Evaluation of fasting plasma insulin and proxy measurements to assess insulin sensitivity in horses

BackgroundProxies are mathematical calculations based on fasting glucose and/or insulin concentrations developed to allow prediction of insulin sensitivity (IS) and beta -cell response. These proxies have not been evaluated in horses with insulin dysregulation. The first objective of this study was to evaluate how fasting insulin (FI) and proxies for IS (1/Insulin, reciprocal of the square root of insulin (RISQI) and the quantitative insulin sensitivity check index (QUICKI)) and beta -cell response (the modified insulin-to-glucose ratio (MIRG) and the homeostatic model assessment of beta -cell function (HOMA-beta)) were correlated to measures of IS (M index) using the euglycemic hyperinsulinemic clamp (EHC) in horses with insulin resistance (IR) and normal IS. A second objective was to evaluate the repeatability of FI and proxies in horses based on sampling on consecutive days. The last objective was to investigate the most appropriate cut-off value for the proxies and FI.ResultsThirty-four horses were categorized as IR and 26 as IS based on the M index. The proxies and FI had coefficients of variation (CVs)= 0.89). All proxies and FI were good predictors of the M index (r=0.76-0.85; P9.5 mu IU/mL for FI.ConclusionsAll proxies and FI provided repeatable estimates of horses' IS. However, there is no advantage of using proxies instead of FI to estimate IR in the horse. Due to the heteroscedasticity of the data, proxies and FI in general are more suitable for epidemiological studies and larger clinical studies than as a diagnostic tool for measurement of IR in individual horses

Radiographic parameters for diagnosing sand colic in horses

<p>Abstract</p> <p>Background</p> <p>Ingestion of sand can cause colic, diarrhoea and weight loss in horses, but these signs are unspecific and can have many other causes. The amount of sand that induces disease may vary between individuals. To avoid over-diagnosing, it is important to determine the amount of sand that can be found in horses without clinical signs of gastrointestinal disease. The aim of this study was to use previously suggested parameters for establishing a radiographic diagnosis of sand colic, and compare these findings between a sand colic group and a control group.</p> <p>Methods</p> <p>Abdominal radiographs were obtained in 30 horses with a complaint unrelated to the gastrointestinal tract. In addition, archived abdominal radiographs of 37 clinical cases diagnosed with sand impaction were investigated. The size of the mineral opacity indicative of sand in the abdomen was measured and graded according to a previously published protocol based on height and length. Location, homogeneity, opacity and number of sand accumulations were also recorded.</p> <p>Results</p> <p>Twenty out of 30 control horses (66%) had one or more sand accumulations. In the present study; height, length and homogeneity of the accumulations were useful parameters for establishing a diagnosis of sand colic. Radiographically defined intestinal sand accumulation grades of up to 2 was a common finding in horses with no clinical signs from the gastrointestinal tract whereas most of the clinical cases had much larger grades, indicating larger sand accumulations.</p> <p>Conclusion</p> <p>Further work to establish a reliable grading system for intestinal sand content is warranted, but a previously proposed grading system based on measurements of height and length may be an alternative for easy assessment of sand accumulations in the meantime. The present study indicates that a grade 1 – 2 sand accumulation in the intestine is a frequent finding in horses. When working up a case with clinical signs from the gastrointestinal tract, one or more accumulations of this grade should not be considered the cause until other possibilities have been ruled out.</p

Repeated post-exercise administration with a mixture of leucine and glucose alters the plasma amino acid profile in Standardbred trotters

