Evaluation of field-testing protocols to diagnose insulin dysregulation in ponies using a Bayesian approach

Effect of pergolide treatment on insulin dysregulation in horses and ponies with pituitary pars intermedia dysfunction

BACKGROUND

Due to the high frequency of laminitis reported for both conditions, the relationship between pituitary pars intermedia dysfunction (PPID) and insulin dysregulation (ID), and the potential role of dopamine in modifying insulin secretion, requires further investigation.

OBJECTIVES

To evaluate the effect of pergolide mesylate on insulin sensitivity and postprandial insulin and glucose responses in horses and ponies with ID, both with or without concurrent PPID.

STUDY DESIGN

Randomised crossover study.

METHODS

Sixteen horses and ponies, comprising eight matched pairs (PPID+ID or ID-only), were given pergolide mesylate at a dose of 2 μg/kg bwt orally once daily for 4 weeks (plus a 4-week non-treatment control period, with a 4-week washout between phases). A combined glucose and insulin tolerance test (CGIT) and a standard meal test (SMT; containing 1.1 g/kg bwt of starch and 0.1 g/kg bwt of free sugars), were performed before and after each treatment period to determine insulin sensitivity and postprandial insulin and glucose responses, respectively. Variables derived from the CGIT and SMT were analysed using linear mixed models.

RESULTS

Pergolide treatment did not alter any of the variables derived from the CGIT in either the PPID+ID or ID-only groups (all p > 0.05). For the SMT, insulin responses were reduced by pergolide treatment for the PPID+ID group, with Δ change values for the total area under the curve for insulin over 300 mins (estimated marginal mean [95% confidence interval]) being -25.4 (-39.9 to -7.3) min∙mIU/mL (p = 0.03) and Δ change values for peak insulin concentration being -100 (-167 to -29) μIU/mL (p = 0.04). No effect of pergolide treatment was detected for the ID-only group.

MAIN LIMITATIONS

Number of animals and heterogeneity among groups.

CONCLUSIONS

Pergolide had no effect on tissue insulin sensitivity. However, the results suggest that postprandial hyperinsulinaemia may be limited by this dopamine receptor agonist in animals with PPID plus ID.

Value of measuring markers of lipid metabolism in horses during an oral glucose test

BACKGROUND

Characterizing the lipid response to an oral glucose test (OGT) might improve our understanding of Equine Metabolic Syndrome.

HYPOTHESIS/OBJECTIVES

To describe the effects of an OGT on lipid metabolism and determine the value of measuring triglyceride and nonesterified fatty acid (NEFA) concentrations in hyperinsulinemic (HI) and insulin-resistant (IR) horses.

ANIMALS

Twenty horses including 7 HI-IR horses, 4 HI-non-IR horses, and 9 non-HI-non-IR horses (control).

METHODS

Cross-sectional design. Horses underwent an OGT, with blood samples collected at 0, 60, 90, and 120 minutes. Insulin, glucose, triglyceride, and NEFA concentrations were measured and compared over time and between groups, with P < .05 considered significant.

RESULTS

In all horses, the OGT had a significant effect on triglyceride concentrations (median [interquartile range]: .35 [.30-.50] mmol/L at 0 minute vs .25 [.21-.37] mmol/L at 120 minutes, P = .005) and on NEFA concentrations (.1 [.1-.2] mEq/L at 0 minute vs .05 [.05-.1] mEq/L at 120 minutes, P = .0009). However, horses with HI and IR had higher triglyceride areas under the curve (AUC, 79.46 ± 46.59 vs 33.32 ± 6.75 mmol/L*min, P = .01) as well as NEFA AUC (9.1 ± 2.9 vs 6.0 ± 6.8 mEq/L*min, P = .03) than control horses. No significant difference was detected between control and HI non-IR horses.

CONCLUSIONS AND CLINICAL IMPORTANCE

Determining triglyceride and NEFA concentrations might help assess tissue insulin resistance during an OGT.

Epidemiological investigation of insulin dysregulation in Shetland and Welsh ponies in Australia

BACKGROUND

Insulin dysregulation (ID) is central to equine metabolic syndrome. There are limited epidemiological studies investigating dynamic testing of ID in ponies.

OBJECTIVES

To evaluate prevalence and risk factors for ID through dynamic testing of hyperinsulinaemia (DHI) and insulin resistance (IR).

STUDY DESIGN

Cross-sectional.

METHODS

Sex, age, breed, height, cresty neck score (CNS), body condition score (BCS), laminitis, HMGA2:c.83G>A genotype and pituitary pars intermedia dysfunction (PPID) status were documented. Dynamic hyperinsulinaemia was diagnosed with an oral sugar test (OST) and IR with an insulin tolerance test (ITT). Owners completed surveys reporting activity, laminitis history and perception of body condition using a (1-9) visual analogue scale (VASo). Ordinal scores were converted to binary outcomes for CNS (≤2/5 or ≥3/5), BCS and VASo (≤6/9 or ≥7/9). Variables associated with insulin concentrations, glucose reduction after the ITT and laminitis were evaluated with mixed effects regression models accounting for random effects of farms.

RESULTS

Among 167 ponies tested, median (range) age was 9 (4-21) years and BCS was 6 (4-8). Prevalence (95% confidence interval [CI]) of ID was 61 (53-68)%. Factors associated with insulin concentrations (estimate [95% CI]; μIU/mL) 60 min post-OST were: age (1.07 [1.02-1.11]), CNS (≥3/5, 1.52 [1.04-2.23]) and VASo (≥7/9, 1.75 [1.09-2.79]); and 90 min post-OST were: age (1.08 [1.03-1.12]), CNS (≥3/5, 1.80 [1.22-2.64]), VASo (≥7/9, 2.49 [1.52-4.08]) and sex (male, 0.64 [0.45-0.91]). Factors associated with glucose reduction after the ITT (estimate [95% CI]; %) were: age (-1.34 [-2.01 to -0.67]), sex (female, -6.21 [-11.68 to -0.74]) and VASo (≥7/9, -1.74 [-18.89 to -4.78]). Factors associated with laminitis (odds ratio [95% CI]) were DHI (4.60 [1.68-12.58]), IR (3.66 [1.26-10.61]) and PPID (11.75 [1.54-89.40]).

MAIN LIMITATIONS

Single time-point sampling, laminitis definition and diet analysis.

CONCLUSIONS

Ageing, being female and owner-perceived obesity were associated with ID.