Shoko Osugi

Blood pressure and impairment of endothelium-dependent relaxation in spontaneously hypertensive rats

Correlation between hypertension and impairment of endothelium-dependent relaxation was demonstrated using aortae from certain strains of rats with various levels of spontaneous hypertension. It was also observed that the impairment of endothelium-dependent relaxation is the secondary change due to hypertension, and the level and duration of hypertension is the determinant factor of the impairment.

Effects of chronic treatment with SQ29852 on spontaneous smooth muscle tone and endothelium-dependent relaxation in aorta of stroke-prone spontaneously hypertensive rats.

The effects of chronic treatment with SQ29852, an angiotensin-converting enzyme inhibitor, on spontaneous smooth muscle tone and endothelium-dependent relaxation of aorta from stroke-prone spontaneously hypertensive rats (SHRSP) were studied and compared with those of captopril. Endothelium-removed aorta from 16-week-old SHRSP exhibited a high amplitude of spontaneously developed active tension (active tone), whereas no active tone was observed in the preparation from control normotensive Wistar-Kyoto (WKY) rats. Treatment with SQ29852 or captopril at age 5–16 weeks prevented the development of hypertension. No active tone could be detected in the preparation from SQ29852-treated SHRSP. Endothelium-dependent relaxation was markedly reduced in the preparation from non-treated SHRSP compared with WKY rats. Treatment with SQ29852 prevented the impairment of endothelium-dependent relaxation. It was also shown that norepinephrine-induced contraction was markedly depressed in en-dothelium-intact aorta from SQ29852-treated rats. The effects of SQ29852 were more prominent than those of hydralazine when blood pressure was maintained at similar levels. It was suggested that SQ29852 exerts an action on both vascular smooth muscle and endothelium that is mediated by the inhibition of angiotension-converting enzyme in addition to indirect actions of SQ29852 that are brought about by blood pressure lowering.

Impairment and protection of endothelium-dependent relaxation in aortae of various strains of spontaneously hypertensive rats

Endothelium-dependent relaxations of aortae from various strains of spontaneously hypertensive rats (SHR) were studied using SHR, stroke-prone SHR (SHRSP), and malignat SHRSP (M-SHRSP) of the Okamoto strain. Blood pressure of the rats was higher in the order of M-SHRSP>SHRSP>SHR. the endothelium-dependent relaxation of the aorta was impaired in these hypertensive rats compared with Wistar-Kyoto (WKY) rats. The impairment was age dependent and, when compared at the same age, greater in the following order: M-SHRSP>SHRSP>SHR.

Caffeine-induced contraction in arteries from stroke-prone spontaneously hypertensive rats

Differences in caffeine-induced contraction in smooth muscle of resistance vessels from stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar Kyoto rats (WKY) were investigated by using mesenteric artery preparations. The contraction induced by caffeine (10 mM) was greater in SHRSP preparations, both in the presence and absence of Ca (10 min after Ca removal). Caffeine-induced contraction was gradually decreased by the removal of extracellular Ca. No significant difference was observed in the time course of the decay of the contraction between SHRSP and WKY preparations, and the contraction disappeared when the time in Ca-free solution exceeded 80 min. The contraction induced by high-K-Tyrodes solution was completely abolished within 10 min after Ca removal, both in SHRSP and WKY preparations. Caffeine-induced contraction could be blocked by procaine or ryanodine. The results suggest that caffeine induces contraction by releasing Ca from sarcoplasmic reticulum, and that the release of Ca is greater in SHRSP vascular smooth muscle. It is also suggested that sarcoplasmic reticulum is leaky for stored Ca when extracellular Ca is removed, and that the rate of leakage does not differ between smooth muscle cells of SHRSP and WKY mesenteric arteries.

Influence of the Endothelium on the Elevation of Basal Tension in Aortae from Various Strains of Spontaneously Hypertensive Rats

The active tone of aortic smooth muscle of spontaneously hypertensive rats and its modulation by endothelium were studied using spontaneously hypertensive rats (SHR), stroke-prone SHR (SHRSP), and malignant SHRSP (M-SHRSP) of Okamoto strain. Wistar-Kyoto (WKY) rats were also used as control normotensive rats. Blood pressure (BP) of the animals was higher in the following order: WKY<SHR<SHRSP<M-SHRSP. The active tone was obtained by removing extracellular calcium (Ca) in the absence of a stimulant (normal Tyrodes solution).