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Title:Spontaneous rhythmic contractions in the coarcted aorta of hypertensive rats
Author(s):White, Charles Roger
Doctoral Committee Chair(s):Zehr, John E.
Department / Program:Molecular and Integrative Physiology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Biology, Animal Physiology
Abstract:We examined the contractile behavior of isolated, arterial ring segments excised from Sprague-Dawley rats which had undergone a complete occlusion of the aorta between the origin of the renal arteries. Eight days post-occulsion, measurements in awake rats showed that arterial pressure in the thoracic aorta (pressure-loaded region) was 168.35 $\pm$ 1.28 mm Hg (n = 104), while in the abdominal aorta (pressure-protected region) arterial pressure was 39.94 $\pm$ 2.40 mm Hg (n = 40). Aortic ring segments, removed from each region, were mounted in isolated muscle baths and loaded with 1.5 g initial tension for 90-120 minutes prior to the commencement of studies.
Since the hormonal environment of the pressure-loaded and pressure-protected regions must be the same, we propose that the rhythmic behavior seen in the pressure-loaded aorta is a result of the increased stretch imposed on this region of the vascular tree. Spontaneous rhythmic activity was dependent on the presence of extracellular calcium, since calcium depletion experiments and pharmacological blockade of voltage-sensitive calcium channels with dihydropyridine, ($-$) 202-791, abolished this contractile behavior in a dose-dependent manner. The administration of the dihydropyridine, calcium channel activator, (+) 202-791, enhanced rhythmic contractile activity in pressure-loaded ring segments and induced this contractile behavior in corresponding vascular regions in sham-operated rats. This finding suggests that rhythmic activity is produced when the intracellular concentration of calcium reaches a critical threshold level.
An increased Na$\sp+$ -K$\sp+$ pump activity is suggested by our finding that the time course of maximum tension development in response to bolus injection of ouabain (1.30 $\times$ 10$\sp{-3}$ M) was faster in pressure-loaded ring segments.
The blockade of voltage-sensitive potassium channels by tetraethylammonium chloride (TEA) promoted rhythmic contractile activity in pressure-loaded ring segments and induced this contractile behavior in thoracic ring segments taken from sham-operated rats. An increased sensitivity of pressure-loaded ring segments to TEA was revealed by a leftward shift in the ED$\sb{50}$ from the value observed in thoracic segments of sham-operated rats. On the other hand, apamin, a blocker of calcium-dependent potassium efflux, decreased the frequency of rhythmic contractions, suggesting a role for these membrane channels in the production of spontaneous rhythmic activity. (Abstract shortened with permission of author.)
Issue Date:1989
Rights Information:Copyright 1989 White, Charles Roger
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9011075
OCLC Identifier:(UMI)AAI9011075

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