resiniferatoxin and Hypertension

Hypertension is associated with increased sympathetic activity. A component of this sympathoexcitation may be driven by increased signaling from sensory endings from the heart to the autonomic control areas in the brain. This pathway mediates the so-called cardiac sympathetic afferent reflex, which is also activated by coronary ischemia or other nociceptive stimuli in the heart. The cardiac sympathetic afferent reflex has been shown to be enhanced in the heart failure state and in renal hypertension. However, little is known about its role in the development or progression of hypertension or the phenotype of the sensory endings involved. To investigate this, we used the selective afferent neurotoxin, resiniferatoxin (RTX) to chronically abolish the cardiac sympathetic afferent reflex in 2 models of hypertension; the spontaneous hypertensive rats (SHRs) and AngII (angiotensin II) infusion (240 ng/kg per min). Blood pressure (BP) was measured in conscious animals for 2 to 8 weeks post-RTX. Epidural application of RTX to the T1-T4 spinal segments prevented the further BP increase in 8-week-old SHR and lowered BP in 16-week-old SHR. RTX did not affect BP in Wistar-Kyoto normotensive rats nor in AngII-infused rats. Epicardial application of RTX (50 µg/mL) in 4-week-old SHR prevented the BP increase whereas this treatment does not lower BP in 16-week-old SHR. When RTX was administered into the L2-L5 spinal segments of 16-week-old SHR, no change in BP was observed. These findings indicate that signaling via thoracic afferent nerve fibers may contribute to the hypertension phenotype in the SHR but not in the Ang II infusion model of hypertension.

Topics: Angiotensin II; Animals; Arterial Pressure; Blood Pressure; Diterpenes; Ganglia, Spinal; Heart; Heart Rate; Hypertension; Male; Neurotoxins; Rats; Rats, Inbred SHR; Rats, Sprague-Dawley; Reflex; Sympathetic Nervous System; TRPV Cation Channels

Our previous studies showed that pro-inflammatory cytokines (PIC) in the hypothalamic paraventricular nucleus (PVH) potentiated the cardiac sympathetic afferent reflex (CSAR) in normotensive rats. This study determined whether PIC in the PVH mediate enhanced CSAR and over-excited sympathetic activity in spontaneously hypertensive rats (SHR). CSAR was evaluated by renal sympathetic nerve activity (RSNA) response to epicardial application of bradykinin (BK). Inflammatory cytokine levels were measured with ELISA. In both SHR and normotensive Wistar-Kyoto (WKY) rats, PVH microinjection of PIC, tumour necrosis factor (TNF)-α or interleukin (IL)-1β, increased the baseline mean arterial blood pressure (MAP), RSNA and the CSAR, but anti-inflammatory cytokines (AIC), IL-4 or IL-13, only increased the baseline MAP. PVH pretreatment with PIC caused sub-response dose of angiotension (Ang) II to produce baseline RSNA and MAP elevation and the CSAR enhancement responses, but AIC (IL-4 or IL-13) did not. PVH microinjection of PIC induced greater changes in SHR than in normotensive WKY rats. In addition, stimulation of cardiac sympathetic afferents with epicardial application of BK increased PIC levels in the PVH in both SHR and WKY rats. Intrapericardial administration of resiniferatoxin (RTX) which abolished the CSAR decreased the PIC levels in the PVH to a lower level in SHR than in WKY rats. These results suggest that the increased PIC in the PVH in SHR mediated the increased sympathetic outflow and the enhanced CSAR, and that the augmented effect of Ang II in the PVH on sympathetic activity and the CSAR is also associated with PIC.

Topics: Angiotensin II; Animals; Arterial Pressure; Bradykinin; Calcium Channel Agonists; Cytokines; Diterpenes; Hypertension; Interleukin-13; Interleukin-1beta; Interleukin-4; Kidney; Male; Paraventricular Hypothalamic Nucleus; Random Allocation; Rats, Inbred SHR; Rats, Inbred WKY; Reflex; Sympathetic Nervous System; Tumor Necrosis Factor-alpha