<p>Abstract</p> <p>Background</p> <p>The branched chain amino acid leucine is a potent stimulator of insulin secretion. Used in combination with glucose it can increase the insulin response and the post exercise re-synthesis of glycogen in man. Decreased plasma amino acid concentrations have been reported after intravenous or per oral administration of leucine in man as well as after a single per oral dose in horses. In man, a negative correlation between the insulin response and the concentrations of isoleucine, valine and methionine have been shown but results from horses are lacking. This study aims to determine the effect of repeated per oral administration with a mixture of glucose and leucine on the free amino acid profile and the insulin response in horses after glycogen-depleting exercise.</p> <p>Methods</p> <p>In a crossover design, after a glycogen depleting exercise, twelve Standardbred trotters received either repeated oral boluses of glucose, 1 g/kg body weight (BW) at 0, 2 and 4 h with addition of leucine 0.1 g/kg BW at 0 and 4 h (GLU+LEU), or repeated boluses of water at 0, 2 and 4 h (CON). Blood samples for analysis of glucose, insulin and amino acid concentrations were collected prior to exercise and over a 6 h post-exercise period. A mixed model approach was used for the statistical analyses.</p> <p>Results</p> <p>Plasma leucine, isoleucine, valine, tyrosine and phenylalanine concentrations increased after exercise. Post-exercise serum glucose and plasma insulin response were significantly higher in the GLU+LEU treatment compared to the CON treatment. Plasma leucine concentrations increased after supplementation. During the post-exercise period isoleucine, valine and methionine concentrations decreased in both treatments but were significantly lower in the GLU+LEU treatment. There was no correlation between the insulin response and the response in plasma leucine, isoleucine, valine and methionine.</p> <p>Conclusions</p> <p>Repeated post-exercise administration with a mixture of leucine and glucose caused a marked insulin response and altered the plasma amino acid profile in horses in a similar manner as described in man. However, the decreases seen in plasma amino acids in horses seem to be related more to an effect of leucine and not to the insulin response as seen in man.</p

Environmental Levels of the Antiviral Oseltamivir Induce Development of Resistance Mutation H274Y in Influenza A/H1N1 Virus in Mallards

Oseltamivir (Tamiflu®) is the most widely used drug against influenza infections and is extensively stockpiled worldwide as part of pandemic preparedness plans. However, resistance is a growing problem and in 2008–2009, seasonal human influenza A/H1N1 virus strains in most parts of the world carried the mutation H274Y in the neuraminidase gene which causes resistance to the drug. The active metabolite of oseltamivir, oseltamivir carboxylate (OC), is poorly degraded in sewage treatment plants and surface water and has been detected in aquatic environments where the natural influenza reservoir, dabbling ducks, can be exposed to the substance. To assess if resistance can develop under these circumstances, we infected mallards with influenza A/H1N1 virus and exposed the birds to 80 ng/L, 1 µg/L and 80 µg/L of OC through their sole water source. By sequencing the neuraminidase gene from fecal samples, we found that H274Y occurred at 1 µg/L of OC and rapidly dominated the viral population at 80 µg/L. IC50 for OC was increased from 2–4 nM in wild-type viruses to 400–700 nM in H274Y mutants as measured by a neuraminidase inhibition assay. This is consistent with the decrease in sensitivity to OC that has been noted among human clinical isolates carrying H274Y. Environmental OC levels have been measured to 58–293 ng/L during seasonal outbreaks and are expected to reach µg/L-levels during pandemics. Thus, resistance could be induced in influenza viruses circulating among wild ducks. As influenza viruses can cross species barriers, oseltamivir resistance could spread to human-adapted strains with pandemic potential disabling oseltamivir, a cornerstone in pandemic preparedness planning. We propose surveillance in wild birds as a measure to understand the resistance situation in nature and to monitor it over time. Strategies to lower environmental levels of OC include improved sewage treatment and, more importantly, a prudent use of antivirals

