The effect of insulin infusion on heart rate and systemic blood pressure in horses with equine metabolic syndrome

The impact of short-term transportation stress on insulin and oral sugar responses in insulin dysregulated and non-insulin dysregulated horses

BACKGROUND

It is unknown whether short-term transportation affects endocrine responses similarly in horses with and without insulin dysregulation (ID).

OBJECTIVES

To characterise the effect of short-term transportation on stress parameters and insulin responses to an oral sugar test (OST) in horses with and without ID.

STUDY DESIGN

Longitudinal cohort study.

METHODS

Fourteen adult non-pregnant, non-PPID mares of mixed light breeds were grouped as either ID (n = 7) or non-ID (n = 7) based on endocrine testing. Over 2 weeks, horses were transported once, in groups of 3-4 in a horse trailer on a round-trip journey of ~1.5 h. Blood and saliva were collected 24 h and 1 h pre-transportation, directly after unloading and 15 min, 1 h, 3 h plus 24 h post-transportation. An OST was performed 24 h pre-transportation and 3 h post-transportation with a pre- (T0) and post-OST sample collected 60 min later (T60). Heart rates and rectal temperatures were also collected throughout the study. Serum insulin, serum cortisol, and plasma glucose were measured using validated assays. Repeated measures ANOVA were used to determine differences after transportation and between ID and non-ID horses. Non-normal data were log-transformed and multiple comparisons were adjusted using Bonferroni post hoc tests.

RESULTS

Mean insulin was higher in ID horses versus non-ID horses (mean = 109.9 μU/mL vs. 30.2 μU/mL, p < 0.001; 95% CI for mean difference = [55.6-107.7 μU/mL]). Mean serum insulin increased following OST at T60 in ID horses pre- (154.6 μU/mL, p = 0.04; 95% CI = [86.3-223.0 μU/mL]) and post-transportation (284.6 μU/mL, p = 0.03; 95% CI = [114.3-454.8 μU/mL]). Non-ID horses had a mean OST T60 insulin post-transportation of 56.6 μU/mL (95% CI = [29.1-84.1 μU/mL]); above recognised threshold [45 μU/mL] for ID diagnosis.

MAIN LIMITATIONS

Small number of horses, only mares used, and OST not performed immediately post-transportation.

CONCLUSIONS

Performing an OST 3 h following short-term transportation may result in inaccurate ID status.

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 μIU/mL). The geometric LS mean insulin response (insulin AUC0-180 ) 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 IMPORTANCE

Canagliflozin is a promising drug for treatment of ID horses that requires future studies.

A one-health approach to identifying and mitigating the impact of endocrine disorders on human and equine athletes

Endocrinopathies affect multiple species in ever-increasing percentages of their populations, creating an opportunity to apply one-health approaches to determining creative preventative measures and therapies in athletes. Obesity and alterations in insulin and glucose dynamics are medical concerns that play a role in whole-body health and homeostasis in both horses and humans. The role and impact of endocrine disorders on the musculoskeletal, cardiovascular, and reproductive systems are of particular interest to the athlete. Elucidation of both physiologic and pathophysiologic mechanisms involved in disease processes, starting in utero, is important for development of prevention and treatment strategies for the health and well-being of all species. This review focuses on the unrecognized effects of endocrine disorders associated with the origins of metabolic disease; inflammation at the intersection of endocrine disease and related diseases in the musculoskeletal, cardiovascular, and reproductive systems; novel interventions; and diagnostics that are informed via multiomic and one-health approaches. Readers interested in further details on specific equine performance conditions associated with endocrine disease are invited to read the companion Currents in One Health by Manfredi et al, JAVMA, February 2023.

