Contractile Responses of Aortic and Portal Vein Strips during the Development of DOCA/Salt Hypertension

Abstract

Vascular smooth muscle strips were examined during the development of hypertension in rats treate.d with deoxycorticosterone acetate (DOCA) plus saline to determine if the changes in the contractile responses precede or succeed the increase in blood pressure. After treatment with DOCA/salt for 1,3 and 4 weeks, aortic and portal vein strips were prepared from control and treated rats for studies of cumulative dose-response relationships to noradrenaline (NA) in Krebs’ solutions containing normal (2.5 mM) or low (0.2 and 0.4 mM) concentrations of Ca. 1 week of treatment did not result in any change in blood pressure or in the stress (force/area) developed by the aortic strips in response to NA in normal or low Ca. 3 weeks of treatment caused a significant increase of pressure and the aortic strips developed a significant decrease of stress in response to NA in normal, but not in low Ca. 4 weeks of treatment resulted in a significant increase of pressure and a significant decrease of stress in response to NA in low, as well as in normal, Ca. In contrast to the aortic strips, there was no change in the force induced by NA in the portal vein strips at any time. Thus, the decrease of contractile response in the aortic strips during treatment with DOCA/salt followed the same time course as the increase of arterial pressure and may be a consequence of high blood pressure.

Effects of Hypertension on Morphological, Contractile and Mechanical Properties of Rat Aortic Smooth Muscle Cells

“…Han and Ku 10 cultured porcine common carotid artery segments under normotensive and hypertensive pressure conditions for 7 days and discovered that artery segments exposed to hypertensive conditions showed a stronger contractile response than segments exposed to normotensive conditions. In contrast, all of the studies that used aortic segments, 8,11,23,25 including the present study, have shown decreased contractility. The reason for this difference is unclear at this stage, but the difference could arise from the difference in specimen size.…”

“…A reduction of contractility in hypertensive subjects was also observed in previous studies with aortic segments. 8,11,23,25 The smooth muscle hypertrophy caused by the hypertension may be accompanied by an increase in biosynthetic activities with the increase in organelles associated with protein synthesis such as rough endoplasmic reticulum (RER) and Golgi apparatus, as occurring during the phenotypic transformation from a contractile to synthetic state. In return, the contractile response may be inhibited through the decrease in actin filaments.…”

“…1,13 With regard to contractile properties, reported results have been inconclusive: some have reported an increase in contractile properties, 4,6,19,29 while others have documented a decrease. 8,11,23,25 Contractile properties may depend on the artery types and experimental methods.…”