Pimobendan improves right ventricular myocardial contraction and attenuates pulmonary arterial hypertension in rats with monocrotaline-induced pulmonary arterial hypertension

A review on experimental surgical models and anesthetic protocols of heart failure in rats

Heart failure (HF) is a serious health and economic burden worldwide, and its prevalence is continuously increasing. Current medications effectively moderate the progression of symptoms, and there is a need for novel preventative and reparative treatments. The development of novel HF treatments requires the testing of potential therapeutic procedures in appropriate animal models of HF. During the past decades, murine models have been extensively used in fundamental and translational research studies to better understand the pathophysiological mechanisms of HF and develop more effective methods to prevent and control congestive HF. Proper surgical approaches and anesthetic protocols are the first steps in creating these models, and each successful approach requires a proper anesthetic protocol that maintains good recovery and high survival rates after surgery. However, each protocol may have shortcomings that limit the study's outcomes. In addition, the ethical regulations of animal welfare in certain countries prohibit the use of specific anesthetic agents, which are widely used to establish animal models. This review summarizes the most common and recent surgical models of HF and the anesthetic protocols used in rat models. We will highlight the surgical approach of each model, the use of anesthesia, and the limitations of the model in the study of the pathophysiology and therapeutic basis of common cardiovascular diseases.

Pharmacokinetics of pimobendan following oral administration to New Zealand White rabbits (Oryctolagus cuniculus)

OBJECTIVE

To determine the pharmacokinetics and potential adverse effects of pimobendan after oral administration in New Zealand White rabbits (Ocytolagus cuniculi).

ANIMALS

10 adult sexually intact (5 males and 5 females) rabbits.

PROCEDURES

2 pilot studies were performed with a pimobendan suspension or oral tablets. Eight rabbits received 7.5 mg of pimobendan (mean 2.08 mg/kg) suspended in a critical care feeding formula. Plasma concentrations of pimobendan and O-demethylpimobendan (ODMP) were measured, and pharmacokinetic parameters were calculated for pimobendan by noncompartmental analysis. Body weight, food and water consumption, mentation, urine, and fecal output were monitored.

RESULTS

Mean ± SD maximum concentration following pimobendan administration was 15.7 ± 7.54 ng/mL and was detected at 2.79 ± 1.25 hours. The half-life was 3.54 ± 1.32 hours. Plasma concentrations of pimobendan were detectable for up to 24 hours. The active metabolite, ODMP, was detected in rabbits for 24 to 36 hours. An adverse event occurred following administration of pimobendan in tablet form in 1 pilot study, resulting in death secondary to aspiration. No other adverse events occurred.

CLINICAL RELEVANCE

Plasma concentrations of pimobendan were lower than previously reported for dogs and cats, despite administration of higher doses, and had longer time to maximum concentration and half-life. Based on this study, 2 mg/kg of pimobendan in a critical care feeding formulation should maintain above a target plasma concentration for 12 to 24 hours. However, further studies evaluating multiple-dose administration as well as pharmacodynamic studies and clinical trials in rabbits with congestive heart failure are needed to determine accurate dose and frequency recommendations.

Acute effects of intravenous pimobendan administration in dog models of chronic precapillary pulmonary hypertension

INTRODUCTION

Pulmonary hypertension (PH) is a progressive and potentially life-threatening disease. Several drugs are used for the treatment of dogs with precapillary PH. Pimobendan is an inotropic drug with phosphodiesterase 3 inhibitory and calcium-sensitizing effects. Pimobendan administration improved right ventricular (RV) function and lowered pulmonary arterial pressure in some human patients with precapillary PH. However, the efficacy of pimobendan in dogs with precapillary PH is unknown.

ANIMALS, MATERIAL, AND METHODS

An implantable port device was percutaneously placed in the cranial vena cava of five laboratory beagles. Chronic embolic precapillary PH was induced via the repeated injection of microspheres every 1-2 days. Microsphere injection was continued until systolic pulmonary arterial pressure reached 50 mmHg. Right heart catheterization and echocardiography were performed at baseline and after injections of placebo and pimobendan (0.15 mg/kg).

RESULTS

Repeated injections of microspheres caused an increase in pulmonary vascular resistance, a decrease in stroke volume, RV dilation, left ventricular (LV) and RV dysfunction, and RV dyssynchrony as assessed using echocardiography. Compared with placebo, pimobendan improved LV and RV function based on the LV Tei index from 0.48 to 0.38 (p=0.002) and the RV Tei index from 0.76 to 0.61 (p=0.008), as well as the stroke volume index from 29.4 to 36.7 ml/m² (p=0.012), respectively.

CONCLUSIONS

In dog models of chronic PH, intravenous pimobendan effectively improved RV and LV function and increased stroke volume. However, pimobendan administration did not decrease pulmonary arterial pressure or produce hypotension.

Effects of Single Drug and Combined Short-term Administration of Sildenafil, Pimobendan, and Nicorandil on Right Ventricular Function in Rats With Monocrotaline-induced Pulmonary Hypertension

This study was designed to assess the progression of pulmonary arterial hypertension (PAH) and the effectiveness of therapy using recently investigated echocardiographic parameters. PAH is characterized by the progressive elevation of pulmonary artery pressure and right ventricular hypertrophy and dysfunction, which ultimately results in right-sided heart failure and death. Echocardiography results and invasive measurements of right and left ventricular systolic pressures were compared after 3-week administrations of sildenafil (S group), pimobendan (P group), nicorandil (N group), and their combinations (SP and SPN groups) in male rats with monocrotaline (MCT)-induced pulmonary hypertension (M group) and without this condition (C group). The groups that received pimobendan alone and in combinations (SP and SPN groups) showed improvement in their echocardiographic parameters of systolic function. A significant improvement of diastolic function was achieved in the SPN group. Invasive measurements showed the most significant decreases of right ventricular systolic pressure in the N and SPN groups, and the use of pimobendan resulted in a comparatively low risk of adverse hemodynamic effects (left ventricular systolic pressure). Although our results suggested the attenuation of PAH severity in all treatment groups, PAH could not be reversed.