IngentaConnect HYPOTHALAMIC ANTIHYPERTENSIVE EFFECT OF METOPROLOL IN CHRONIC AOR...

Abstract:

SUMMARY

1. The aim of the present study was to investigate the possible hypothalamic antihypertensive effect of metoprolol and its action on aminergic neurotransmission in sham-operated (SO) rats and aortic coarctated (ACo) rats at a chronic hypertensive stage using the microdialysis technique.

2. Hypothalamic metoprolol concentrations and their cardiovascular effects were measured after the intravenous administration of 3 mg/kg metoprolol. Based on metoprolol concentrations reached in the anterior hypothalamus, in a second experiment the anterior hypothalamus of SO and ACo animals was perfused with Ringer's solution containing approximately 7.5 µg/mL metoprolol. The cardiovascular effects of metoprolol perfusion and changes in hypothalamic dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindol acetic acid (5-HIAA) levels were measured during the perfusion.

3. After i.v. administration of metoprolol, a greater hypotensive effect was observed in ACo rats than in SO animals ( Dgr

mean arterial pressure (MAP) -23.8 ± 2.1 vs-13.8 ± 1.3 mmHg, respectively; n = 5 for both groups). Metoprolol rapidly reached the central nervous system (CNS) in both groups of rats and its levels were similar in SO and ACo rats. Intrahypothalamic perfusion with metoprolol induced a significative decrease in blood pressure in ACo animals ( Dgr

MAP -13.3 ± 1.5 mmHg; n = 5; P < 0.05 vs Ringer perfusion), but not in SO rats ( Dgr

MAP 3.4 ± 2.7 mmHg; n = 5). Metoprolol perfusion reduced hypothalamic levels of DOPAC in ACo rats (65 ± 7% of basal levels; n = 5; P < 0.05 vs Ringer perfusion), but not in SO animals (87 ± 5% of basal levels; n = 5). There were no changes in hypothalamic concentrations 5-HIAA observed in either experimental group.

4. In conclusion, metoprolol exerts a greater hypotensive effect in chronic ACo animals, suggesting a participation of bgr

-adrenoceptors in the maintenance of the hypertensive stage. Metoprolol distribution in the CNS is not affected by ACo. The hypotensive effect of metoprolol perfusion in ACo rats suggested that hypothalamic bgr

-adrenoceptor blockade is part of the antihypertensive effect of metoprolol in chronic ACo rats. The effects of metoprolol on DOPAC levels suggest a reduction of dopamine turnover in hypertensive animals, but not in SO rats.

Keywords: anterior hypothalamus; aortic coarctation; central antihypertensive effect; metoprolol; microdialysis

Document Type: Original article

DOI: 10.1111/j.0305-1870.2005.04250.x

Affiliations: 1: Cátedra de Farmacología, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Buenos Aires, Argentina

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HYPOTHALAMIC ANTIHYPERTENSIVE EFFECT OF METOPROLOL IN CHRONIC AORTIC COARCTATED RATS