Interday variation and effect of transportation on indirect blood pressure measurements, plasma endothelin-1 and serum cortisol in Standardbred and Icelandic horses

An endothelial regulatory module links blood pressure regulation with elite athletic performance

The control of transcription is crucial for homeostasis in mammals. A previous selective sweep analysis of horse racing performance revealed a 19.6 kb candidate regulatory region 50 kb downstream of the Endothelin3 (EDN3) gene. Here, the region was narrowed to a 5.5 kb span of 14 SNVs, with elite and sub-elite haplotypes analyzed for association to racing performance, blood pressure and plasma levels of EDN3 in Coldblooded trotters and Standardbreds. Comparative analysis of human HiCap data identified the span as an enhancer cluster active in endothelial cells, interacting with genes relevant to blood pressure regulation. Coldblooded trotters with the sub-elite haplotype had significantly higher blood pressure compared to horses with the elite performing haplotype during exercise. Alleles within the elite haplotype were part of the standing variation in pre-domestication horses, and have risen in frequency during the era of breed development and selection. These results advance our understanding of the molecular genetics of athletic performance and vascular traits in both horses and humans.

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.

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.

Does road transport influence plasma leptin concentrations in horses? Preliminary study

Transport is one of the most common stressors for horses leading to an increase in cortisol secretion. Cortisol promotes leptin synthesis and release. The aim of the study was to evaluate the effect of short transport on circulating leptin and cortisol concentrations. A total of 16 crossbred naïve horses (7 geldings, 9 mares) aged 2-11 years, and weighing 530-680 kg were included in the study. The horses were transported in a commercial horse-truck to an unknown holding pen for temporary housing. To measure plasma leptin and cortisol concentrations, three blood samples were collected from each horse: before transport, immediately after unloading from the truck, and nine hours after transport at the arrival point. Transport caused a significant increase in mean plasma cortisol concentration determined at unloading, and after nine hours of unloading, in comparison to values obtained before loading. Plasma leptin concentrations did not change during the study. In conclusion, transportation procedures did not influence plasma leptin concentration in horses, despite significantly increased cortisol release.

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

Background

Insulin 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).

Results

Insulin 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).

Conclusions

This 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.

Effect of Breed on Plasma Endothelin-1 Concentration, Plasma Renin Activity, and Serum Cortisol Concentration in Healthy Dogs

BACKGROUND

There are breed differences in several blood variables in healthy dogs.

OBJECTIVE

Investigate breed variation in plasma endothelin-1 (ET-1) concentration, plasma renin activity, and serum cortisol concentration.

ANIMALS

Five-hundred and thirty-one healthy dogs of 9 breeds examined at 5 centers (2-4 breeds/center).

METHODS

Prospective observational study. Circulating concentrations of ET-1 and cortisol, and renin activity, were measured using commercially available assays. Absence of organ-related or systemic disease was ensured by thorough clinical investigations, including blood pressure measurement, echocardiography, ECG, blood and urine analysis.

RESULTS

Median ET-1 concentration was 1.29 (interquartile range [IQR], 0.97-1.82) pg/mL, median cortisol concentration 46.0 (IQR, 29.0-80.8) nmol/L, and median renin activity 0.73 (IQR, 0.48-1.10) ng/mL/h in all dogs. Overall, breed differences were found in ET-1 and cortisol concentrations, and renin activity (P < .0001 for all). Pair-wise comparisons between breeds differed in 67% of comparisons for ET-1, 22% for cortisol, and 19% for renin activity, respectively. Within centers, breed differences were found at 5/5 centers for ET-1, 4/5 centers for cortisol, and 2/5 centers for renin activity. Newfoundlands had highest median ET-1 concentration, 3 times higher than Cavalier King Charles Spaniels, Doberman Pinschers, and Dachshunds. Median renin activity was highest in Dachshunds, twice the median value in Newfoundlands and Boxers. Median cortisol concentration was highest in Finnish Lapphunds, almost 3 times higher than in Boxers.

CONCLUSIONS AND CLINICAL IMPORTANCE

Breed variation might be important to take into consideration when interpreting test results in clinical studies.