Modulation of chronotropic and inotropic heart vagus actions as a non-pressor effect of angiotensin II in the anaesthetized rat.
(1) In vagotomized, anaesthetized rats, effects of stimulation of cardiac N. vagus (2-25 Hz) on cardiac and circulatory functions were studied: we recorded transient reductions in heart rate (HR), in left-ventricular systolic pressure (LV Ps), in maximal change in left-ventricular pressure development (dp/dt)max and in mean arterial pressure (MAP, A. femoralis). (2) Bolus injection of angiotensin II (AII, 2.5-100 microg/kg body weight) caused (a) transient increases in HR, LV Ps and MAP (pressor effects, maximal changes occurred within 3 min after injection), and (b) dose-dependently reduced effects of vagus stimulation (non-pressor effects, recorded 10 min after injection). Due to fast breakdown of All in the circulatory system, all observed vagus stimulation effects were completely recovered within 1 h after injection. (3) Plasma concentration of AII was recorded with a highly specific radioimmunoassay: 10 min after AII injection (non-pressor range), plasma concentration was clearly higher than physiological levels in all experiments with 10 microg AII/kg at least. (4) Treatment with propranolol (beta-adrenoceptor blocker, 1 mg/kg body weight) did not reduce the vagus effects alone, but decreased the modulatory AII effects. This result hints at the activation of sympathetic beta-adrenergic receptors by AII counteracting the parasympathetic cardiac control.
Institute of Physiology II (Heart-Circulation Physiology), Medical Faculty, Friedrich Schiller University Jena, Germany.
C
C
Wicher
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Biewald
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M
Hüller
D000758:Anesthesia; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D003864:Depression, Chemical; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects*; D008297:Male; D009206:Myocardium; D051381:Rats; D014630:Vagus Nerve / Q000187:drug effects* / Q000502:physiology; D014662:Vasoconstrictor Agents / Q000494:pharmacology*
D014662:Vasoconstrictor Agents; D000804:Angiotensin II