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

Abstract

BackgroundInsulin resistance (IR) in humans is related to hypertension and impaired vasodilation. Insulin administration has been shown to lower blood pressure both in insulin resistant as well as in insulin sensitive individuals. The aim of the study was to investigate the association between insulin sensitivity and alterations in blood pressure in healthy horses before and after a euglycemic-hyperinsulinemic clamp (EHC). A 3-h EHC was performed in 13 healthy horses (11 mares, 2 geldings). Blood samples for measurement of plasma glucose and insulin were collected before the start of the EHC, every 10 min during the EHC and immediately after the EHC. Mean, systolic- and diastolic blood pressure was measured before and during the final 10 min of the EHC using an indirect high-definition oscillometric monitor (HDO, horse model) applied to the middle of the coccygeal artery. Five consecutive measurements were made in each horse and on each occasion. Insulin and glucose data from the EHC were used to calculate the mean rate of glucose disposal per unit of insulin during steady state (M/I ratio). Insulin resistance was defined as a M/I ratio <5 mg/kg/min/mUL (Lindåse et al. in Am J Vet Res 77:300–309, 2016).ResultsInsulin administration decreased systolic, diastolic and mean arterial pressure in all horses. The M/I ratio for all horses was negatively correlated with the decrease in systolic blood pressure (r2 = 0.55, P = 0.004) and mean arterial pressure (r2 = 0.31, P = 0.048) but not diastolic blood pressure (r2 = 0.12, P = 0.26). Eight horses were defined as insulin resistant (IR) and five horses had normal insulin sensitivity. The five horses with normal insulin sensitivity showed a greater decrease in systolic blood pressure (−17.0 ± 7.4 vs. −3.4 ± 4.6 mmHg, P = 0.001) and MAP (19.2 ± 14.7 vs. 6.9 ± 8.7 mmHg, P = 0.04) than IR horses. There was no difference in the decrease in diastolic blood pressure between groups (16 ± 12.8 vs. 8.9 ± 12.1 mmHg, P = 0.17).ConclusionsThis study indicates that there is a relationship between insulin sensitivity and systolic and MAP in horses. However, studies on a larger number of horses are needed to confirm this association.

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

“…the change in blood pressure was different depending on whether the horse was defined as EMS or control. This suggests an altered response to the cardiovascular effects of insulin in EMS horses compared with control which is in agreement with results from a previous study in horses with varying degrees of insulin sensitivity where a negative linear relationship was found between insulin sensitivity and the degree of decrease in blood pressure during insulin infusion [14]. No differences were seen in resting blood pressure between EMS and control horses.…”

“…It is therefore possible that a difference in basal blood pressure might have been detected if we had studied Shetland ponies. However, together with findings from other studies in ponies the current results strengthen the evidence that EMS, as in human patients, is associated with cardiovascular dysregulation .…”

“…Insulin administration causes vasodilation and lowers systemic blood pressure both in human patients with normal insulin sensitivity as well as in those with insulin resistance, but the vasodilatory effect is blunted in insulin-resistant individuals [10][11][12][13]. Similar findings have been seen in horses where blood pressure was measured before and after a euglycaemic hyperinsulinaemic clamp (EHC), where horses with reduced insulin sensitivity decreased less in blood pressure [14]. This study was performed on horses with reduced insulin sensitivity, but that were not classified to have EMS.…”

“…The current EMS horses were obese and the association between obesity, insulin resistance and hypertension is well established in human patients. The relationship between obesity and insulin resistance in horses is not as clear as in human patients although some breeds seem to be more prone to develop insulin resistance when they are obese [14,16]. There is also evidence that equine blood pressure increases with weight gain despite normal insulin sensitivity [28].…”

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

“…Moreover, insulin stimulates the renin‐angiotensin‐aldosterone system, inducing increased renal sodium reabsorption and blood volume expansion 6,7 . There are indications that the vasodilator pathway is suppressed during insulin resistant (IR) states, whereas the vasoconstrictor pathway is intact or heightened, 5,8‐10 leading to diminished variability in the BP response because of limited vasodilatory capacity, as illustrated by the effect of insulin infusion on BP during an euglycemic hyperinsulinemic clamp (EHC) in IR horses 11,12 . Systolic, diastolic (DBP), and mean arterial blood pressure of control horses decreased gradually during the EHC, whereas obese EMS‐horses experienced no decrease 11 and normal weight IR horses experienced less decrease than did controls, 12 indicating a decreased vasodilatory response in IR horses.…”