The assessment of glomerular filtration rate in ponies and horses by sodium sulphanilate clearance

Use of a three-blood-sample plasma clearance technique to measure GFR in horses

Measurement of renal function in horses poses a particular challenge because plasma creatinine is influenced by muscle mass which is highly developed and variable between individuals, while conventional clearance methods involve potentially daunting problems, particularly urine collection and bladder washout. This paper provides data which enable technetium-diethyleneaminopentacetic acid (Tc-DTPA) clearance to be used to calculate glomerular filtration rate (GFR)/extracellular fluid volume (ECFV) as an expression of GFR in horses, as previously validated in humans, dogs and calves. Apart from being arguably a more physiological expression of GFR than using derivatives of body weight, the use of GFR/ECFV eliminates a source of delay and error, namely measurement of the injected dose, and offers the convenience of requiring only three blood samples. It therefore has advantages for both research and clinical applications.

Effects of inflammation-associated acute-phase response on hepatic and renal indices in the horse

OBJECTIVES

To determine the effect of an acute soft tissue inflammatory response on biochemical and haematological indices of hepatic and renal function in the Thoroughbred horse.

PROCEDURE

Soft tissue inflammation was induced in four Thoroughbred horses by intramuscular injections of Freund's complete adjuvant. The horses were clinically examined and blood and urine samples were collected before and after the adjuvant injections. Biochemical and haematological indices were measured in samples collected and used to determine the onset of the acute-phase response and to assess hepatic and renal function at this time.

RESULTS

After adjuvant injection, significant increases (P < 0.01) in total white (13.1 +/- 1.4 x 10(9)/L) and neutrophil (10.2 +/- 1.2 x 109/L) cell counts, rectal temperature (39.7 +/- 0.5 degrees C) and various plasma protein concentrations, including fibrinogen (6.6 +/- 1.2 g/L), haptoglobin (1.3 +/- 0.1 g/L) and total protein (88.1 +/- 2.7 g/L), indicated the induction of an acute-phase response. This corresponded with significant reductions (P < 0.01) in the plasma elimination half-lives (t1/2 beta) sodium bromosulphthalein (3.13 +/- 0.05 to 2.82 +/- 0.07 min) and sodium sulphanilate (38.29 +/- 4.04 to 19.60 +/- 5.68 min) and reductions in the plasma activities of aspartate aminotransferase, glutamate dehydrogenase, creatine kinase, alkaline phosphatase, gamma glutamyl transferase; the urinary creatinine clearance ratios of sodium, chloride and potassium; and the urinary gamma glutamyl transferase-to-creatinine clearance ratios. (All values mean +/- SD.)

CONCLUSIONS

The effects of the acute-phase response on indices of hepatic and renal function in the horse suggest that the disposition of pharmacological agents administered at this time may be altered and that indices of acute inflammation should be interpreted cautiously.

The effect of inflammation on the disposition of phenylbutazone in thoroughbred horses

The effect of inflammation on the disposition of phenylbutazone (PBZ) was investigated in Thoroughbred horses. An initial study (n = 5) in which PBZ (8.8 mg/kg) was injected intravenously twice, 5 weeks apart, suggested that the administration of PBZ would not affect the plasma kinetics of a subsequent dose. Two other groups of horses were given PBZ at either 8.8 mg/kg (n = 5) or 4.4 mg/kg (n = 4). Soft tissue inflammation was then induced by the injection of Freud's adjuvant and the administration of PBZ was repeated at a dose level equivalent to, but five weeks later than, the initial dose. Inflammation did not appear to affect the plasma kinetics or the urinary excretion of PBZ and its metabolites, oxyphenbutazone (OPBZ) or hydroxyphenylbutazone (OHPBZ) when PBZ was administered at 8.8 mg/kg. However, small but significant increases (P < 0.05) in total body clearance (CLB; 29.2 +/- 3.9 vs. 43.8 +/- 8.1 mL/ h.kg) and the volume of distribution, calculated by area (Vd(area); 0.18+/- 0.05 vs. 0.25 +/- 0.03 L/kg) or at steady-state (Vd(SS); 0.17 +/- 0.04 vs. 0.25 +/- 0.03 L/ kg), were obtained in horses after adjuvant injection, compared to controls, when PBZ was administered at 4.4 mg/kg which corresponded to relatively higher tissues concentrations and lower plasma concentrations (calculated) at the time of maximum peripheral PBZ concentration. Soft tissue inflammation also induced a significantly (P < 0.05) higher amount of OPBZ in the urine 18 h after PBZ administration but the total urinary excretion of analytes over 48 h was unchanged. These results have possible implications regarding the administration of PBZ to the horse close to race-day.