Renal Transport of Lactate

Inherited Fanconi syndrome

BACKGROUND

Fanconi-Debré-de Toni syndrome (also known as Fanconi renotubular syndrome, or FRST) profoundly increased the understanding of the functions of the proximal convoluted tubule (PCT) and provided important insights into the pathophysiology of several kidney diseases and drug toxicities.

DATA SOURCES

We searched Pubmed and Scopus databases to find relevant articles about FRST. This review article focuses on the physiology of the PCT, as well as on the physiopathology of FRST in children, its diagnosis, and treatment.

RESULTS

FRST encompasses a wide variety of inherited and acquired PCT alterations that lead to impairment of PCT reabsorption. In children, FRST often presents as a secondary feature of systemic disorders that impair energy supply, such as Lowe's syndrome, Dent's disease, cystinosis, hereditary fructose intolerance, galactosemia, tyrosinemia, Alport syndrome, and Wilson's disease. Although rare, congenital causes of FRST greatly impact the morbidity and mortality of patients and impose diagnostic challenges. Furthermore, its treatment is diverse and considers the ability of the clinician to identify the correct etiology of the disease.

CONCLUSION

The early diagnosis and treatment of pediatric patients with FRST improve the prognosis and the quality of life.

Retrospective evaluation of the influence of azotemia on plasma lactate concentrations in hypotensive dogs and cats (2008-2018): 337 cases

OBJECTIVE

To evaluate the relationship between azotemia and plasma lactate concentration in hypotensive dogs and cats presented to an emergency department.

DESIGN

Retrospective case-control study.

SETTING

University veterinary teaching hospital.

ANIMALS

The electronic medical record database was searched for dogs and cats presented to the emergency department that had severe azotemia (creatinine ≥ 443.1 μmol/L [5 mg/dL]), hypotension (systolic blood pressure ≤ 90 mm Hg), and a plasma lactate measurement within 2 h of each another. Non-azotemic, normotensive dogs and cats; non-azotemic, hypotensive dogs and cats; and azotemic, normotensive dogs and cats that presented to the emergency department were used as control populations.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Severely azotemic, hypotensive dogs (n = 10) and cats (n = 63) had a lower plasma lactate than non-azotemic, hypotensive dogs and cats (P = 0.031 and P < 0.001, respectively). Median plasma lactate concentrations in hypotensive dogs (1.75 mmol/L) and cats (1.90 mmol/L) with severe azotemia were within reference intervals.

CONCLUSIONS

Hypotensive dogs and cats with severe azotemia have decreased plasma lactate concentrations as compared to hypotensive, non-azotemic dogs and cats. The median plasma lactate in azotemic, hypotensive dogs and cats was within reference intervals. This may be due to either decreased cellular production of lactate or increased excretion of lactate. Further research is needed to determine which of these mechanisms is responsible and the clinical significance of plasma lactate concentrations in azotemic, hypotensive dogs and cats.

Biochemical characterisation of para-aminophenol-induced nephrotoxic lesions in the F344 rat

The acute biochemical effects of the nephrotoxin p-aminophenol (PAP) were studied in detail using a combination of conventional bioanalytical and 1H-NMR spectroscopic methods. Dosing PAP (25-100 mg/kg) to male F344 rats resulted in a dose-related proximal nephropathy with consequent elevations in urinary enzymes, glucose, and urine total protein as shown by conventional methodology. 1H-NMR spectroscopy at 400 MHz of urine from PAP-treated rats also revealed a characteristic glycosuria, with concomitant amino aciduria. The increased excretion of these compounds indicates functional defects in the proximal tubule and reduced solute reabsorption efficiency. In addition, 1H-NMR urinalysis and conventional enzymatic analysis showed a dose-related lactic aciduria. Other changes detected by 1H-NMR included a dose-related reduction in the excretion of citrate (confirmed by a conventional biochemical method) and an increase in the excretion of acetate. The degree of abnormalities shown by 1H-NMR urinalysis agreed well with histopathological observations and conventional biochemical indices of nephrotoxicity. 1H-NMR urinalysis therefore serves to highlight changes in the excretion of low MW urine components not routinely studied by conventional biochemical analysis.

Substrate utilization in the isolated perfused cortical thick ascending limb of rabbit nephron

Isolated segments of cortical thick ascending limbs (cTAL) of rabbit kidney were perfused in vitro and the equivalent short circuit current (Isc) was measured. In a first series all substrates were removed on either side. Isc fell rapidly to 50 +/- 12% after 3 min and to 27 +/- 6% (n = 5) after 10 min. This indicates that in cTAL segments Isc is strictly dependent on the presence of substrates. In series two it was tested what substrates can be utilized by the cTAL segment, and from which epithelial side [bath (b) or lumen (1)] the substrates are taken up. From the 1-side only butyrate (10 mmol X 1(-1) sustained the Isc at 95 +/- 2% (n = 7). All other tested substrates (10 mmol X 1(-1): pyruvate, acetate, beta-OH-butyrate, D-glucose, and L-lactate lead to a marked decline in Isc. From the b-side several substrates (5--10 mmol X 1(-1) sustained the Isc: D-glucose, D-mannose, butyrate, beta-OH-butyrate, acetoacetate, L-lactate, acetate and pyruvate. Other compounds (1--10 mmol X 1(-1): citrate, alpha-ketoglutarate, succinate, glutamate, glutamine, propionate, caprylate and oleate did not sustain Isc. In the third series the mechanism of substrate utilization from the basolateral cell side was studied. It was shown that the Isc is a saturable function of the D-glucose, L-lactate, acetate, pyruvate or beta-OH-butyrate concentration with apparent Km's between 0.05--1.0 mmol X 1(-1). Several known inhibitors of sugar and of anion transport were tested at the bath side: phlorrhizin was without effect. Phloretin (500 mumol X 1(-1) inhibited Isc by 96%, yet its effect was not dependent on the presence of substrates on the b-side since inhibition occurred also if the b-perfusate contained no substrate and Isc was driven by luminal butyrate. Also SITS (5 mmol X 1(-1) exerted only a small inhibitory effect which was not specific since it was also observed with luminal butyrate. alpha-Cyano-m-OH-cinnamate (10 mmol X 1(-1) inhibited the Isc specifically when L-lactate was the bath substrate. Probenecid (1 mmol X 1(-1) had a similar yet less marked inhibitory effect. The D-glucose uptake from the b-side was specifically inhibited by cytochalasin B at 5 X 10(-6) mol X 1(-1). We conclude that the cTAL segment of the rabbit utilizes D-glucose and/or small anions such as pyruvate or L-lactate or acetate to energize salt reabsorption.(ABSTRACT TRUNCATED AT 400 WORDS)