Proglycogen and macroglycogen in equine skeletal muscle

The first aim of the present thesis was to establish a method for determination of proglycogen (PG) and macroglycogen (MG) in equine skeletal muscle. The measurement technique for determination of PG and MG was accurate and gave reproducible results. There was an excellent correlation for total glycogen determined in muscle biopsy specimens between the new PG and MG technique and the traditional acid hydrolysis method. A further aim was to examine the degradation of PG and MG in Standardbreds during a maximal exercise test. Horses performed an incremental maximal treadmill exercise test in one-minute steps until they no longer could keep pace with the treadmill. The exercise test induced an anaerobic metabolic response as demonstrated by decreased glycogen, ATP and creatine phosphate and increased lactate in muscle after exercise. The two fractions of glycogen contributed equally to glycogenolysis, 48% and 52% of total glycogen degradation for PG and MG respectively. A study was also performed to determine the degradation and resynthesis of PG and MG in skeletal muscle after intermittent exercise on a slope. At a training camp well trained Standardbreds performed a training session comprising a warm up period, seven repeated 500 m bouts of uphill exercise and a recovery period. Muscle biopsies were taken at rest, at the end of exercise and 1, 4, 8, 24, 48 and 78 hours post exercise. The exercise caused degradation in MG that was twice as large as for PG. The rate of glycogen resynthesis during 1 to 24 hours post exercise was higher for MG than PG. The rate of muscle glycogen synthesis thereafter was slower and did not differ between MG and PG up to 72 hours. The last study was conducted in order to determine PG, MG, glucose and glucose-6-phosphate (G-6-P) in skeletal muscle of horses with polysaccharide storage myopathy (PSSM) before and after light exercise. Horses with PSSM completed repeated intervals of 2 minutes of walking followed by 2 minutes of trotting until muscle cramping developed. Untrained control horses performed a similar exercise test for up to 20 minutes. Before exercise muscle glycogen concentrations were 1.5, 2.2 and 1.7 times higher for PG, MG and total glycogen respectively in PSSM horses compared to control horses. No changes in total glycogen, PG, MG, G-6-P and lactate were found after exercise. However, free glucose concentration increased in skeletal muscle in PSSM horses after exercise indicating that glucose uptake in skeletal muscle is augumented after light exercise

Variability, repeatability and test-retest reliability of equine flash visual evoked potentials (FVEPs)

Background Visual evoked potentials (VEPs) are electrical potentials generated by neurons in the central nervous system in response to visual stimuli. A series of positive and negative wavelets in response to flash-stimuli (flash-VEP; FVEP) or reversing, iso-luminant patterns (pattern-VEP; PVEP) are recorded. Pathological conditions affecting the post-retinal pathways can alter overall waveform morphology, and also affect wavelet peak times and amplitudes. FVEPs have recently been described in horses, but more data on the variability within and between subjects is required, to adequately interpret results from clinical equine patients. Therefore, the purpose of this study was to describe the variability, repeatability and test-retest reliability of equine FVEPs in normal, adult horses.ResultsEquine FVEPs were recorded from one randomly selected eye in 17 horses, from both eyes in eight of these horses, and also at two separate recording sessions in six horses. N1, P2, N2 and P4 wavelets were present in 100% of the recordings in all horses, while P1, N2a, P3 and P5 were only present in some recordings. Coefficients of variation (CVs) were low for P2, N2 and P4 peak times, but higher for all amplitudes. There were no statistically significant differences comparing peak times and amplitudes between eyes or between sessions. Coefficients of repeatability (CRs) are reported for P2, N2 and P4 peak times between eyes (P2; 5ms, N2; 18ms, P4; 18ms) and also between sessions (P2; 5ms, N2; 16ms, P4; 39ms). Intraclass correlation coefficients (ICCs), as an estimate of test-retest reliability, was assessed to be fair to excellent for most parameters. Conclusions This study provides important data on variability, repeatability and test-retest reliability of FVEPs in normal, adult horses. We conclude that P2, N2 and P4 peak times should be included in the evaluation of equine FVEPs. The large inherent variability of FVEP amplitudes is likely to make them less suitable and useful for establishing a diagnosis on their own in most clinical patients, but they may occasionally provide support to a clinical diagnosis

A modified oral sugar test for evaluation of insulin and glucose dynamics in horses

Background: An oral sugar test (OST) using Karo (R) Light Corn Syrup has been developed in the USA as a field test for the assessment of insulin dysregulation in horses but the syrup is not available in Scandinavian grocery stores. The aim of the study was to compare the results of a modified OST between horses with equine metabolic syndrome (EMS) and healthy horses using a Scandinavian commercially available glucose syrup (Dansukker glykossirap). In addition, the effect of breed and the repeatability of the test were evaluated. In the present study, clinically healthy horses (7 Shetland ponies, 8 Icelandic horses, 8 Standardbred horses) and 20 horses of various breeds with EMS underwent the modified OST test. The Icelandic horses and Shetland ponies underwent the OST twice. Insulin and glucose data from the OST were used to calculate peak insulin concentration (Peak(INS)), time to peak insulin concentration (T-peak(INS)), area under the curve for insulin (AUC(INS)) and glucose (AUC(GLU)) as well as whole body insulin sensitivity index (ISICOMP). Results: Compared to the healthy group, the EMS group had 6-7 times higher geometric mean for Peak(INS) and AUC(INS) and 8 times lower geometric mean for ISICOMP. The EMS group had a delayed T-peak(INS) compared to the healthy group. There was no effect of breed in the group of healthy horses on Peak(INS), T-peak(INS), AUC(INS), AUC(GLU) and ISICOMP. Coefficient of variation for repeated tests was 19.8, 19.0 and 17.6 % for Peak(INS), AUC(INS) and ISICOMP respectively. Conclusions: The results of the present study demonstrate that the modified OST appears to be a practical and useful diagnostic tool for assessment of insulin dysregulation in the horse. However, to make it possible to establish the most appropriate sampling interval and to evaluate the accuracy of the modified OST, further studies in horses with a variable degree of insulin resistance are needed, where results from the modified OST are compared with quantitative measurements for IS

