Substrate uptake and utilization by the kidney of fed and starved rats in vivo.
Level 5 - mechanism / opinion, no new human data
Animal physiological study (in vivo rat model)
PubMed 7506440 · doi:10.1159/000173777
What was done
Renal blood flow, urinary flow, and renal substrate handling rates were evaluated in vivo in anesthetized fed versus 72-hour-starved rats. Concentrations of 12 metabolites were simultaneously measured in arterial whole blood, renal venous whole blood, plasma, and urine using enzymatic cycling microassays to evaluate total uptake and distinguish net luminal from peritubular transport.
What was found
The abstract reports directional shifts without reporting numerical values or statistical bounds. In fed rats, glucose and lactate were the primary potential energy sources, followed by fatty acids, ketone bodies, citrate, and glycerol. A 72-hour fast caused a large increase in renal uptake and metabolism of fatty acids, ketone bodies, glutamine, and glycerol, alongside large inhibition of lactate utilization. Net peritubular uptake of acetoacetate, citrate, glycerol, and free fatty acids occurred in both states, but starvation increased this uptake only for glycerol and free fatty acids. Starvation also stimulated net peritubular efflux of beta-hydroxybutyrate and ammonium ions, and converted glutamine handling into net peritubular uptake.
Why it matters
This study provides an in vivo baseline mapping how prolonged fasting reprograms renal fuel preference and alters basolateral versus luminal metabolite transport.
Limits
The study was conducted in an anesthetized rat model, limiting direct translation to human physiology. The abstract provides no animal sample sizes, exact quantitative rates, or statistical significance metrics.
Cited by
- contradicts The kidney nephron uses ketones as its primary fuel rather than glucose.