Biological and pharmacological effects and nutritional impact of phytosterols: A comprehensive review

Phytosterols (PSs), classified into plant sterols and stanols, are bioactive compounds found in foods of plant origin. PSs have been proposed to exert a wide number of pharmacological properties, including the potential to reduce total and low-density lipoprotein (LDL) cholesterol levels and thereby decreasing the risk of cardiovascular diseases. Other health-promoting effects of PSs include anti-obesity, anti-diabetic, anti-microbial, anti-inflammatory, and immunomodulatory effects. Also, anticancer effects have been strongly suggested, as phytosterol-rich diets may reduce the risk of cancer by 20%. The aim of this review is to provide a general overview of the available evidence regarding the beneficial physiological and pharmacological activities of PSs, with special emphasis on their therapeutic potential for human health and safety. Also, we will explore the factors that influence the physiologic response to PSs.

Effect of a long-term high-energy diet on cardiovascular parameters in Shetland pony mares

BACKGROUND

Changes in cardiovascular parameters, including blood pressure (BP) and cardiac anatomical dimensions, are an inconsistent feature of the equine metabolic syndrome. The order in which these changes arise is unknown.

OBJECTIVES

Determine the order in which EMS-associated changes in cardiovascular parameters arise.

ANIMALS

Twenty Shetland pony mares.

METHODS

High-energy (HE) diet mares were fed 200% of net energy requirements for 1 (n = 3) or 2 (n = 7) consecutive diet-years, with 17 weeks of hay-only between years. Noninvasive BP measurements and echocardiograms were performed during both years. Resting 24-hour ECGs and measurements of autonomic tone (splenic volume and packed cell volume [PCV]) were performed at the end of diet-year 1. Results were compared to control mares receiving a maintenance diet for 1 (n = 7) or 2 (n = 3) consecutive years.

RESULTS

In year 1, HE mares had significantly higher values than control mares for mean relative left ventricular wall thickness (P = .001). After 2 diet-years, mean systolic (P = .003), diastolic (P < .001) and mean arterial BP (P = .001), heart rate (HR; P < .001), and mean left ventricular wall thickness (P = .001) also were significantly increased in HE compared to control mares. No pathological arrhythmias or differences in splenic volume or PCV were detected.

CONCLUSIONS AND CLINICAL IMPORTANCE

Ingesting a HE diet first induced minor changes in BP, and progressed to left-sided cardiac hypertrophy in Shetland pony mares. These findings are of interest given the increasing incidence of obesity in horses.

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

Background

Proxies are mathematical calculations based on fasting glucose and/or insulin concentrations developed to allow prediction of insulin sensitivity (IS) and β-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 β-cell response (the modified insulin-to-glucose ratio (MIRG) and the homeostatic model assessment of β-cell function (HOMA-β)) 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.

Results

Thirty-four horses were categorized as IR and 26 as IS based on the M index. The proxies and FI had coefficients of variation (CVs) ≤ 25.3 % and very good reliability (intraclass correlation coefficients ≥ 0.89). All proxies and FI were good predictors of the M index (r = 0.76–0.85; P < 0.001). The proxies for IS had a positive linear relationship with the M index whereas proxies for β-cell response and FI had an inverse relationship with the M index. Cut-off values to distinguish horses with IR from horses with normal IS based on the M index were established for all proxies and FI using receiver operating characteristic curves, with sensitivity between 79 % and 91 % and specificity between 85 % and 96 %. The cut-off values to predict IR were < 0.32 (RISQI), < 0.33 (QUICKI) and > 9.5 µIU/mL for FI.

Conclusions

All 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.

Changes in metabolic and physiological biomarkers in Mangalarga Marchador horses with induced obesity

This study aimed to characterize and correlate physiological and metabolic changes in horses fed a hypercaloric diet (HD). Nine mature horses with a mean initial body condition score of 2.9 ± 1 (scale, 1-9) were fed a high-calorie diet for 5 months. Fasting blood samples were collected before the study and biweekly for the duration of the project to determine the concentrations of cholesterol (CHOL), very low (VLDL), low (LDL) and high-density (HDL) lipoproteins, triglycerides, non-esterified fatty acids, and fructosamine. A low-dose oral glucose tolerance test (LGTT) was conducted before, 75 and 150 days after HD introduction. Mean arterial blood pressure was measured monthly. Following HD introduction, CHOL, LDL, HDL, and fructosamine blood concentrations increased (P < 0.001). These four variables were also positively and significantly correlated with the blood insulin response to LGTT. These findings confirm the occurrence of hypercholesterolemia concomitantly with insulin dysregulation development in horses exposed to HD.

