Microdialysis measurements of equine lamellar perfusion and energy metabolism in response to physical and pharmacological manipulations of blood flow.
BACKGROUND
A suitable method for evaluating lamellar perfusion changes and their metabolic consequences is currently lacking.


OBJECTIVE
To examine perfusion changes in lamellar tissue using serial microdialysis measurements of urea clearance and energy metabolites.


METHODS
Randomised, controlled (within subject) experimental trial.


METHODS
Nine Standardbred horses were instrumented with microdialysis probes in the foot lamellar tissue and skin (over the tail base). Urea (20 mmol/l) was added to the perfusate and its clearance was used to estimate local perfusion. Samples were collected every 15 min for a 1 h control period, then during application of a distal limb tourniquet, during periods when norepinephrine or potassium chloride (KCl) were included in both skin and lamellar perfusates, and after systemic (intravenous) acetylpromazine. Dialysate concentrations of glucose, lactate, pyruvate and urea were measured and lactate:glucose (L:G) and lactate:pyruvate (L:P) ratios calculated. Values were compared with pre-intervention baseline and also between simultaneous skin and lamellar samples using nonparametric statistical methods.


RESULTS
Lamellar glucose decreased and lactate, urea, L:G and L:P increased significantly with tourniquet application, without significant changes in skin dialysate values. Lamellar and skin glucose decreased and L:G increased significantly during norepinephrine infusion, but mild increases in urea were not significant at either site. KCl caused significant decreases in lamellar and skin L:G, and an increase in skin glucose, but did not affect urea clearance. Acetylpromazine caused profound decreases in lamellar glucose and L:P, with increased L:G and pyruvate, but did not affect urea clearance or any skin dialysate values.


CONCLUSIONS
Significant changes in microdialysis urea clearance only occurred with severe lamellar hypoperfusion. However, changes in dialysate metabolite concentrations reflected less profound fluctuations in perfusion. This method may be useful for examining lamellar perfusion and energy balance during laminitis development and for the evaluation of vasoactive therapeutics.
Australian Equine Laminitis Research Unit, School of Veterinary Science, The University of Queensland, Gatton, Australia.
C E
CE
Medina-Torres
Australian Equine Laminitis Research Unit, School of Veterinary Science, The University of Queensland, Gatton, Australia.
C
C
Underwood
Australian Equine Laminitis Research Unit, School of Veterinary Science, The University of Queensland, Gatton, Australia.
C C
CC
Pollitt
Australian Equine Laminitis Research Unit, School of Veterinary Science, The University of Queensland, Gatton, Australia.
E M
EM
Castro-Olivera
Australian Institute for Bioengineering and Nanotechnology (AIBN), The University of Queensland, Brisbane St Lucia, Australia.|Metabolomics Australia - Queensland Node, AIBN, The University of Queensland, Brisbane St Lucia, Australia.
M P
MP
Hodson
New Bolton Center, Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, USA.
D W
DW
Richardson
Australian Equine Laminitis Research Unit, School of Veterinary Science, The University of Queensland, Gatton, Australia. a.vaneps@uq.edu.au.
A W
AW
van Eps
D000075:Acepromazine / Q000494:pharmacology; D000818:Animals; D001783:Blood Flow Velocity / Q000662:veterinary*; D004734:Energy Metabolism / Q000502:physiology*; D005528:Foot / Q000098:blood supply*; D005947:Glucose / Q000378:metabolism; D006736:Horses / Q000502:physiology*; D019344:Lactic Acid; D017551:Microdialysis / Q000662:veterinary*; D009638:Norepinephrine / Q000008:administration & dosage / Q000494:pharmacology; D011189:Potassium Chloride / Q000008:administration & dosage / Q000494:pharmacology; D014111:Tourniquets / Q000662:veterinary; D014508:Urea / Q000008:administration & dosage / Q000494:pharmacology
D019344:Lactic Acid; D000075:Acepromazine; D011189:Potassium Chloride; D014508:Urea; D005947:Glucose; D009638:Norepinephrine
bioenergetic; horse; laminitis; metabolite; microdialysis