We recently found that adipose afferent reflex (AAR) induced by chemical stimulation of white adipose tissue (WAT) increased sympathetic outflow and blood pressure in normal rats. The study was designed to test the hypothesis that AAR contributes to sympathetic activation in obesity hypertension. Male rats were fed with a control diet (12% kcal as fat) or high-fat diet (42% kcal as fat) for 12 weeks to induce obesity hypertension. Stimulation of WAT with capsaicin increased renal sympathetic nerve activity and mean arterial pressure. Both AAR and WAT afferent activity were enhanced in obesity hypertension (OH) compared with obesity nonhypertension (ON) and in ON compared with obesity-resistant or control diet rats. WAT sensory denervation induced by resiniferatoxin caused greater decreases in renal sympathetic nerve activity and mean arterial pressure in OH than ON and in ON than obesity-resistant or control. The depressor effect of resiniferatoxin lasted ≥ 3 weeks in OH. Leptin antagonist in WAT reduced renal sympathetic nerve activity and mean arterial pressure in OH. WAT injection of capsaicin increased plasma renin, angiotensin II, and norepinephrine levels in OH and caused more c-fos expression in paraventricular nucleus in OH than ON and in ON than obesity-resistant or control rats. Inhibiting paraventricular nucleus neurons with lidocaine attenuated renal sympathetic nerve activity in OH and ON, decreased mean arterial pressure in OH, and abolished the capsaicin-induced AAR in all groups. The results indicate that enhanced AAR contributes to sympathetic activation in OH, and paraventricular nucleus plays an important role in the enhanced AAR and sympathetic activation in OH.

Topics: Adipose Tissue, White; Angiotensin II; Animals; Blood Pressure; Capsaicin; Diet, High-Fat; Diterpenes; Enzyme-Linked Immunosorbent Assay; Hypertension; Immunohistochemistry; Lidocaine; Male; Norepinephrine; Obesity; Paraventricular Hypothalamic Nucleus; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Reflex; Renin; Sensory System Agents; Sympathetic Nervous System

The attenuation of baroreflex gain associated with hereditary hypertension could involve abnormal signalling by nitric oxide or substance P. Baroreflex gain was measured in age-matched male genetically hypertensive (GH) and nonnotensive (N) anaesthetised rats from heart rate changes in response to i.v. phenylephrine or sodium nitroprusside. In subgroups of these animals, nitric oxide synthesis was inhibited using NG-nitro-L-arginine methyl ester (L-NAME, 30 mg x kg(-1) i.v.), substance P transmission was blocked using the antagonist SR 140333 (360 nmoles x kg(-1) i.v.) or substance P release was inhibited with resiniferatoxin (4 doses of 0.3 microg x kg(-1) i.v. at 4 min intervals). Baroreflex gain was markedly reduced in GH compared to N animals (N -0.37 +/- 0.04 beat x min(-1) x mm Hg(-1), GH -0.17 +/- 0.02 beat x min(-1) x mm Hg(-1), p < 0.0001). Inhibition of nitric oxide synthase increased baroreflex gain in each strain, but the inter-strain difference in gain persisted (post-treatment N -0.57 +/- 0.07 beat x min(-1) x mm Hg(-1), GH -0.24 +/- 0.05 beat x min(-1) x mm Hg(-1) (p < 0.001). Blockade of receptors or inhibition of substance P release did not affect gain in either strain. Nitric oxide, but not substance P, appears to play an inhibitory role in the rat arterial baroreflex. Impairment of baroreflex gain in GH rats is not secondary to altered nitric oxide signaling.

Topics: Animals; Baroreflex; Blood Pressure; Diterpenes; Enzyme Inhibitors; Heart Rate; Hypertension; Male; Neurokinin-1 Receptor Antagonists; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Nitroprusside; Phenylephrine; Piperidines; Quinuclidines; Rats; Rats, Inbred SHR; Rest; Substance P; Vasoconstrictor Agents; Vasodilator Agents

The airways of the genetically hypertensive rat (GH) are hyperinnervated by substance P-containing sensory nerves and exhibit reduced inflammatory responsiveness to substance P and to capsaicin. The present study measured tracheal inflammation to resiniferatoxin (1.0 microgram/kg i.v.), a capsaicin analogue, which lacks the hypotensive action of capsaicin itself, alone or after the neuronal nitric oxide synthase inhibitor 1-(2-trifluoromethylphenyl)imidazole (TRIM) (50 mg/kg i.p.). The inflammatory response to resiniferatoxin alone was 50% lower in untreated GH than in control rats, a similar strain difference to that seen previously with capsaicin. Pre-treatment with TRIM had no effect on inflammation in either strain. Binding kinetics of the tachykinin NK(1) receptor antagonist [3H](S)-1-(2-[3-(3, 4-dichlorophenyl)-1-(3-isopropoxyphenylacetyl)piperidin-3-yl]ethyl)-4- phenyl-l-azoniabicyclo[2,2,2,]octane chloride ([3H]SR140333)(0.125-16.0 nM) showed 50% reduction of B(max) in GH versus control tracheae (74+/-13 cf.165+/-26 fmol/mg protein). Our results indicate that the reduced neurogenic inflammatory responsiveness in GH rats can be attributed entirely to reduced tachykinin NK(1) receptor numbers.

Topics: Animals; Binding, Competitive; Capillary Permeability; Diterpenes; Hypertension; Inflammation; Male; Membranes; Piperidines; Quinuclidines; Radioligand Assay; Rats; Rats, Inbred Strains; Receptors, Neurokinin-1; Spinal Cord; Substance P; Trachea; Tritium