Hyperinsulinaemia increases vascular resistance and endothelin‐1 expression in the equine digit

Abstract

SummaryReasons for performing study: Insulin leads to overexpression of endothelin-1 (ET-1) in the endothelium of insulin-resistant rodents. If this is also the case in equine laminar tissue, this could explain the predisposition of insulin-resistant horses to laminitis. Objectives: To investigate the effect of hyperinsulinaemia on metabolism and vascular resistance of the isolated equine digit in a model of extracorporeal perfusion. Study design: Randomised, controlled study with interventional group, with blinded evaluation of histology results. Method: After exsanguination, equine digits (n = 11) and autologous blood were collected at an abattoir. One digit served as a hyperinsulinaemic pilot limb, 5 digits were assigned to the hyperinsulinaemic perfusion (IP) group and 5 to the control perfusion (CP) group. Digits were perfused for 10 h at a defined perfusion rate of 12 ml/min/kg. After the first hour of perfusion (equilibration period), insulin was added to the reservoir of the IP digits. Perfusion pressure, glucose consumption, lactate and lactate dehydrogenase were monitored. Vascular resistance was calculated as perfusion pressure (in millimetres of mercury) in relation to the flow rate (in millilitres per minute). After perfusion, histology samples of the dorsal hoof wall (haematoxylin & eosin or periodic acid-Schiff) were evaluated. Immunohistology with a polyclonal rabbit-derived anti-endothelin antibody was used for detection of ET-1. Results: In the IP group, the mean insulin concentration in the plasma of the perfusate was 142 Ϯ 81 miu/ml, while insulin concentration was <3 miu/ml in the CP group. Mean vascular resistance was significantly higher (P<0.01) in the IP group (2.04 Ϯ 1.13 mmHg/ml/min) than in the CP group (1.31 Ϯ 0.55 mmHg/ml/min). Histology of the IP group samples showed significantly more vessels with an open lumen, increased width of the secondary epidermal lamellae and formation of oedema. In the lamellar vessels (veins and arteries) and nerve fibres, ET-1 expression was much more prominent in the IP group than in the CP group samples. Conclusions: Short-term hyperinsulinaemia leads to increased vascular resistance in the equine digit and increased expression of ET-1 in the laminar tissue.

Extracorporeal perfusion of isolated organs of large animals – Bridging the gap between in vitro and in vivo studies

“…Insulin increases the activity of the Na + /K + ATPase pump and excess potassium is removed from the extracellular space. However, other effects of insulin should be noted, e.g., change in endothelin-1 expression and associated laminitic changes in the perfused equine digit (Gauff et al, 2013. In the event of acidosis during perfusion experiments, potassium may also move from the intracellular space to the extracellular fluid in an attempt to buffer dropping pH levels (Oster et al, 1978).…”

“…Gauff et al, 2013(Patan-Zugaj et al, 2012 Investigating the role of hyperinsulinemia Hyperinsulinemia alters endothelin-1 in the context of laminitis expression in the equine laminar tissue which suggests endothelin receptor antagonists as a potential new class of agents in the treatment of laminitis (Gauff et al, 2013 Pharmacokinetic studies in Acetylsalicylic acid and salicylic acid Friebe et al, 2013a the context of joint disease accumulate in the synovial fluid after systemic administration, despite subsiding systemic levels (Friebe et al, 2013b) Limb (porcine) Prolonged limb preservation Prolonged limb preservation barely Constantinescu et al, 2011 for transplantation influences ischemia/ reperfusion injury, ECP LA is a promising technique for use in transplantation surgery (Müller et al, 2013) Udder (caprine) Exploring physiological concepts Metabolism of various substrates and Hebb and Linzell, 1951;(milk synthesis) their contribution to milk synthesis Linzell, 1960 (Hardwick, 1965;Roets et al, 1979b, inter alia) …”

Role of insulin during the development of oligofructose (OF)-induced equine laminitis

“…Laminitis can also develop after horses accidentally consume too much grain, thus causing alimentary carbohydrate overload (28). Laminitis caused by carbohydrate-overload is a kind of sepsisrelated laminitis, and the latter has attracted more attention than any other type of laminitis over the past few decades due to the number of available models of this disease induction, including such carbohydrateoverload models as the traditional corn starch/wood flour and the more recent oligofructose (OF) models (6,7). Out of these two, OF reliably induces laminitis (6), and it is currently the best available means of inducing experimental laminitis to mimic exposure to excessive carbohydrates; moreover, it has a reduced incidence of colic and low death rate, compared to the starchinduction model (17).…”

Muscle Mitochondrial Dysfunction in Horses Affected by Acute Laminitis

“…Recently, Gauff et al showed that short-term hyperinsulinaemia in the isolated, perfused extracorporeal equine digit leads to a marked increase in vascular resistance and an increase in endothelin-1 expression [23].…”