Browsing by Author "Iturriaga R."

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    Acute Chemogenetic Inhibition of Caudal NTS Astrocytes Reduced Systemic Blood Pressure in Rats Exposed to Chronic Intermittent Hypoxia-mimicking Sleep Apnea Syndrome
    (NLM (Medline), 2022) Iturriaga R.; Toledo C.; Ortolani D.; Del Rio R.
    © FASEB.Chronic intermittent hypoxia (CIH), the main feature of obstructive sleep apnea, enhances carotid body (CB) discharges, leading to heightened sympathetic outflow and systemic hypertension. Previously, we found that CBs play a pivotal role in the hyperactivation of central nervous system (CNS) autonomic nuclei following CIH, particularly at the level of the caudal portion of the nucleus of the tractus solitary (NTS). Indeed, increased CB afferent activity during CIH increases the expression of pro-inflammatory cytokines in the NTS, suggesting that CBs may drive neuroinflammation at key cardiorespiratory regulatory areas. Astrocytes has been implicated in inflammatory processes at the CNS. However, the contribution of NTS astrocytes on the cardiorespiratory abnormalities following CIH has not been studied. Accordingly, we assessed the role of astrocytes residing within the NTS on the maintenance of hypertension following CIH. Male Sprague-Dawley rats (200 g) were exposed to CIH (5-6% inspired O2 for 20s, followed by room air for 280s, 12 times/h, 8 h/day, for 28 days). Arterial blood pressure (BP) was measured by indwelling telemetry. At 7 days of CIH exposure, rats were anesthetized and an adeno-associated virus (AAV; 450 nL, 1*10-12 vg) containing an inhibitory (Gi) Designer Receptor Exclusively Activated by Designer Drugs (DREADD) expressed under the control of the GFAP promoter was bilaterally injected into the caudal portion of the NTS using stereotaxic coordinates (-14.3 mm to bregma). At day 28 of CIH, hemodynamic and respiratory parameters were recorded before and after inhibition of NTS astrocytes with clozapine N-oxide (CNO, 1mg/kg, ip.). At the end of the experiments rats were transcardially perfused with 4% buffered paraformaldehyde, brains extracted and sectioned to assess astrocyte activation within the NTS. Twenty-eight days of CIH resulted in a significant 2-fold increase in NTS astrocyte activation as evidenced by enhanced reactivity of GFAP. Additionally, resting BP was markedly elevated compared to Sham conditions (MABP, 98±2 vs. 84±2 mmHg, CIH vs. Sham; p<0.05). Acute chemogenetic inhibition of NTS astrocytes following 28 days of CIH results in a significant reduction in BP (⁓10 mmHg; p<0.05). In addition, the exacerbated hemodynamic response triggered by acute hypoxic stimulation (Fi O2 10%) in rats exposed to CIH for 28 days was also reduced by NTS astrocyte inhibition ΔMABP, 30±2 vs. 15±2 mmHg, pre vs. post CNO; p<0.05). No cardiovascular effects of CNO alone were found in control rats that did not underwent AAV-DREADD-Gi injection into the NTS. Taken together, our results support a role for NTS astrocyte activation on the maintenance of hypertension following chronic CIH and suggest that activation of NTS astrocytes may participate in the CB-mediated cardiovascular reflex response during hypoxic stimulation.
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    Blockade of Stim-activated TRPC-ORAI Channels Prevents Vascular Remodeling and Pulmonary Hypertension Induced by Chronic Intermittent Hypoxia
    (NLM (Medline), 2022) Castillo-Galan S.; Iturriaga R.; Riquelme B.
    © FASEB.Obstructive sleep apnea (OSA), a sleep breathing disorder featured by chronic intermittent hypoxia (CIH), is associate with mild pulmonary hypertension (PH). Rats exposed to CIH developed pulmonary vascular remodeling and PH, but the pathogenic mechanisms are not well known. In addition, CIH overexpressed Stim-activated TRPC-ORAI channels (STOC) in the lung, which paralleled the increase of right systolic ventricle pressure (RVSP) and pulmonary vascular remodeling. Accordingly, we tested weater a treatment with the STOC bloker 2-Aminoethyl diphenylborinate (2-APB), started from day 14 days to exposure to CIH may reduce vascular remodelling and PH. Male Sprague-Dawley rats (~200g) were exposed CIH (5% O2, 12 times/h for 8h). At 14 days, osmotic pumps containing 2-APB (10 mg/kg/day, n=7) or its vehicle (n=7) were implanted, and rats were keep in CIH for 2 more weeks. At the end of CIH exposure, RVSP was measured in urethane-chloralose anesthetized rats. Animals were euthanized and lungs were removed to determine vascular remodeling and mRNA levels of the STOC forming subunits TRPC1, TRPC4, TRPC6, ORAI 1 and ORAI 2 by qPCR. CIH-treated rats were compared with aged-matched normoxic controls. 2-APB reduced the increase of RVSP (24.7 ± 1.6 vs. 36.5 ± 1.1 mmHg, 2-APB vs vehicle, respectively, p < 0.05) and the medial layer thickness of arteries (50-300 µm) (43.4 ± 1.1 vs. 66.5 ± 2.9 %, 2-APB vs vehicle, respectively, p < 0.05). In addition, 2-APB prevented the increase of α-actin-ir (8.8 ± 0.4 vs. 14.3 ± 0.6 pixels/μm2 , 2-APB and vehicle respectively, p < 0.05), and to KI67 positive cells (3.9 ± 0.8 vs. 6.3 ± 1.1 %, 2-APB and vehicle, respectively, p < 0.05). In addition, 2-APB treatment reverted the increased mRNA levels of TRPC1, TRPC4 and TRPC6, but induced an overexpression of ORAI 1, while ORAI 2 remained unchanged. The present results show that 2-APB treatment prevented the vascular pulmonary alterations induced by CIH, suggesting that the blockade of STOC may potentially be used to treat the pulmonary hypertension induced by OSA.
