Myogenic tone in mesenteric arteries from spontaneously hypertensive rats. Izzard, Ashley S, Stuart J Bund, and Anthony M Heagerty. Department of Medicine, Manchester Royal Infirmary, Oxford Road, Manchester, UK
APStracts 2:0264H, 1995.
In order to investigate myogenic tone during the developmental and established phases of hypertension, segments of distal (6th order) mesenteric arteries from spontaneously hypertensive rats (SHR) at 5 and 20 weeks were isolated and pressurised in vitro and compared with vessels from age matched Wistar- Kyoto (WKY) control animals. At 5 weeks, tone was significantly enhanced in the SHR. At 20 weeks tone was no longer significantly increased over a wide pressure range although arteries from the SHR were able to maintain diameter at all pressures studied whereas vessels from the WKY exhibited forced distension at 180 and 200mmHg. From the relative slope of the pressure- diameter relationship (myogenic index), no increase in peak myogenic responsiveness was observed in arteries from the SHR at either time point. Passive lumen diameters were significantly decreased in arteries from SHR at both time points. From the total and passive mid- wall circumference- tension relationships, total tension was observed at a reduced mid- wall circumference in the SHR but increased absolute levels of total tension were not observed. The normalized mid- wall circumference- tension relationships in the two strains revealed increased total tension due to active tension development at a reduced normalized circumference at 5 weeks in the SHR. At 20 weeks the normalized mid- wall circumference-tension relationships in the two strains were identical. These results demonstrate that myogenic tone in mesenteric arteries is enhanced during the development of hypertension but not when it is established, except at high intraluminal pressures. 

Received 10 February 1995; accepted in final form 22 June 1995.
APS Manuscript Number H127-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.