AJP - Renal Physiology, Vol 259, Issue 3 529-F534, Copyright © 1990 by American Physiological Society
Tubuloglomerular feedback kinetics in spontaneously hypertensive and Wistar-Kyoto rats
F. H. Daniels and W. J. Arendshorst
Department of Biomedical Engineering, Duke University, Durham 27706.
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.