Short-term effects of canagliflozin on glucose and insulin responses in insulin dysregulated horses: A randomized, placebo-controlled, double-blind, study

Background Decreasing hyperinsulinemia is crucial in preventing laminitis in insulin dysregulated (ID) horses. Complementary pharmacological treatments that efficiently decrease postprandial hyperinsulinemia in ID horses are needed.Objectives Compare short-term effects of canagliflozin vs placebo on glucose and insulin responses to an oral sugar test (OST) as well as the effects on body weight and triglyceride concentrations in horses with ID.Animals Sixteen privately-owned ID horses.Methods A single-center, randomized, double-blind, placebo-controlled, parallel design study. The horses were randomized (ratio 1:1) to either once daily PO treatment with 0.6 mg/kg canagliflozin or placebo. The study consisted of an initial 3-day period for obtaining baseline data, a 3-week double-blind treatment period at home, and a 3-day follow-up period similar to the initial baseline period but with continued double-blind treatment. Horses were subjected to an 8-sample OST in the morning of the third day on both visits.Results Maximal geometric least square (LS) mean insulin concentration (95% confidence interval [CI]) during the OST decreased after 3 weeks of canagliflozin treatment compared with placebo (83.2; 55.4-125.0 vs 215.2; 143.2-323.2 mu IU/mL). The geometric LS mean insulin response (insulin AUC(0-180)) for canagliflozin-treated horses was >66% lower compared with placebo. Least square mean body weight decreased by 11.1 (4-18.1) kg and LS mean triglyceride concentrations increased by 0.99 (0.47-1.5) mmol/L with canagliflozin treatment.Conclusions and Clinical ImportanceCanagliflozin is a promising drug for treatment of ID horses that requires future studies

Relationship Between β-cell Response and Insulin Sensitivity in Horses based on the Oral Sugar Test and the Euglycemic Hyperinsulinemic Clamp

Background: A hyperbolic relationship between beta-cell response and insulin sensitivity (IS) has been described in several species including rodents, dogs, and humans. This relationship has not been elucidated in the horse. Hypothesis/Objectives: To determine whether the hyperbolic relationship between beta-cell response and IS exists in horses by using indices of beta-cell response from the oral sugar test (OST) and IS measurements from the euglycemic hyperinsulinemic clamp (EHC). A second aim was to compare how well IS estimates from the OST and EHC correlate. Animals: Forty-nine horses with different degrees of insulin regulation (normal-to-severe insulin dysregulation). Methods: Cross-sectional study. Horses were examined with an OST and an EHC. Results: Decreased IS was associated with increased beta-cell response in the horses. Nine of 12 comparisons between indices of beta-cell response and IS measures fulfilled the criteria for a hyperbolic relationship. Indices of IS calculated from the OST correlated highly with the insulin-dependent glucose disposal rate (M) and the insulin-dependent glucose disposal rate per unit of insulin (M/I) determined from the EHC (r = 0.81-0.87). Conclusions and Clinical Importance: A hyperbolic relationship between beta-cell response and IS exists in horses, which suggest that horses with insulin dysregulation respond not only with postprandial hyperinsulinemia but are also insulin resistant. The OST is primarily a test for beta-cell response rather than a test for IS, but calculated indices of IS from the OST may be useful to estimate IS in horses, especially when the horse is insulin resistant