Lack of involvement of endothelin-1 in angiotensin II-induced contraction of the isolated rat tail artery

Effects of resistance training on arterial compliance and plasma endothelin-1 levels in healthy men

Arterial compliance (AC) is an index of the elasticity of large arteries. Endothelial dysfunction has been reported to result in reduced arterial compliance, which represents increased arterial stiffness. A reduction in AC is elicited by high-intensity resistance training, however the mechanisms are obscure. Because a single bout of resistance exercise causes a transient increase in circulating plasma endothelin-1 in humans, some vasoconstrictors may play a role in the mechanisms. The present study aimed to investigate whether resistance training-induced decrease in AC is associated with changes in circulating vasoconstrictors levels in young men. Young sedentary men were assigned to control (n=5) or training (n=9) groups. The training group performed four-week high-intensity resistance training (weight training exercise; three sessions/week). We measured AC and plasma levels of endothelin-1, angiotensin II, and norepinephrine before and after intervention. Resistance training significantly decreased AC, whereas the changes in plasma levels of neither endothelin-1, nor angiotensin II, nor norepinephrine were significantly different between the control and the training groups. Moreover, we found no significant correlations between changes in circulating plasma levels (endothelin-1, angiotensin II, and norepinephrine) and in the AC. Despite of no alteration of the resting circulating plasma levels (endothelin-1, etc.), we cannot exclude a possibility that the tissue/local concentrations of vasoconstrictors (endothelin-1, etc.) around the vessels might be increased and also involved in a reduction of AC in the training group. Taken together, the present results suggest that circulating vasoconstrictors (endothelin-1, etc.) in plasma are not involved in a reduction in AC by the resistance training.

Reduction of blood pressure by store-operated calcium channel blockers

The voltage-operated Ca(2+) channels (VOCC), which allow Ca(2+) influx from the extracellular space, are inhibited by anti-hypertensive agents such as verapamil and nifedipine. The Ca(2+) entering from outside into the cell triggers Ca(2+) release from the sarcoplasmic reticulum (SR) stores. To refill the depleted Ca(2+) stores in the SR, another type of Ca(2+) channels in the cell membrane, known as store-operated Ca(2+) channels (SOCC), are activated. These SOCCs are verapamil and nifedipine resistant, but are SKF 96465 (SK) and gadolinium (Gd(3+) ) sensitive. Both SK and Gd(3+) have been shown to reduce [Ca(2+) ]i in the smooth muscle, but their effects on blood pressure have not been reported. Our results demonstrated that both SK and Gd(3+) produced a dose-dependent reduction in blood pressure in rat. The combination of SK and verapamil produced an additive action in lowering the blood pressure. Furthermore, SK, but not Gd(3+) suppressed proliferation of vascular smooth muscle cells in the absence or presence of lysophosphatidic acid (LPA). SK decreased the elevation of [Ca(2+) ]i induced by LPA, endothelin-1 (ET-1) and angiotensin II (Ang II), but did not affect the norepinephrine (NE)-evoked increase in [Ca(2+) ]i . On the other hand, Gd(3+) inhibited the LPA and Ang II induced change in [Ca(2+) ]i , but had no effect on the ET-1 and NE induced increase in [Ca(2+) ]i . The combination of verapamil and SK abolished the LPA- or adenosine-5'-triphosphate (ATP)-induced [Ca(2+) ]i augmentation. These results suggest that SOCC inhibitors, like VOCC blocker, may serve as promising drugs for the treatment of hypertension.

Regulation of blood pressure and salt homeostasis by endothelin

Endothelin (ET) peptides and their receptors are intimately involved in the physiological control of systemic blood pressure and body Na homeostasis, exerting these effects through alterations in a host of circulating and local factors. Hormonal systems affected by ET include natriuretic peptides, aldosterone, catecholamines, and angiotensin. ET also directly regulates cardiac output, central and peripheral nervous system activity, renal Na and water excretion, systemic vascular resistance, and venous capacitance. ET regulation of these systems is often complex, sometimes involving opposing actions depending on which receptor isoform is activated, which cells are affected, and what other prevailing factors exist. A detailed understanding of this system is important; disordered regulation of the ET system is strongly associated with hypertension and dysregulated extracellular fluid volume homeostasis. In addition, ET receptor antagonists are being increasingly used for the treatment of a variety of diseases; while demonstrating benefit, these agents also have adverse effects on fluid retention that may substantially limit their clinical utility. This review provides a detailed analysis of how the ET system is involved in the control of blood pressure and Na homeostasis, focusing primarily on physiological regulation with some discussion of the role of the ET system in hypertension.

Endothelin-1-induced contraction is impaired in the tail artery of renal hypertensive rats

The contraction induced by endothelin-1 (ET-1) was evaluated in tail arteries from normotensive two-kidney (2K) and hypertensive two-kidney-one-clip (2K-1C) rats. Since the maximal effect induced by ET-1 (0.1-30 or 100 nmol/l) was lower in 2K-1C (1.11 +/- 0.10 g) than in 2K (1.46 +/- 0.14 g) tail arteries, we evaluated the possible mechanisms involved in this blunted response. The sensitivity and efficacy of ET-1 were not affected by endothelium removal in either group. ET-1 failed to induce contraction of 2K and 2K-1C arteries in Ca(2+)-free medium. The contractile response induced by 10 nmol/l ET-1 was similarly inhibited by 0.1 microM nifedipine in arteries from 2K (81.6 +/- 3.3%) and 2K-1C (81.3 +/- 3.8%) rats. The effect of nifedipine was not potentiated by 10 mumol/l SK&F 96365. The cytosolic Ca2+ concentration ([Ca2+]c) was similarly increased by 30 nmol/l ET-1 in smooth muscle cells isolated from tail arteries of 2K (30.80 +/- 11.94 nmol/l) and 2K-1C (54.06 +/- 10.98 nmol/l) rats. In conclusion, the blunted contraction induced by ET-1 in 2K-1C tail arteries was not dependent on the endothelium or on decreased Ca2+ influx through channels sensitive to nifedipine or SK&F 96365. Since the increase of [Ca2+]c upon stimulation with ET-1 was similar in 2K and 2K-1C tail artery cells, probably the sensitivity to Ca2+ is decreased in 2K-1C tail arteries.