Aldosterone plasma concentration in horses with heart valve insufficiencies

Measurement of plasma endothelin-1 concentration in healthy horses and horses with cardiac disease during rest and after exercise

Cardiac biomarkers are important tools for monitoring disease progress and can monitor progression of therapy. Endothelin-1 (ET-1) has been studied for its use as a cardiac biomarker in human and small animal medicine while in horses with cardiac disease it has not been evaluated yet. The objective of the present study was to determine the concentration of plasma ET-1 in healthy horses and compare it with ET-1 concentration in horses with cardiac disease during rest and after exercise. Fifty four horses admitted to the Equine Clinic of Free University of Berlin were used in the present study, of which 15 horses were clinically healthy with no evidence of cardiac disease (Group 1), 22 horses suffered from cardiac disease with normal heart dimensions (Group 2) and 17 horses with cardiac disease and enlarged heart diameters (Group 3). Clinical examination, electrocardiography and echocardiography were performed. Endothelin-1 concentration was determined using ET-1 ELISA kit. The concentration of plasma ET-1 was significantly increased in horses with cardiac disease and normal cardiac dimensions (Group 2) and in horses with cardiac disease and enlargement of the left atrium (Group 3) compared to its concentration in clinically healthy horses (Group 1). In addition, the concentration of plasma ET-1 after exercise was significantly increased in diseased horses compared to its concentration at rest. Detection of ET-1 plasma concentration in horses at rest may be useful for detecting horses with changes in left atrial cardiac dimensions.

Preliminary investigation of orally administered benazepril in horses with left-sided valvular regurgitation

BACKGROUND

Despite the paucity of data available, orally administered angiotensin-converting enzyme (ACE) inhibitors are empirically used in horses with valvular regurgitation.

OBJECTIVE

Evaluate the echocardiographic and hormonal changes in response to oral benazepril in horses with left-sided valvular regurgitation.

STUDY DESIGN

Prospective, randomised double-blind, placebo-controlled trial.

METHODS

Horses with mitral valve (MR) and/or aortic valve regurgitation (AR) received oral benazepril (n = 6) at a dosage of 1 mg/kg q 12 h or a placebo (n = 5) for 28 days. Echocardiography was performed before drug administration and after 28 days of treatment. Plasma renin activity, serum ACE activity, angiotensin II concentration, aldosterone concentration and biochemical variables were measured before drug administration and after 7 and 28 days of treatment.

RESULTS

Relative to baseline, horses treated with benazepril had statistically significant reduction in left ventricular internal diameter in systole (mean difference between groups = -0.97 cm; 95% CI = -1.5 to -0.43 cm), aortic sinus diameter (-0.31 cm; -0.54 to -0.07 cm), and percentage of the aortic annulus diameter occupied by the base of the AR jet (-17.05%; -31.17 to -2.93%) compared with horses receiving a placebo. In addition, horses treated with benazepril had a significantly greater increase in cardiac output (11.95 L/min; 1.17-22.73 L/min) and fractional shortening (7.59%; 3.3-11.88%) compared with horses receiving a placebo. Despite profound serum ACE inhibition, renin activity and concentrations of angiotensin II and aldosterone were not significantly different between treatment groups or among time points.

MAIN LIMITATIONS

Very small sample size and short treatment period.

CONCLUSIONS

Treatment with oral benazepril resulted in statistically significant echocardiographic changes that might indicate reduced cardiac afterload in horses with left-sided valvular regurgitation. Additional studies with a larger sample size will be necessary to determine if administration of benazepril is beneficial in horses with valvular regurgitation. The Summary is available in Spanish - see Supporting Information.

The heart remains the core: cardiac causes of poor performance in horses compared to human athletes

Cardiac remodelling occurs in response to exercise and is generally beneficial for athletic performance due to the increase in cardiac output. However, this remodelling also may lead to an increased prevalence of cardiac murmurs and arrhythmias. In most cases, these are not considered to be significant. However, in some cases, there may be potentially deleterious consequences. Whilst sudden cardiac death (SCD) is a rare occurrence, the consequences are catastrophic for both the horse and potentially the rider or driver. Furthermore, the sudden death of a horse in the public arena has negative connotations in regards to public perception of welfare during equestrian sports. Prediction of which individuals might be susceptible to potential deleterious effects of exercise is a focus of interest in both human and equine athletes but remains a challenge because many athletes experience cardiac murmurs and exercise-induced arrhythmias that are clinically irrelevant. This review summarises the effects of exercise on cardiac remodelling in the horse and the potential effects on athletic performance and SCD. The use of biomarkers and their future potential in the management of athletic horses is also reviewed.

