Blood pressure in Warmblood horses before and during a euglycemic-hyperinsulinemic clamp

Hyperinsulinemia negatively affects the association between insulin resistance and blood pressure

BACKGROUND AND AIMS

Although hyperinsulinemia and insulin resistance (IR) together cause metabolic diseases, the available evidence fails to link hyperinsulinemia with blood pressure (BP) elevation. To further understand the role of hyperinsulinemia in the pathophysiology of hypertension, we conducted this study to investigate the moderating effect of fasting insulin (FINS) on the association between IR and BP.

METHODS AND RESULTS

The health screening data of 72,076 individuals were analyzed for this moderation analysis. IR was indicated by the homeostatic model assessment of insulin resistance (HOMA-IR), triglyceride-glucose index (TyG), and triglyceride to high-density lipoprotein cholesterol ratio (TG/HDLc). In the adjusted model, three IR indicators were considered independent variables; FINS was used as a moderator, and systolic BP (SBP) and diastolic BP (DBP) were used as dependent variables. The regression coefficient of the interaction term between the three IR indicators and FINS was significantly negative in all moderation models. Simple slope tests and the Johnson-Neymann technique also indicated that FINS negatively moderated the association between IR and BP.

CONCLUSIONS

This moderation analysis showed that FINS negatively mediated the association between IR and BP, suggesting that hyperinsulinemia may buffer, not reinforce, the effect of IR on hypertension.

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.

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.

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

BACKGROUND

There is little evidence that horses with equine metabolic syndrome (EMS) have higher resting blood pressures than horses with normal insulin sensitivity. However, there are indications that EMS horses have an altered dynamic response to the cardiovascular effects of insulin.

OBJECTIVES

To examine heart rate and the systemic blood pressure response in EMS and control horses during insulin infusion.

STUDY DESIGN

Cross-sectional study.

METHODS

Horses were examined with an oral sugar test (OST) and a euglycaemic hyperinsulinaemic clamp (EHC). Based on the results from the OST, the horses were classified as either EMS or control. Blood pressure was measured before the start of the EHC and at 60, 120 and 180 min of the EHC.

RESULTS

There were 16 EMS and 12 control horses. Mean resting heart rate was higher for EMS horses compared with control (35.6 ± 5.1 vs. 30.3 ± 3.5 beats/min). Systolic, diastolic and mean arterial blood pressure did not differ between groups at the start of the EHC. Blood pressure decreased gradually during the EHC in the control group, whereas the EMS group showed no decline in systolic, diastolic or mean arterial pressure.

MAIN LIMITATIONS

Limited number of horses.

CONCLUSIONS

Horses with EMS have cardiovascular changes that affect resting heart rate and systemic blood pressure during insulin infusion.