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Inner medullary lactate production and accumulation: a vasa recta model
1Institut National de la Santé et de la Recherche Médicale Unité 467, Necker Faculty of Medicine, F-75015 Paris, France. srthomas@necker.fr
American Journal of Physiology. Renal Physiology
|September 1, 2000
Summary
Anaerobic glycolysis in the inner medulla produces lactate, a potential osmole that aids kidney concentrating ability. Numerical simulations show lactate recycling in vasa recta can create significant interstitial gradients.
Area of Science:
- Nephrology
- Physiology
- Computational Biology
Background:
- Inner medullary (IM) cell maintenance relies on ATP from anaerobic glycolysis.
- Lactate, a product of this process, is a potential source of
- external
- IM osmoles.
- Such osmoles could theoretically enhance the kidney's urine concentrating mechanism.
Purpose of the Study:
- To investigate if lactate produced by anaerobic glycolysis can accumulate in the IM interstitium.
- To estimate axial gradients of lactate and glucose via countercurrent recycling in IM vasa recta (IMVR).
Main Methods:
- Numerical simulation was used to model lactate and glucose transport.
- Assumed anaerobic glycolysis consumed 20% of delivered glucose, independent of diuretic state.
- Varied plausible values for lactate (P(LAC)) and glucose (P(GLU)) permeabilities in IMVR.
Main Results:
- High P(LAC) (100 x 10(-5) cm/s) facilitates efficient lactate recycling.
- Reduced P(GLU) (1/25th of P(LAC)) prevents papillary glucose depletion.
- Model predicts significant IM interstitial lactate gradients, potentially contributing 15 mM or more.
Conclusions:
- Metabolically produced lactate can accumulate as interstitial osmoles in the IM.
- This lactate accumulation can contribute to the kidney's concentrating ability, supporting the "single-effect" mechanism.
- The findings suggest a plausible source for interstitial osmoles previously hypothesized to improve renal concentrating capacity.