Relationship Between Aortic Reactivity and Blood Pressure of Renal Hypertensive, Hyperthyroid, and Hypothyroid Rats

Abstract

The reactivity of aortic rings from normotensive rats and from young rats with hypertension induced by bilateral renal encapsulation was compared. Aortae of hypertensive rats (190–250 mm Hg) produced greater isometric tension in the presence of norepinephrine (0.1 × to 3 × 10−9 M), serotonin (0.03 × to 1 × 10−6 M), and KCl (2.5 × to 10 mM) than did those of normotensive rats. A relationship exists between systolic blood pressure and aortic responsiveness to norepinephrine and KCl. Aortae from rats with borderline hypertension (140–150 mm Hg) exhibited supersensitivity only to low doses of KCl (2.5 and 5 mM), although those from rats with moderate hypertension (160–170 mm Hg) exhibited increased responsiveness to low doses of both norepinephrine (0.1, 0.3, and 1 × 10−9 M) and KCl (2.5, 5, and 10 mM), and these responses tended to be less than those produced by aortae from rats with severe hypertension (190–250 mm Hg). Hyperthyroid and hypothyroid rats had significantly higher and lower systolic blood pressures, respectively, than euthyroid rats. Aortae from hyperthyroid and hypothyroid rats were supersensitive and subsensitive, respectively, to low doses of norepinephrine and KCl. The rate of relaxation of aortic segments, after 80 mM KCl was washed from the bath with normal Krebs solution, was studied; hyperthyroid and hypothyroid rats yielded segments whose rates of relaxation were slower and faster, respectively, than those of euthyroid rats. Similarly, the rate of relaxation of aortic smooth muscle from renal hypertensive rats was inversely related to aortic reactivity to low doses of KCl. The relationship between vascular reactivity, blood pressure, and thyroid state is discussed. The aorta of renal encapsulated rats appears to be a useful model for studying smooth muscle supersensitivity and changes of vascular sensitivity associated with hypertension.