Mechanical and biochemical alterations of aorta induced by hydralazine hypotension.

Previous experiments from this laboratory indicated that the actomyosin content of aorta from spontaneously hypertensive (SHR) rats was greater than that from normotensive (WKY) rats. The purpose of the present experiments was to determine the effect of hydralazine-induced hypotension on actomyosin content and mechanical properties of aorta from SHR and WKY rats. Ten-week-old WKY and SHR rats were given to tap water or tap water containing 80 mg/l of hydralazine for 2 weeks and at the end of this time the actomyosin content (sodium dodecyl sulfate-polyacrylamide gel electrophoresis), the contractile responses to potassium chloride and phenylephrine and the passive stress-strain properties of the aorta were determined. Hydralazine-treated rats had a significantly lower systolic pressure after 1 week which remained lower for the remainder of the treatment period. Treated WKY and SHR rats exhibited a reduced actomyosin content relative to total protein content of cell number (based on DNA determination). Mechanically, aorta from treated animals showed no change in their passive elastic properties or in their sensitivity (ED50) to either agonist; however, the maximum contractile response to both agonists was significantly reduced. Normalization of force development to actomyosin content indicated: 1) that aorta from SHR rats develop less force for a given amount of actomyosin than WKY aorta; 2) a 2-week period of hydralazine hypotension results in a reduction in force development in both WKY and SHR aorta that can be accounted for by a reduction in cellular actomyosin content; and 3) this period of hydralazine hypotension does not return the contractile effectiveness of actomyosin from SHR aorta to that of actomyosin from WKY aorta.