title: Mechanism behind augmentation in baroreflex sensitivity after acute exercise in spontaneously hypertensive rats.
abstract: A single bout of dynamic exercise increases baroreflex sensitivity (BRS) in spontaneously hypertensive rats (SHR). We examined whether change in hemodynamics (increases in blood pressure and heart rate) associated with dynamic exercise contribute to the post-exercise modulation of BRS. SHR aged 12 weeks were chronically instrumented with a carotid artery catheter and jugular vein catheter. They were then allocated to three groups submitted to 40 min of 1) running on a treadmill at 12 m/min (Run), 2) concomitant infusion of isoproterenol and a relatively high dose of phenylephrine (Iso+Phe(high)), or 3) concomitant infusion of isoproterenol and a relatively low dose of phenylephrine (Iso+Phe(low)). Arterial pressure and heart rate were continuously recorded throughout the experiments. BRS estimated by heart rate responses to phenylephrine injection and systolic blood pressure-low frequency power amplitude (SBP-LFamp) evaluated by power spectral analysis of SBP, a marker of sympathetic activity, were examined before and after running (Run group), or administration of drugs (Iso+Phe(high) or Iso+Phe(low) groups). BRS increased significantly from 1.4 to 1.9 bpm/mmHg after running, but not after administration of Iso+Phe(high) or Iso+Phe(low). Blood pressure and SBP-LFamp significantly decreased in each of the Run, Iso+Phe(high) and Iso+Phe(low) groups. These results suggest that hemodynamic change alone does not contribute to post-exercise modulation of BRS, while hemodynamic change or sympathetic activation during exercise contributes to post-exercise hypotension associated with a reduction of sympathetic activity.
authors.affiliation: Department of Internal Medicine and Rehabilitation Science, Tohoku University Graduate School of Medicine, 1-1 Seiryo-cho, Aoba-ku, Sendai 980-8574, Japan. minaoyo@mail.tains.tohoku.ac.jp
authors.forename: Naoyoshi
authors.initials: N
authors.lastname: Minami
authors.forename: Nobuyoshi
authors.initials: N
authors.lastname: Mori
authors.forename: Makoto
authors.initials: M
authors.lastname: Nagasaka
authors.forename: Osamu
authors.initials: O
authors.lastname: Ito
authors.forename: Hajime
authors.initials: H
authors.lastname: Kurosawa
authors.forename: Masayuki
authors.initials: M
authors.lastname: Kanazawa
authors.forename: Ki
authors.initials: K
authors.lastname: Kaku
authors.forename: Eigyoku
authors.initials: E
authors.lastname: Lee
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kohzuki
mesh_terms: D000818:Animals; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D002316:Cardiotonic Agents; D006339:Heart Rate; D006973:Hypertension / Q000503:physiopathology*; D007545:Isoproterenol; D008297:Male; D010656:Phenylephrine; D010805:Physical Conditioning, Animal / Q000502:physiology*; D051381:Rats; D011918:Rats, Inbred SHR
chemical_list: D002316:Cardiotonic Agents; D010656:Phenylephrine; D007545:Isoproterenol