma samples and renal tissue were collected. Results. CADO treatment decreased the plasma glucose concentration and glucose and protein excretion by more than 30% in both strains. CADO treatment decreased SBP in diabetic SHR rats (143 ± 8 versus 114 ± 4 mmHg, p < 0.05), but not in diabetic Wistar rats. The hypotensive effect of CADO was associated to a ∼70% increase in plasma angiotensinogen (AGT) concentration and a ∼50% decrease in urinary AGT excretion. CADO also caused a decrease in medullary and cortical hydrogen peroxide production of about 40%, which was associated with a proportional increase in glutathione peroxidase (GPx) activity in diabetic Wistar but not in diabetic SHR animals. Conclusions. These results suggest that activation of adenosine receptors improves renal antioxidant capacity in diabetic Wistar but not SHR rats, although it improves glucose metabolism in both strains. Furthermore, activation of adenosine receptors does not seem to be directly influencing AGT production.

393 ROLE OF ANGIOTENSIN II IN PAINFUL DIABETIC NEUROPATHY AND HYPERTENSION

Recognition memory was tested in a novel-object-recognition paradigm. Animals were killed by transcardiac perfusion and spinal cords were removed, sectioned and stained with FITC-conjugated isolectin B4 (IB4), a marker of primary afferent C-fibres. Sections were visualised using fluorescent microscopy. Results: IB4 staining was decreased in laminae 1–2 of the spinal cord on the ipsilateral side to ligation, compared with the contralateral side and with sham controls, which indicates the ligation was successful. SNL rats developed mechanical allodynia, and expressed thermal hyperalesia. SNL surgery had no effect on spatial learning in the acquisition phase of the MWM or on spatial memory assessed in both the MWM probe trial and the T-maze. Recognition memory was also unaffected in SNLs as compared with shams. Conclusions: SNL surgery modelled symptoms characteristic of neuropathic pain but was not associated with cognitive impairment under these experimental conditions.