The effect of oral sodium acetate administration on plasma acetate concentration and acid-base state in horses

Physicochemical Analysis of Mixed Venous and Arterial Blood Acid-Base State in Horses at Core Temperature during and after Moderate-Intensity Exercise

The present study determined the independent contributions of temperature, strong ion difference ([SID]), total weak acid concentration ([Atot]) and PCO2 to changes in arterial and mixed venous [H+] and total carbon dioxide concentration ([TCO2]) during 37 min of moderate intensity exercise (~50% of heart rate max) and the first 60 min of recovery. Six horses were fitted with indwelling carotid and pulmonary artery (PA) catheters, had PA temperature measured, and had blood samples withdrawn for immediate analysis of plasma ion and gas concentrations. The increase in core temperature during exercise (+4.5 °C; p < 0.001) significantly (p < 0.05) increased PO2, PCO2, and [H+], but without a significant effect on [TCO2] (p > 0.01). The physicochemical acid-base approach was used to determine contributions of independent variables (except temperature) to the changes in [H+] and [TCO2]. In both arterial and venous blood, there was no acidosis during exercise and recovery despite significant (p < 0.05) increases in [lactate] and in venous PCO2. In arterial blood plasma, a mild alkalosis with exercise was due to primarily to a decrease in PCO2 (p < 0.05) and an increase in [SID] (p < 0.1). In venous blood plasma, a near absence of change in [H+] was due to the acidifying effects of increased PCO2 (p < 0.01) being offset by the alkalizing effects of increased [SID] (p < 0.05). The effect of temperature on PO2 (p < 0.001) resulted in an increased arterio-venous PO2 difference (p < 0.001) that would facilitate O2 transfer to contracting muscle. The simultaneous changes in the PCO2 and the concentrations of the other independent acid-base variables (contributions from individual strong and weak ions as manifest in [SID] and [Atot]) show complex, multilevel control of acid-base states in horses performing even moderate intensity exercise. Correction of acid-base variables to core body temperature presents a markedly different physiological response to exercise than that provided by variables measured and presented at an instrument temperature of 37 °C.

Total Carbon Dioxide in Adult Standardbred and Thoroughbred Horses

The TCO2 (total carbon dioxide) test is performed on the blood of racehorses as a means of combatting the practice of administering alkalizing agents for the purpose of enhancing performance. The purposes of this review are to present an overview of the factors contributing to TCO2 and to review the literature regarding TCO2 in adult Standardbred and Thoroughbred horses to demonstrate the range of variability of TCO2 in horses. Most of the research published on the topic of TCO2 or bicarbonate measurement in racehorses was accessed and reviewed. PubMed and Google Scholar were the primary search engines used to source the relevant literature. The main physicochemical factors that contribute to changes in TCO2 in horses at rest are changes in strong ions concentration, followed by changes in weak acid (i.e. plasma albumin) concentrations. There is a wide normal distribution of TCO2 in horses ranging from 23 mmol/L to 38 mmol/L. Independent of administration of alkalizing agents, blood TCO2 is affected mainly by feeding, time of day (diurnal variation), season and exercise. There are few studies that have reported hour-by-hour changes in TCO2. Racehorse population studies suffer from lack of validation regarding whether or not a horse was administered an alkalizing agent. It is concluded that the normal range of TCO2 in non-alkalized Standardbred and Thoroughbred horses is significantly wider than has been appreciated, that periods of elevated TCO2 appear to be normal for many horses at rest, and that a TCO2 test alone is not definitive for the purposes of determining of an alkalizing agent has been administered to a horse.

Alkalinizing effects of oral sodium bicarbonate and sodium acetate in sedentary horses

Equimolar solutions of sodium bicarbonate (NaHCO3) or sodium acetate (NaC2H3O2), or deionised water (as a negative control) were administered by nasogastric intubation randomly to each of 12 sedentary mares every 2 weeks. Anaerobic samples of jugular venous blood were obtained hourly until 7 h after administration and were analysed for pH, pCO2, and concentrations of tCO2, HCO3−, Na+, K+, Cl−, and Ca++. Measured strong ion difference (SIDm), anion gap (AG), and estimated strong ion gap (SIGest) were calculated. Least square means differences for each variable were determined using ANOVA for repeated measures. Significance level was set at P<0.05. Treatment with NaHCO3increased pH, pCO2, [tCO2], [HCO3−], [Na+], and SIDm within 1 h of intubation (P<0.05). Peaks were reached at 2 (pH and [Na+]) and 3 h (pH, pCO2, [tCO2], [HCO3−], and SIDm) after NaHCO3 treatment. Sodium acetate increased [Na+] within 1 h of intubation; pH, [tCO2], and [HCO3−] within 2 h; and pCO2 and SIDm within 3 h (P<0.05). Peaks in pCO2, [tCO2], and [HCO3−] (4 h) and in pH and SIDm (5 h) were later with NaC2H3O2 when compared with NaHCO3. Changes in AG, SIDm, and SIGest were delayed after NaC2H3O2 treatment, corresponding to the lags in venous pH, pCO2, [tCO2], and [HCO3−]. Serum [K+] decreased from 3 through 6 h for both treatments when compared to H2O control (P<0.05). Serum [Cl−] was decreased only for NaHCO3 at 3 h (P<0.05). Serum [Ca++] was decreased for NaHCO3 at 2, 3, 4, and 7 h and for NaC2H3O2 only at 3 h (P<0.05). It was concluded that oral NaC2H3O2in horses caused a metabolic alkalosis similar to that caused by oral NaHCO3, but that the peaks in pH, pCO2, [tCO2], [HCO3−], SIDm, AG, and SIGest were delayed after NaC2H3O2 treatment.

Oral acetate supplementation after prolonged moderate intensity exercise enhances early muscle glycogen resynthesis in horses

Oral acetate supplementation enhances glycogen synthesis in some mammals. However, while acetate is a significant energy source for skeletal muscle at rest in horses, its effects on glycogen resynthesis are unknown. We hypothesized that administration of an oral sodium acetate-acetic acid solution with a typical grain and hay meal after glycogen-depleting exercise would result in a rapid appearance of acetate in blood with rapid uptake by skeletal muscle. It was further hypothesized that acetate taken up by muscle would be converted to acetyl CoA (and acetylcarnitine), which would be metabolized to CO2 and water via the tricarboxylic acid cycle, generating ATP within the mitochondria and thereby allowing glucose taken up by muscle to be preferentially incorporated into glycogen. Gluteus medius biopsies and jugular venous blood were sampled from nine exercise-conditioned horses on two separate occasions, at rest and for 24 h following a competition exercise test (CET) designed to simulate the speed and endurance test of a 3 day event. After the CETs, horses were allowed water ad libitum and either 8 l of a hypertonic sodium acetate-acetic acid solution via nasogastric gavage followed by a typical hay-grain meal (acetate treatment) or a hay-grain meal alone (control treatment). The CET significantly decreased muscle glycogen concentration by 21 and 17% in the acetate and control treatments, respectively. Acetate supplementation resulted in a rapid and sustained increase in plasma [acetate]. Skeletal muscle [acetyl CoA] and [acetylcarnitine] were increased at 4 h of recovery in the acetate treatment, suggesting substantial tissue extraction of the supplemented acetate. Acetate supplementation also resulted in an enhanced rate of muscle glycogen resynthesis during the initial 4 h of the recovery period compared with the control treatment; however, by 24 h of recovery there was no difference in glycogen replenishment between trials. It is concluded that oral acetate could be an alternative energy source in the horse.