Differential effect of simulated microgravity on myogenic tone of middle cerebral and mesenteric small arteries in rats / 生理学报

The aim of the present study was to investigate the effect of a short-term (3-day) simulated microgravity with and without daily dorsoventral gravitation (-G(x)) for 1 h on myogenic tone and vasoconstrictor responsiveness of the middle cerebral artery and mesenteric third-order small artery in rats. The tail-suspension (SUS) model was used to simulate cardiovascular deconditioning due to microgravity. Daily restoring to normal standing (STD) posture for 1 h was adopted to provide -G(x) as the countermeasure. Segments of middle cerebral artery and mesenteric third-order small artery were isolated and cannulated. Vascular diameters in response to increased intraluminal pressure (from 20 mmHg to 120 mmHg, by 20 mmHg steps) of isolated arteries under no-flow conditions were recorded by a Pressure Myograph System in both physiologic salt solution (PSS) (active diameter, Da) and calcium-free PSS (passive diameter, Dp). The myogenic tone was calculated by (Dp-Da)/Dpx100%. Vasoconstrictor responsiveness of the isolated middle cerebral artery to serotonin and that of small mesenteric artery to phenylephrine were assessed in the PSS under an intraluminal pressure of 40 mmHg. The results showed that SUS induced an enhancement of the myogenic tone and vasoconstrictor responsiveness in the isolated middle cerebral artery but a depression of those in the small mesenteric artery. Daily STD for 1 h prevented the depression of myogenic tone and vasoconstrictor responsiveness in the small mesenteric artery, but did not prevent the functional enhancement in the middle cerebral artery. These data suggest that a short-term simulated microgravity may result in different alterations in the function of the cerebral artery and the resistance vessel in the hind-body. Moreover, only the decrease of function in these resistance vessels, not in the cerebral arteries, can be prevented by such a countermeasure of daily STD for 1 h.

Quantification of mRNA expression for angiotensinogen in rat arterial tissues by real-time PCR / 中国应用生理学杂志

<p><b>AIM</b>To develop a real-time PCR method for quantifying low abundance mRNA expression in rat arterial tissues and examine differential changes of angiotensinogen (AGT) gene expression in basilar and femoral arterial tissues after 8 weeks simulated weightlessness.</p><p><b>METHODS</b>After 8-wk of simulation, basilar and femoral arteries were harvested from both simulated weightless (SUS) and control (CON) rats. Then total RNA was extracted and reverse transcribed. The real-time PCR using TaqMan-MGB probe was performed to quantify AGT mRNA expression. The amplification efficiency (E) of PCR was calculated from the slope of standard curve. The threshold cycle (Ct) was detected by changes in fluorescence during a real-time PCR. Finally, the relative expression ratio of the target gene (AGT) to the reference gene (GAPDH) was calculated using E and Ct according to the mathematical model derived from the equation calculating the starting fluorescence (Ro).</p><p><b>RESULTS</b>After a 8-weeks simulated weightlessness, the AGT mRNA expression increased by 240 percent in basilar arterial, and decreased by 66 percent in femoral arterial tissues.</p><p><b>CONCLUSION</b>The specificity, sensitivity, precision, reproducibility, and simplicity of real-time PCR method using TaqMan-MGB probe make it particularly suitable for quantification of low abundance mRNA in arterial tissue from rats.</p>