Homeostatic efficiency of tubuloglomerular feedback in hydropenia, euvolemia, and acute volume expansion.
We assessed the homeostatic efficiency of the tubuloglomerular feedback (TGF) system in Inactin-anesthetized Munich-Wistar rats by use of perturbation analysis in closed-loop micropuncture studies. Nephrons were studied in vivo under conditions of hydropenia (HYD, n = 17), euvolemia (EUV, n = 23), and acute isoncotic extracellular volume expansion (EXP, n = 15). Proximal tubular flow was perturbed in free-flowing nephrons with a microperfusion apparatus. Flow rate (VM) was measured upstream from the perturbation (VH) by a noninvasive optical technique. The dependence of VM on VH was estimated by polynomial regression. By using fractional compensation (C = -dVM/dVH), as an index of homeostatic efficiency, we constructed efficiency profiles (C vs. VH). At VH = 0, C tended toward higher values with decreasing volume status, although the effect did not achieve significance. The maximum value of C did not differ between groups. The efficiency profiles shifted leftward with each increment in volume (P < 0.03, HYD vs. EXP), suggesting that the TGF system adapts to acute increments in volume by shifting the efficiency profile in favor of a vasodilatory role.
Thomson
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SC
Department of Medicine, University of California, San Diego.
Blantz
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RC
D000818:Animals; D001810:Blood Volume; D005246:Feedback; D006706:Homeostasis; D007678:Kidney Glomerulus / Q000502:physiology*; D007684:Kidney Tubules / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D010952:Plasma Substitutes / Q000494:pharmacology*; D011677:Punctures; D051381:Rats; D011919:Rats, Inbred Strains; D014868:Water Deprivation / Q000502:physiology*
D010952:Plasma Substitutes