Cardiac dysrhythmia produced by Mesobuthus tamulus venom involves NO-dependent G-Cyclase signaling pathway

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.

Mesobuthus tamulus venom induces acute respiratory distress syndrome in rats involving additional mechanisms as compared to oleic acid model

The present study was undertaken to determine whether acute respiratory distress syndrome (ARDS) is produced after Mesobuthus tamulus (MBT) envenomation and compared it with oleic acid (OA)-induced ARDS. The trachea, jugular vein and femoral artery were cannulated in anesthetized adult rats. Lethal dose of MBT venom (5 mg/kg) or OA (75 μL) was administered intravenously and the time-dependent changes in respiratory frequency (RF), heart rate (HR) and mean arterial pressure (MAP) were recorded. Minute ventilation (MV) and the PaO2/FiO2 (P/F) ratio were also determined. At the end lungs were excised, one lung was used for histopathological examination and the other was used for determination of pulmonary water content physically. MBT venom or OA produced hypoxemia, pulmonary pathology (alveolar damage, infiltration of inflammatory cells, capillary damage and exudation) and pulmonary edema implicating for ARDS. However, the hypoxemia in MBT venom group was associated with decreased MV, apnea/bradypnea, and bradycardia whereas, in OA group it was seen with increased MV, tachypnea, and tachycardia. Lack of effect of hypoxemic drive on RF/MV or HR in MBT venom group unlike OA group, suggests the involvement of medullary centers. The present results demonstrate that MBT venom produces ARDS. However MBT venom-induced ARDS involves pulmonary as well as extrapulmonary mechanisms.

The effect of bisphenol A on some oxidative stress parameters and acetylcholinesterase activity in the heart of male albino rats

Bisphenol A (BPA) is an endocrine disrupting chemical used on a wide range in industry. Several studies reported that BPA may cause cardiovascular disorders in humans and animals. The present study aims to investigate the effect of BPA on the heart of adult male rats. The rats received a daily oral administration of BPA (25 mg/kg for 6 weeks and 10 mg/kg for 6 and 10 weeks). It was found that BPA at the two studied doses induced a significant increase in malondialdehyde, and a significant decrease in catalase after 6 weeks. Moreover, a significant decrease in reduced glutathione and acetylcholinesterase (AchE) activity was observed after treatment with the two doses of BPA throughout the studied time intervals. The two doses (25 and 10 mg/kg) resulted in a significant decrease in nitric oxide (NO) levels after 6 and 10 weeks, respectively. A significant increase in body weight gain occurred in all animals after BPA treatment. These results suggest that BPA has cardiotoxic effects which are mediated by the oxidative stress resulting from the overproduction of free radicals, the deficiency of NO and the inhibition of AchE leading to cholinergic activation. The obesity promoting effect of BPA may also participate in the observed cardiovascular disturbances.