Effect of acute volume loading on aortic smooth muscle activity in intact dogs.

Experiments were performed to study the aortic smooth muscle responses to acute volume loading with dextran 70. To analyze the aortic smooth muscle activity, diastolic aortic pressure was plotted vs. aortic internal diameter to obtain a pressure-diameter relationship (PDR) curve. Aortic pressure and diameter were measured by means of a catheter-tip instrument. To obtain the relationships over a large range of pressure and diameter, slow oscillations (period, 4-5 s) in aortic pressure were induced by means of an external pump. In 15 anesthetized dogs, the blood volume was expanded by 33.6 +/- 0.6% (SE) of the control volume. After this volume expansion, aortic diameter for a given pressure was increased by 6.0 +/- 1.0% of the control value. The slope of the PDR curve for a given pressure was decreased by 16.1 +/- 3.9%, and the compliance per centimeter was increased by 30.2 +/- 5.9%. All these changes were significant at P less than 0.001. It was also shown that these responses were not related to the changes in mean arterial pressure and were not mediated by reflexes through the carotid sinus and vagus nerves.