INCREASED Na CONCENTRATION IN CSF IS INVOLVED IN MAINTAINING ARTERIAL PRESSURE IN DEHYDRATED RATS.

为了分析脱水大鼠在[Na]脑脊液（DELTAMAP/DELTA[Na]csf）减少时平均动脉压（MAP）下降幅度更大的机制，我们用钠敏感微电极在侧脑室（LV）和MAP测量了高渗动脉脑脊液（ACSF） （-400 mOsm）输注（INF）到有和没有主动脉去神经（SAD）的大鼠的左室（LV）。两组[Na]csf在INF开始后-1min均显著升高，在INF结束时达到最大值，神经正常大鼠为16.4<正负>2.4 meq/kg H_2O， SAD大鼠为20.5<正负>1.3 meq/kg H_2O (n=10)，两组间δ [Na]csf在整个实验过程中无显著差异。另一方面，在INF开始后6.0 ~ 17.0 min， SAD大鼠的MAP明显高于神经支配大鼠（p<0.05）， INF结束时，SAD大鼠和神经支配大鼠的MAP分别升高19.0<正负>2.3 mmHg和7.7<正负>1.4 mmHg （p<0.01）。在整个实验过程中，两组MAP的变化均与DELTA[Na]csf高度相关，但SAD大鼠的斜率比神经正常大鼠（r=0.97, p<0.001）陡2倍（r=0.97, p<0.001），与脱水大鼠相同（r=0.96, p<0.001）。为验证低渗INF进入脱水大鼠左室时MAP降低的机制，在[Na]csf逐渐降低至脱水前水平时，测定脱水大鼠[Na]csf、MAP、CVP （mmHg）和心输出量（CO,ml/min 100g）。计算总血管导度（TVC, (ml/min 100g) /mmHg）为TVC=CO/ (MAP-CVP)。随着[Na]csf的降低，MAP和CO降低，TVC升高，呈高相关性（r^2=0.94 ~ 0.96, p<0.001）。脑脊液[Na]的增加通过引起全身血管收缩和防止脱水时CO的减少来维持动脉压。

To analyze the mechanism of the greater decrease in mean arterial pressure (MAP) at a given decrease in [Na]csf (DELTAMAP/DELTA[Na]csf) in dehydrated rats, we measured [Na]csf with a Na sensitive microelectrode in the lateral ventricle (LV) and MAP during infusion (INF) of hypertonic arterial cerebrospinal fluid (ACSF) (-400 mOsm) into the LV of rats with and without sino-aortic denervation (SAD). [Na]csf in both groups increased significantly -1min after the start of INF and attained the maximal increases of 16.4<plus-minus>2.4 meq/kg H_2O in innervated rats and 20.5<plus-minus>1.3 meq/kg H_2 in SAD rats (n=10) at the end of INF.There was no significant difference in DELTA[Na]csf between the two groups throughout the experiment. On the other hand, MAP in SAD rats increased to a significantly higher level than in innervated rats from 6.0 to 17.0 min after the start of INF (p<0.05) and the increase at the end of INF was 19.0<plus-minus>2.3 mmHg and 7.7<plus-minus>1.4 mmHg in the SAD and innervated rats, respectively (p<0.01). Changes in MAP in both groups were highly correlated with DELTA[Na]csf throughout the experiment, but the slope was steeper by two-folds in SAD rats (r=0.97, p<0.001) than that in innervated rats (r=0.97, p<0.001) and was identical to that in dehydrated rats (r=0.96, p<0.001).To cralifiy the mechanism of the decrease in MAP during hypotonic INF into the LV of dehydrated rats, [Na]csf, MAP,CVP (mmHg), and cardiac output (CO,ml/min 100g) were measured in dehydrated rats when [Na]csf was gradually reduced to the pre-dehydrated level. Total vascular conductance (TVC, (ml/min 100g) /mmHg) was calculated as TVC=CO/ (MAP-CVP). MAP and CO decreased and TVC increased as [Na]csf decreased with high correlations (r^2=0.94-0.96, p<0.001).The increase in [Na]csf is important to maintain arterial pressure by causing systemic vasoconstriction and preventing the decrease in CO during dehydration.