Pharmacokinetic/pharmacodynamic modeling of benazepril and benazeprilat after administration of intravenous and oral doses of benazepril in healthy horses

Pharmacokinetic and pharmacodynamic (PK/PD) properties of the angiotensin-converting enzyme inhibitor (ACEI) benazeprilat have not been evaluated in horses. This study was designed to establish PK profiles for benazepril and benazeprilat after intravenous (IV) and oral (PO) administration of benazepril using a PK/PD model. This study also aims to determine the effects of benazeprilat on serum angiotensin converting enzyme (ACE), selecting the most appropriate dose that suppresses ACE activity. Six healthy horses in a crossover design received IV benazepril at 0.50mg/kg and PO at doses 0 (placebo), 0.25, 0.50 and 1.00mg/kg. Blood pressures (BP) were measured and blood samples were obtained at different times in order to measure serum drug concentrations and serum ACE activity, using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and spectrophotometry, respectively. Systemic bioavailability of benazeprilat after PO benazepril was 3-4%. Maximum ACE inhibitions from baseline were 99.63% (IV benazepril), 6.77% (placebo) and 78.91%, 85.74% and 89.51% (for the three PO benazepril doses). Significant differences in BP were not found. Although oral availability was low, benazeprilat 1.00mg/kg, reached sufficient serum concentrations to induce long lasting serum ACE inhibitions (between 88 and 50%) for the first 48h. Additional research on benazepril administration in equine patients is indicated.

Attenuation of the blood pressure response to exogenous angiotensin I after oral administration of benazepril to healthy adult horses

BACKGROUND

Benazepril has been shown to inhibit circulating angiotensin-converting enzyme (ACE) activity in horses but the optimal dosage is unknown.

OBJECTIVES

To determine the lowest tested dose of benazepril that results in ≥75% attenuation in the response of arterial blood pressure (BP) to exogenous angiotensin I (ANG-I) administration.

STUDY DESIGN

Prospective experimental study.

METHODS

A total of 5 healthy horses were instrumented for the direct measurement of BP. Each horse received 4 intragastric doses of benazepril (0.5, 1, 2 and 4 mg/kg bwt) with a washout period of 7 days between doses. Prior to and 2, 12 and 24 h after benazepril administration, each horse received intravenous (i.v.) boluses of ANG-I at 20, 60 and 200 ng/kg. Attenuation of the systolic arterial pressure (SBP) response to ANG-I and serum ACE activity were quantified and expressed as percentage of inhibition.

RESULTS

There was a significant effect of benazepril dose (P = 0.004) and time (P = 0.004) on the percentage of inhibition of the systolic pressor response to ANG-I. Regardless of benazepril dose, the percentage of inhibition was significantly greater 2 h after administration of benazepril compared with 12 and 24 h. At an ANG-I dose of 20 ng/kg, the percentage of inhibition after administration of benazepril at 1 mg/kg bwt (46.6 ± 18.9%) was significantly greater than that achieved after 0.5 mg/kg bwt (19 ± 14%) but not significantly different from that achieved at higher doses of benazepril. Benazepril doses ≥1 mg/kg bwt resulted in serum ACE inhibition of at least 90%.

MAIN LIMITATIONS

Small sample size and resulting low statistical power.

CONCLUSIONS

Attenuation of the rise in SBP in response to ANG-I after administration of benazepril is modest in horses despite adequate serum ACE inhibition. A dose of 1 mg/kg bwt would be recommended for future investigations of benazepril for the management of cardiovascular diseases in horses.

Pharmacokinetics and pharmacodynamics of enalapril and its active metabolite, enalaprilat, at four different doses in healthy horses

Pharmacokinetic and pharmacodynamic of IV enalapril at 0.50 mg/kg, PO placebo and PO enalapril at three different doses (0.50, 1.00 and 2.00 mg/kg) were analyzed in 7 healthy horses. Serum concentrations of enalapril and enalaprilat were determined for pharmacokinetic analysis. Angiotensin-converting enzyme (ACE) activity, serum ureic nitrogen (SUN), creatinine and electrolytes were measured, and blood pressure was monitored for pharmacodynamic analysis. The elimination half-lives of enalapril and enalaprilat were 0.67 and 2.76 h respectively after IV enalapril. Enalapril concentrations after PO administrations were below the limit of quantification (10 ng/ml) in all horses and enalaprilat concentrations were below the limit of quantification in 4 of the 7 horses. Maximum mean ACE inhibitions from baseline were 88.38, 3.24, 21.69, 26.11 and 30.19% for IV enalapril at 0.50 mg/kg, placebo and PO enalapril at 0.50, 1.00 and 2.00 mg/kg, respectively. Blood pressures, SUN, creatinine and electrolytes remained unchanged during the experiments.

Adrenocortical insufficiency in horses and foals

The adrenal cortices produce various steroid hormones that play vital roles in several physiologic processes. Although permanent adrenocortical insufficiency is rare in all species, emerging evidence in both human and equine medicine suggests that transient reversible adrenocortical dysfunction resulting in cortisol insufficiency frequently develops during critical illness. This syndrome is termed relative adrenal insufficiency (RAI) or critical illness-related corticosteroid insufficiency (CIRCI) and can contribute substantially to morbidity and mortality associated with the primary disease. This review discusses the mechanisms, diagnosis, and clinical consequences of adrenocortical insufficiency, with particular focus on the current understanding of RAI/CIRCI in horses and foals.