The elasticity of the thoracic aorta was studied in nine dogs instrumented with a pressure microtransducer and two ultrasonic crystals diametrically fixed in the adventitia. Systolic and diastolic changes in pressure and diameter were used to calculate Peterson and incremental elastic moduli. Acute hypertension was induced by infusions of angiotensin performed 1) during the control period, 2) after propranolol (1.5 mg/kg), 3) after atropine (0.2 mg/kg), and 4) after propranolol plus atropine.

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... solute and percent variations of mean diameter were correlated to pressure in the control period and after autonomic blockade (p<0.01). The slopes of these correlations were not different between propranolol and control groups, but were lower with atropine (p<0.01) and with atropine plus propranolol (p < 0.001) than in the control period. Correlations were also found between Peterson and incremental elastic moduli and mean pressure in the control period and after blockade (p < 0.001). No differences of slopes existed between propranolol and control groups, but the slope of the correlation relative to the incremental elastic modulus was higher with atropine than in the control period ( p < 0.05), and the slopes of the correlations relative to the Peterson and the incremental elastic moduli were respectively higher with atropine plus propranolol than in the control period (p<0.05, p<0.05). Thus, atropine decreased the distent ion and increased the stiffness of the aorta in response to acute angiotensin-mediated hypertension. (Hypertension 11 [Suppl I]: I-103-M07, 1988) KEY WORDS • parasympathetic and sympathetic nervous systems • aortic diameter • elastic modulus • atropine • propranolol • angiotensin From the Favaloro Foundation, Buenos Aires, Argentina (E.