The effect of diet-induced obesity and pasture on blood pressure and serum cortisol in Standardbred mares

BACKGROUND

Obesity is associated with insulin resistance, vascular dysfunction and altered cortisol metabolism both in humans and in horses.

OBJECTIVES

Evaluate the effect of weight gain induced by a haylage diet low in nonstructural carbohydrates (NSC) on insulin sensitivity, blood pressure and serum cortisol concentrations.

STUDY DESIGN

In vivo experiment.

METHODS

Nine adult Standardbred mares fed a fat supplemented haylage diet at 250% of the horses' daily metabolisable energy requirements for 22 weeks. Horses were then turned out on pasture for 4 weeks. Insulin sensitivity (SI_CLAMP ) was measured before and after weight gain and after 4 weeks of pasture using the euglycemic hyperinsulinaemic clamp (EHC) method. Body condition score (BCS), blood pressure and serum cortisol were monitored throughout the study. All data were analysed using the linear mixed model procedure. Values of P < 0.05 were considered as statistically different.

RESULTS

All horses became obese during the weight gain period (BCS> 7). Mean arterial blood pressure (MAP) increased during the weight gain period and was significantly higher than initial values at the end of the weight gain period (78 ± 3 mm Hg vs 92 ± 3 mmHg). MAP remained increased on pasture (93 ± 3 mmHg). SI_CLAMP was unaffected by weight gain 0.9 ± 0.1 vs 1.0 ± 0.1 ([mg/kg/min × 10³ ]/[µIU/mL × mmol/L])) but improved after pasture (1.6 ± 0.1 ([mg/kg/min × 10³ ]/ [mU/L]). Serum cortisol concentrations increased during the weight gain period (80 ± 9 nmol/L vs 112 ± 9 nmol/L) and remained increased during pasture.

MAIN LIMITATIONS

Limited number of horses and no control group.

CONCLUSIONS

Obesity was associated with a linear increase in blood pressure and an increase in serum cortisol that was not associated with insulin sensitivity.

Role of Hyperinsulinemia and Insulin Resistance in Hypertension: Metabolic Syndrome Revisited

Hyperinsulinemia and insulin resistance were proposed more than 30 years ago to be important contributors to elevated blood pressure (BP) associated with obesity and the metabolic syndrome, also called syndrome X. Support for this concept initially came from clinical and population studies showing correlations among hyperinsulinemia, insulin resistance, and elevated BP in individuals with metabolic syndrome. Short-term studies in experimental animals and in humans provided additional evidence that hyperinsulinemia may evoke increases in sympathetic nervous system (SNS) activity and renal sodium retention that, if sustained, could increase BP. Although insulin infusions may increase SNS activity and modestly raise BP in rodents, chronic insulin administration does not significantly increase BP in lean or obese insulin-resistant rabbits, dogs, horses, or humans. Multiple studies in humans and experimental animals have also shown that severe insulin resistance and hyperinsulinemia may occur in the absence of elevated BP. These observations question whether insulin resistance and hyperinsulinemia are major factors linking obesity/metabolic syndrome with hypertension. Other mechanisms, such as physical compression of the kidneys, activation of the renin-angiotensin-aldosterone system, hyperleptinemia, stimulation of the brain melanocortin system, and SNS activation, appear to play a more critical role in initiating hypertension in obese subjects with metabolic syndrome. However, the metabolic effects of insulin resistance, including hyperglycemia and dyslipidemia, appear to interact synergistically with increased BP to cause vascular and kidney injury that can exacerbate the hypertension and associated injury to the kidneys and cardiovascular system.