Determination of tonicity effects of ketoacids and lactate by use of two canine red blood cell assays.

OBJECTIVE

To determine the tonicity effects of β-hydroxybutyrate, acetoacetate, and lactate in canine RBCs.

SAMPLE

RBCs from approximately 40 dogs.

PROCEDURES

2 in vitro methods were used to conduct 4 experiments. The modified osmotic fragility assay was used to measure the ability of ketoacid salts added to serial sucrose dilutions to protect RBCs from osmotic hemolysis. In a second assay, a handheld cell counting device was used to measure changes in RBC diameter to assess the tonicity effect of solutions of ketoacid and lactate salts.

RESULTS

For the modified osmotic fragility assay, all ketoacid salts had an osmoprotective effect, but the effect was determined to be completely attributable to the tonicity effect of added cations (sodium and lithium) and not the ketoacid moieties. However, both the sodium and lithium lactate salts provided osmoprotection attributable to both the cation and lactate anion. For the second assay, RBC diameter was significantly increased with the addition of urea (an ineffective osmole) but did not change with the addition of glucose (an effective osmole), which established the behaviors of ineffective and effective osmoles in this assay. The RBC diameter was significantly increased over that of control samples by the addition of sodium β-hydroxybutyrate, lithium acetoacetate, and lithium lactate but was decreased by the addition of sodium lactate.

CONCLUSIONS AND CLINICAL RELEVANCE

For both assays, β-hydroxybutyrate and acetoacetate acted as ineffective osmoles, whereas lactate acted as an effective osmole in 3 of 4 experiments.