title: Alpha2-adrenoreceptor mediated sympathoinhibition of heart rate during acute hypoxia is diminished in conscious prostacyclin synthase deficient mice.
abstract: Acute hypoxia increases ventilatory drive in conscious animals, resulting in tachycardia. Sustained hypoxia changes the initial chemoreflex ventilatory increase to secondary ventilatory depression, which then evokes a gradual secondary heart rate (HR) reduction. Prostacyclin (PGI(2)) release is known to potentiate alpha(2)-adrenoreceptor (alpha(2)-AR) mediated inhibition of sympathoactivation during ischaemia and hypoxia. We examined whether alpha(2)-AR mediated sympathoinhibition was responsible for limiting hypoxic heart rate increases during initial sympathoactivation, and subsequent secondary HR depression, and if PGI(2) is required for sympathoinhibition of HR. The responses of unrestrained PGI(2) synthase deficient (PGID) and wild type (WT) mice to acute hypoxia (10% O(2) for 30 min) were investigated by simultaneous telemetry, whole body plethysmography and open-flow respirometry. PGID mice exhibited potentiated .V(E) (p < 0.007) after intraperitoneal vehicle injection (n = 8), but not so HR responses compared to WT mice during sustained hypoxia. Idazoxan (alpha(2)-AR antagonist, i.p. bolus 3 mg/kg) pretreatment did not change hypoxic ventilatory response in either group, but significantly elevated hypoxic HR in WT mice only (p < 0.013). Sodium meclofenamate (cyclooxygenase inhibition, i.p. bolus 25 mg/kg) pretreatment eliminated the potentiated .V(E) of PGID and caused significant basal hypotension that led to a transient hypertensive response to hypoxia. From these results, we suggest that alpha(2)-AR activation is required for coupling HR to central inspiratory drive during acute hypoxia, and that PGI(2) is required to enhance the inhibition of sympathoactivation.
authors.affiliation: Department of Cardiac Physiology, National Cardiovascular Center Research Institute, Suita-shi, Osaka 565-8565, Japan.
authors.forename: James T
authors.initials: JT
authors.lastname: Pearson
authors.forename: Mikiyasu
authors.initials: M
authors.lastname: Shirai
authors.forename: Chieko
authors.initials: C
authors.lastname: Yokoyama
authors.forename: Hirotsugu
authors.initials: H
authors.lastname: Tsuchimochi
authors.forename: Daryl O
authors.initials: DO
authors.lastname: Schwenke
authors.forename: Akito
authors.initials: A
authors.lastname: Shimouchi
authors.forename: Kenji
authors.initials: K
authors.lastname: Kangawa
authors.forename: Tadashi
authors.initials: T
authors.lastname: Tanabe
mesh_terms: D000208:Acute Disease; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000172:deficiency / Q000378:metabolism*; D006339:Heart Rate / Q000187:drug effects; D006973:Hypertension / Q000209:etiology; D007022:Hypotension / Q000139:chemically induced / Q000150:complications; D000860:Hypoxia / Q000150:complications / Q000503:physiopathology*; D019329:Idazoxan / Q000494:pharmacology; D019746:Intramolecular Oxidoreductases / Q000172:deficiency / Q000378:metabolism*; D008297:Male; D008469:Meclofenamic Acid / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009433:Neural Inhibition; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D012119:Respiration / Q000187:drug effects; D013564:Sympathetic Nervous System / Q000503:physiopathology*
chemical_list: D000317:Adrenergic alpha-Antagonists; D016861:Cyclooxygenase Inhibitors; D018341:Receptors, Adrenergic, alpha-2; D008469:Meclofenamic Acid; D003577:Cytochrome P-450 Enzyme System; D019746:Intramolecular Oxidoreductases; C022461:prostacyclin synthetase; D019329:Idazoxan