Daniels F H, Arendshorst W J
Department of Biomedical Engineering, Duke University, Durham 27706.
Am J Physiol. 1990 Sep;259(3 Pt 2):F529-34. doi: 10.1152/ajprenal.1990.259.3.F529.
The steady-state behavior of the tubuloglomerular feedback system has been studied in detail, but little is known about its dynamics. However, kinetic data can provide insight regarding the contribution of feedback to autoregulatory responses. Accordingly, experiments were conducted in anesthetized, euvolemic, spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats to characterize the time course of changes in proximal tubular stop-flow pressure after step changes in the rate of orthograde perfusion of Henle's loop. We studied the responses both to increase in perfusion rate, which produced preglomerular vasoconstriction, and decreases in perfusion rate, which produced preglomerular vasodilation. In both strains, the pattern of induced stop-flow pressure transients consisted of a pure delay followed by a monoexponential decay to a new steady state. In SHR rats, delay times were shorter than in WKY rats, but response time constants were not significantly different in the two strains. However, response time constants for dilation were longer than for constriction in both strains. The delay times and relatively large response time constants observed indicate that tubuloglomerular feedback cannot mediate rapid autoregulatory responses to fluctuations in renal perfusion pressure. The response time of tubuloglomerular feedback is probably limited by both the time lag associated with fluid transit through the loop of Henle and a relatively slow rate-limiting step in the signal transduction process at the macula densa.
肾小管球反馈系统的稳态行为已得到详细研究，但对其动力学了解甚少。然而，动力学数据可以为反馈对自动调节反应的贡献提供见解。因此，我们对麻醉、血容量正常的自发性高血压（SHR）大鼠和血压正常的Wistar-Kyoto（WKY）大鼠进行了实验，以描述在髓袢顺行灌注速率发生阶跃变化后近端肾小管停流压力变化的时间进程。我们研究了灌注速率增加（导致肾小球前血管收缩）和灌注速率降低（导致肾小球前血管舒张）时的反应。在这两种品系中，诱导的停流压力瞬变模式均包括一个纯延迟，随后是单指数衰减至新的稳态。在SHR大鼠中，延迟时间比WKY大鼠短，但两种品系的反应时间常数无显著差异。然而，在两种品系中，舒张的反应时间常数均长于收缩的反应时间常数。观察到的延迟时间和相对较大的反应时间常数表明，肾小管球反馈不能介导对肾灌注压波动的快速自动调节反应。肾小管球反馈的反应时间可能受与液体通过髓袢转运相关的时间滞后以及致密斑信号转导过程中相对较慢的限速步骤的限制。