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    Carotid body chemoreceptors: physiology, pathology, and implications for health and disease
    (NLM (Medline), 2021) Iturriaga R.; Alcayaga J.; Chapleau M.W.; Somers V.K.
    The carotid body (CB) is the main peripheral chemoreceptor for arterial respiratory gases O2 and CO2 and pH, eliciting reflex ventilatory, cardiovascular, and humoral responses to maintain homeostasis. This review examines the fundamental biology underlying CB chemoreceptor function, its contribution to integrated physiological responses, and its role in maintaining health and potentiating disease. Emphasis is placed on 1) transduction mechanisms in chemoreceptor (type I) cells, highlighting the role played by the hypoxic inhibition of O2-dependent K+ channels and mitochondrial oxidative metabolism, and their modification by intracellular molecules and other ion channels; 2) synaptic mechanisms linking type I cells and petrosal nerve terminals, focusing on the role played by the main proposed transmitters and modulatory gases, and the participation of glial cells in regulation of the chemosensory process; 3) integrated reflex responses to CB activation, emphasizing that the responses differ dramatically depending on the nature of the physiological, pathological, or environmental challenges, and the interactions of the chemoreceptor reflex with other reflexes in optimizing oxygen delivery to the tissues; and 4) the contribution of enhanced CB chemosensory discharge to autonomic and cardiorespiratory pathophysiology in obstructive sleep apnea, congestive heart failure, resistant hypertension, and metabolic diseases and how modulation of enhanced CB reactivity in disease conditions may attenuate pathophysiology.
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    The Action of 2-Aminoethyldiphenyl Borinate on the Pulmonary Arterial Hypertension and Remodeling of High-Altitude Hypoxemic Lambs
    (Frontiers Media S.A., 2021) Castillo-Galan S.; Iturriaga R.; Parrau D.; Hernandez I.; Ebensperger G.; Herrera E.A.; Llanos A.J.; Reyes R.V.; Quezada S.; Diaz M.; Ebensperger G.; Herrera E.A.; Llanos A.J.; Reyes R.V.; Moraga F.A.; Iturriaga R.
    Copyright © 2022 Castillo-Galán, Parrau, Hernández, Quezada, Díaz, Ebensperger, Herrera, Moraga, Iturriaga, Llanos and Reyes.Calcium signaling is key for the contraction, differentiation, and proliferation of pulmonary arterial smooth muscle cells. Furthermore, calcium influx through store-operated channels (SOCs) is particularly important in the vasoconstrictor response to hypoxia. Previously, we found a decrease in pulmonary hypertension and remodeling in normoxic newborn lambs partially gestated under chronic hypoxia, when treated with 2-aminoethyldiphenyl borinate (2-APB), a non-specific SOC blocker. However, the effects of 2-APB are unknown in neonates completely gestated, born, and raised under environmental hypoxia. Accordingly, we studied the effects of 2-APB-treatment on the cardiopulmonary variables in lambs under chronic hypobaric hypoxia. Experiments were done in nine newborn lambs gestated, born, and raised in high altitude (3,600 m): five animals were treated with 2-APB [intravenous (i.v.) 10 mg kg–1] for 10 days, while other four animals received vehicle. During the treatment, cardiopulmonary variables were measured daily, and these were also evaluated during an acute episode of superimposed hypoxia, 1 day after the end of the treatment. Furthermore, pulmonary vascular remodeling was assessed by histological analysis 2 days after the end of the treatment. Basal cardiac output and mean systemic arterial pressure (SAP) and resistance from 2-APB- and vehicle-treated lambs did not differ along with the treatment. Mean pulmonary arterial pressure (mPAP) decreased after the first day of 2-APB treatment and remained lower than the vehicle-treated group until the third day, and during the fifth, sixth, and ninth day of treatment. The net mPAP increase in response to acute hypoxia did not change, but the pressure area under the curve (AUC) during hypoxia was slightly lower in 2-APB-treated lambs than in vehicle-treated lambs. Moreover, the 2-APB treatment decreased the pulmonary arterial wall thickness and the α-actin immunoreactivity and increased the luminal area with no changes in the vascular density. Our findings show that 2-APB treatment partially reduced the contractile hypoxic response and reverted the pulmonary vascular remodeling, but this is not enough to normalize the pulmonary hemodynamics in chronically hypoxic newborn lambs.