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Angiotensin converting enzyme inhibition improves cardiac neuronal uptake of noradrenaline in spontaneously hypertensive rats

Raasch, Walter; Betge, Stefan; Dendorfer, Andreas; Bartels, Torsten; Dominiak, Peter

Original papers: Renin-angiotensin system

Objectives  It has been shown that a diminished sympathetic activity contributes to the hypotensive and cardioprotective actions of angiotensin converting enzyme (ACE) inhibitors (ACEI). Besides an inhibition of central sympathetic tone and peripheral noradrenaline release, we hypothesized that the interactions of ACEI with the sympathetic system may include a modulation of neuronal catecholamine uptake by peripheral nerves.

Design  We investigated the influence of fosinopril on noradrenergic uptake into cardiac neurones in vitro and in vivo in acute and chronic models.

Methods and results  Acute administration of fosinoprilat to isolated perfused rat hearts increased the extraction of [3H]-noradrenaline from the perfusate by 39%. Treatment (14 days) of spontaneously hypertensive rats (SHR) with fosinopril (20 mg/kg per day) enhanced the cardiac uptake of i.v. administered [3H]-noradrenaline by 28%. The endogenous left ventricular content of noradrenaline was increased by 49% after an antihypertensive treatment of SHR with fosinopril (20 mg/kg per day). Identical increases in cardiac noradrenaline stores (53%) were observed in SHR treated with a blood pressure ineffective dose of fosinopril (0.2 mg/kg per day). The myocardial content of adrenaline was increased in parallel to noradrenaline after both dose regimes.

Conclusions  It is concluded that ACEI increases neuronal uptake of catecholamines in SHR in a blood pressure-independent manner. This effect occurs acutely and is independent of central sympathetic activity. Therefore, we hypothesize that ACEI modulate the activity of the cardiac noradrenaline transporter by direct activation. The improved uptake of noradrenaline may contribute to the antihypertensive and cardioprotective effects of ACEI.

Institute of Experimental and Clinical Pharmacology and Toxicology, Medical University of Luebeck, Germany.

Correspondence and requests for reprints to Walter Raasch, Institute of Experimental and Clinical Pharmacology and Toxicology, Medical University of Luebeck, Ratzeburger Allee 160, 23538 Luebeck, Germany. Tel: +49 451 5002698; fax: +49 451 5003327; e-mail: raasch@medinf.mu-luebeck.de

Received 8 October 2000

Revised 23 April 2001

Accepted 7 May 2001

© 2001 Lippincott Williams & Wilkins, Inc.