Effect of High Blood Pressure Stress on Vascular Adrenergic Responsiveness in the Spontaneously Hypertensive Rat

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Abstract
A model in which partial ligation of the left external iliac artery results in a decrease in mean arterial blood pressure to the ipsilateral femoral artery (70 mmHg; protected) while mean pressure increases in the contralateral femoral artery (125 mmHg; unprotected) was used to determine the effect of high blood pressure stress on vascular adrenergic responsiveness. Age-matched (5 week old) male Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) were used in the study. Partial ligation was performed at 6 weeks of age and vascular reactivity studies undertaken at 10 weeks of age when the SHR were considered hypertensive (indirect systolic blood pressure greater than 150 mmHg). Force-tension analysis of femoral arterial rings revealed that all tissues contracted maximally at 1.0 gram of preload force. This value was used in subsequent studies on adrenergic responsiveness. Isoproterenol-induced relaxation was significantly attenuated in rings of vascular smooth muscle from unprotected femoral arteries of the SHR, however, the response of rings from protected arteries of the SHR was similar to that of the protected and unprotected arteries of the WKY animal. Unprotected arteries of the SHR exhibited a greater response to norepinephrine stimulation when compared to protected arteries of the SHR as well as unprotected and protected arteries of the WKY animal. This study suggests that alterations in vascular alpha- and beta-adrenergic responsiveness in the SHR are most probably due to the increase in blood pressure.