刺激脑内渗透压感受器对大鼠浅表肾单位功能的影响

EFFECT OF BRAIN OSMORECEPTOR STIMULATION ON THE FUNCTION OF SUPERFICIAL NEPHRONS IN THE RAT

我们先前已在麻醉大鼠中用锂清除率方法从全肾水平证实,脑室内注射高张盐水(icv.HS)引起的利尿和利尿钠反应是由于肾小球滤过率增加和近球小管重吸收能力降低。本实验用肾小管微穿刺方法从肾单位水平进一步观察icv.HS对浅表肾单位的单个肾单位肾小球滤过率以及近曲小管和髓袢的重吸收的影响。实验在麻醉大鼠中进行。icv.HS后,单个肾单位肾小球滤过率从39.6±1.9nl/min增加至48.8±2.0nl/min(P<0.001);近曲小管末段小管液流量从20.5±1.4nl/min增加至28.4±2.0nl/min(P<0.001);小管液菊糖浓度与血浆菊糖浓度的比值从1.98±0.98降低至1.69±0.05(P<0.01)。根据上述数据计算得到的近曲小管重吸收分数从49.2±2.2％下降至41.7±1.8％(P<0.001),而近曲小管的绝对重吸收无明显改变。这些结果与用锂清除率方法获得的结果相符合。icv.HS后,髓袢的绝对重吸收升高,而重吸收分数下降。上述结果表明刺激脑内渗透压感受器可增加浅表肾单位的肾小球滤过率,并降低近曲小管的重吸收能力,从而增加髓袢的负荷,使髓袢的绝对重吸收增加。本实验结果不能排除icv.HS对髓袢的重吸收过程具有直接影响的可能性。

Our previous work with lithium clearance method indicated that the diuresisand natriuresis induced by intracerebroventricular administration of hypertonicsaline (icv. HS) resulted from an increase in glomerular filtration rate and a de-crease in water and sodium reabsorption in the proximal tubules. In the presentstudy, we further observed the effect of icv. HS on the glomerular filtration rateand proximal convoluted tubular and loop reabsorption in the superficial nephronswith micropuncture technique. After icv. HS, single nephron glomerular filtra-tion rate increased from 39.6±1.9 nl/min to 48.8±2.0 ml/min (P<0.001),late proximal convoluted tubular fluid flow rate increased from 20.5±1.4 nl/minto 28.4±2.0 nl/min (P<0.01), and the ratio of tubular fluid inulin concentrationto plasma inulin concentration decreased from 1.98±0.08 to 1.69±0.05 (P<0.01). Calculated fractional proximal convoluted tubular fluid reabsorptiondecreased from 49.2±2.2% to 41.7±1.8% (P<0.001), while calculated absoluteproximal convoluted tubular fluid reabsorption did not change significantly. Theseresults coincided with the observation with lithium clearance method. In addi-tion, icv. HS increased absolute loop fluid reabsorption but decreased fractionalloop fluid reabsorption. The present data suggest that stimulation of the brainosmoreceptor increases the glomerular filtration rate and decreases the reabsorptioncapacity of the proximal convoluted tubule in the superficial nephrons, both theseresponses result in an increase in the load of the loop of Henle with a secondarychange in loop reabsorption. However, the results of the present study do notrule out the possibility that icv. HS may also inhibit the loop reabsorption di-rectly.