In situ aortic pressure-diameter relationship and structural changes in long-term chemical sympathectomized rats. Lacolley, Patrick, Emmanuel Glaser, Pascal Challande, Pierre Boutouyrie, Jean-Pierre Mignot, Micheline Duriez, Bernard Levy, Michel Safar, St[acute]ephane Laurent. Department of Pharmacology (P.B., S.L.), the "Institut National de la Sant[acute]e et de la Recherche M[acute]edicale" INSERM U337 (P.L., E.G., M.S.) and U141 (M.D., B.L.), Paris, and URA CNRS 879, Saint-Cyr l'Ecole (P.C.), France and ASULAB Research Laboratories, Neuchatel, Switzerland (JP.M.).
APStracts 2:0110H, 1995.
The purpose of the present study was to determine the effects of long -term chemical sympathectomy with guanethidine (GN) on the mechanical properties and the composition of the distal abdominal aorta in Wistar rats. GN was daily administered for 3 months (3M-GN, from 1 to 12 weeks), 5 weeks (5W-GN, from 7 to 12 weeks) and 8 days (8D-GN, from 11 to 12 weeks). All experiments were performed at 12 weeks of age to avoid age differences at examination. We used a high resolution echotracking system to determine in situ, in the systolic -diastolic range, the aortic diameter-, compliance-, and distensibility-pressure curves in anaesthetized rats. We observed an equivalent significant fall in the tyramine pressor response in all conscious GN-treated rats. Blood pressure was not affected by sympathectomy after 8 days and 5 weeks of treatment but was significantly reduced in 3 M-GN rats. Chronic sympathetic denervation increased aortic diameter and compliance in 8 D-GN rats, compared with those obtained at the same distending pressure in control rats, suggesting vascular smooth muscle relaxation. By contrast, in 5 W- and 3 M-GN rats, the distensibility pressure-curves were significantly shifted towards lower levels of distensibility and pressure, indicating a decreased aortic distensibility at the same level of arterial pressure. Sympathectomy produced a significant reduction in the content of elastin, one of the most distensible component of the arterial wall in 5 W- and 3 M-GN rats. These results suggest that intact sympathetic nerves are necessary to maintain normal functional and structural properties of large arteries in rat. The reduction in aortic distensibility, in long-term sympathectomized rats, could have resulted from complex interactions between local aortic denervation, change in the set point of distending pressure, and changes in aortic smooth muscle tone and/or wall composition. 

Received 19 September 1994; accepted in final form 1 March 1995.
APS Manuscript Number H839-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  4 April 1995.