The study for the myogenic response and intracellular calcium level in resistance arterioles from hypertensive or cardiac failure rats.

小动脉的肌源性反应可能参与调节总外周阻力，从而引起血管阻力。为了阐明生肌反应是否参与高血压的发生发展，我们用体外系统评价了高血压前期(4-5周龄)和高血压早期(7-8周龄)自发性高血压大鼠(SHR)提睾肌小动脉的生肌反应，并与年龄匹配的Wistar京都大鼠(WKY)进行比较。当血管内压升高15 mm Hg或30 mm Hg时，7~8周龄SHR(4~5周龄除外)的肌源性反应明显优于WKY。在用KCl引起电压依赖性钙通道(VDCC)收缩的敏感性评价中，KCl浓度-反应曲线的EC_(50)在7-8周龄显著降低，但在4-5周龄SHR与WKY相比无明显变化。]i当压力升高15 mm Hg时，SHR的升高幅度更大；当压力升高30 mm Hg时，SHR的升高更为显著。30 mm Hg尼群地平对自发性高血压大鼠的生肌反应的抑制作用更强。随着高血压的发展，自发性高血压大鼠VDCC的生肌反应和敏感性增强。因此，自发性高血压患者的肌源性反应增强，这可能是由于VDCC的敏感性增加所致。

The myogenic response of arterioles, which induce vascular resistance, may be involved in regulating the total peripheral resistance. To clarify whether myogenic response is involved in the development of hypertension, we evaluated the myogenic response of arterioles isolated from the cremaster muscle of spontaneously hypertensive rats (SHR) at a prehypertensive stage (4-5 weeks old) and at an early stage of hypertension (7-8 weeks old) as compared with age matched Wistar Kyoto rats (WKY) using an in vitro systems. The myogenic response of SHR aged 7-8 weeks (but not those aged 4-5 weeks) significantly exceeded that of WKY when intravascular pressure was increased by either 15 mmHg or 30 mmHg. In evaluating the sensitivity of the voltage dependent calcium channel (VDCC) by inducing contraciton with KCl, the EC_<50> of the concentration-response curve of KCl was significantly reduced in the 7-8 week-old, but not in the 4-5 week-old SHR vs. WKY.Measurement of intracellular levels of free calcium ([Ca^<2+>]i) in arterioles of the 7-8 week-old SHR and WKY loaded with a calcium-sensitive dye showed that, during the myogenic response, changes in [Ca^<2+>] i when the pessure was elevated by 15 mmHg tended to be greater in SHR ; the increase was significant when pressue was elevated by 30 mmHg. The inhibition of the myogenic response induced by nitrendipine at 30 mmHg was greater in SHR.The myogenic response and sensitivity of VDCC increased in SHR with the development of hypertension. Thus, the myogenic response was enhanced in SHR,and may be explained in part by an increase in sensitivity of the VDCC.