Sildenafil increases the force of right atrial contractions in vitro via the NO-guanylyl cyclase pathway involving β-adrenoceptor linked mechanisms

Acute Exposure to Bisphenol S Decreases In Vitro Right Atrial Contractility in Rats

AIM/OBJECTIVE

Bisphenols are widely used in the manufacturing of polycarbonate material and epoxy resins which constitute the essential component of plastic. Bisphenol A (BPA) has been reported to produce toxicity on organs in both animal and human studies. Therefore, plastic manufacturers are replacing BPA with other analogues that are considered to be safe, and BPA-free products are now available in the market. However, some studies have reported that bisphenol-S (BPS) also possesses toxic properties. It has been reported to depress ventricular contraction as well as produce ventricular arrhythmia on acute exposure. The present study was performed to examine the effect of BPS on in vitro spontaneously-beating right atria in rats.

METHODS

In the present study, in vitro spontaneous contractions of right atria obtained from adult female rats of the Wistar strain were recorded. The atria were exposed to BPS (10-6-10 mM) and its effects on atrial contractions were recorded in the form of cumulative-concentration response with and without administration of antagonists namely atropine, L-NAME, and methylene blue.

RESULTS

BPS decreased the rate as well as the force of atrial contractions. The changes produced in the rate and force of atrial contractions were not attributed to ethanol, which was used to prepare BPS solutions. The decrease in right atrial contractility produced by BPS was blocked by L-NAME; however, atropine and methylene blue were not able to antagonize the effects of BPS on atria.

CONCLUSIONS

The present study indicates the involvement of NO-dependent but cGMP independent pathway responsible for BPS-induced cardio-toxicity.

Lignocaine augments the in-vitro uterine contractions involving NO-guanylyl cyclase dependent mechanisms

AIMS

Lignocaine is used during intrapartum and postpartum period but there are conflicting reports regarding the effect of lignocaine on uterine contractility. Therefore, this study was undertaken to delineate the effect of lignocaine on uterine contractility and the underlying mechanisms.

MAIN METHODS

The in vitro contractions were recorded from the uterine segments obtained from adult rats (in estrous phase) and also from human myometrial tissue. Effect of lignocaine on spontaneous uterine contractions was recorded in the absence or presence of antagonists. Effect of sodium nitroprusside (SNP, NO donor) on uterine contractility was assessed. The NO₂^- was assayed (indicator of NO activity) from the supernatant after exposing the myometrial tissue to lignocaine in the absence or the presence of L-NAME or hemoglobin.

KEY FINDINGS

Lignocaine (100μM) increased the amplitude of uterine contractions by 75% with no alterations in frequency. Similar magnitude of increase was seen with human myometrial tissue also. The spontaneous activities were absent in Ca²⁺-free or in nifedipine (10μM) containing medium. Heparin (IP₃ blocker, 10IU/ml), but not the indomethacin (10μM) blocked the lignocaine-induced augmentation. L-NAME (NOS inhibitor, 10μM) or methylene blue (guanylyl cyclase inhibitor, 100μM) partially blocked the lignocaine-induced augmentation. SNP (30μM) increased the amplitude of spontaneous uterine contractions. Lignocaine increased the NO₂^- content (indicator of NO activity) of uterine tissue and the increase was blocked by L-NAME or hemoglobin.

SIGNIFICANCE

Present observations indicate that lignocaine augments the amplitude of uterine contractions via Ca²⁺-dependent mechanisms involving NO-G cyclase-dependent mechanisms.

Acute effects of sildenafil and dobutamine in the hypertrophic and failing right heart in vivo

Abstract The purpose of this study was to investigate whether acute intravenous administration of the phosphodiesterase type 5 (PDE-5) inhibitor sildenafil in a single clinically relevant dose improves the in vivo function of the hypertrophic and failing right ventricle (RV). Wistar rats ([Formula: see text]) were subjected to pulmonary trunk banding (PTB) causing RV hypertrophy and failure. Four weeks after surgery, they were randomized to receive an intravenous bolus dose of sildenafil (1 mg/kg; [Formula: see text]), vehicle ([Formula: see text]), or dobutamine (10 μg/kg; [Formula: see text]). Invasive RV pressures were recorded continuously, and transthoracic echocardiography was performed 1, 5, 15, 25, 35, 50, 70, and 90 minutes after injecting the bolus. Cardiac function was compared to baseline measurements to evaluate the in vivo effects of each specific treatment. The PTB procedure caused significant hypertrophy, cardiac fibrosis, and reduction in RV function evaluated by echocardiography (TAPSE) and invasive pressure measurements. Sildenafil did not improve the function of the hypertrophic failing right heart in vivo, measured by TAPSE, RV systolic pressure (RVsP), and dp/dtmax. Dobutamine improved RV function 1 minute after injection measured by TAPSE ([Formula: see text] vs. [Formula: see text] cm; [Formula: see text]), RVsP ([Formula: see text] vs. [Formula: see text] mmHg; [Formula: see text]), and dp/dtmax ([Formula: see text] vs. [Formula: see text] mmHg/s; [Formula: see text]). Acute administration of the PDE-5 inhibitor sildenafil in a single clinically relevant dose did not modulate the in vivo function of the hypertrophic failing right heart of the rat measured by echocardiography and invasive hemodynamics. In the same model, dobutamine acutely improved RV function.