NG-Nitro-L-arginine Methyl Ester-Induced Potentiaton of the Effect of Aminophylline on Rat Diaphragm: the Role of Extracellular Calcium

The opposite effect of convulsant drugs on neuronal and endothelial nitric oxide synthase - A possible explanation for the dual proconvulsive/anticonvulsive action of nitric oxide

Nitric oxide (NO) participates in processes such as endothelium-dependent vasodilation and neurotransmission/neuromodulation. The role of NO in epilepsy is controversial, attributing it to anticonvulsant but also proconvulsant properties. Clarification of this dual effect of NO might lead to the development of new antiepileptic drugs. Previous results in our laboratory indicated that this contradictory role of NO in seizures could depend on the nitric oxide synthase (NOS) isoform involved, which could play opposite roles in epileptogenesis, one of them being proconvulsant but the other anticonvulsant. The effect of convulsant drugs on neuronal NO (nNO) and endothelial NO (eNO) levels was investigated. Considering the distribution of neuronal and endothelial NOS in neurons and astrocytes, resp., primary cultures of neurons and astrocytes were used as a study model. The effects of convulsant drugs pentylenetetrazole, thiosemicarbazide, 4-aminopyridine and bicuculline on NO levels were studied, using a spectrophotometric method. Their effects on NO levels in neurons and astrocytes depend on the concentration and time of treatment. These convulsant drugs caused an increase in nNO, but a decrease in eNO was proportional to the duration of treatment in both cases. Apparently, nNO possesses convulsant properties mediated by its effect on the glutamatergic and GABAergic systems, probably through GABA_A receptors. Anticonvulsant properties of eNO may be the consequence of its effect on endothelial vasodilation and its capability to induce angiogenesis. Described effects last as seizures do. Considering the limitations of these kinds of studies and the unexplored influence of inducible NO, further investigations are required.

Why is nitric oxide important for our brain?

The freely diffusible gaseous compound nitric oxide (NO) has been shown to be an important messenger in many organ systems throughout the body, and particularly in the central nervous system (CNS). The importance of NO as an intermediary in cell communication in the brain is highlighted by the fact that the excitatory amino acid glutamate, the most abundant CNS neurotransmitter, is an initiator of the reaction that forms NO. Because of its numerous physiological and pathophysiological roles, the impact of NO on clinical medicine is developing. NO can act as a "double-edged sword" and it has been demonstrated that clarification of the dual effect of NO might have implications for clinical medicine, and could lead to the emergence of therapeutic opportunities. Accordingly, NO was proclaimed "Mole cule of the Year" in 1992 by the journal Science, while discovery of the pathways and roles of NO was acknowledged with the Nobel Prize in 1998. Additionally, the ubiquity of NO in the CNS implies that drugs designed to modify the biological activity of NO may have distinct effects. Thus, further clinical applications of NO, of its analogs or of newly developed NOS inhibitors are forthcoming. The therapeutic challenge would be to succeed in manipulating the NO pathways selectively.

[Effects of new nitric oxide synthase inhibitors on spontaneous locomotor activity]

INTRODUCTION

New nitric oxide synthase (NOS) inhibitors: 3-bromo-7-nitroindazole (3-Br-7-NI), 1-(2-trifluoromethylphenyl) imidazole (TRIM), S-methyl-L-thiocitrulline (S-Me-TC) and 7-nitroindazole (7-NI) reduce spontaneous locomotor activity in mice.

MATERIAL AND METHODS

In order to elucidate central effects of NOS inhibitors on locomotor activity, the influence of 7-NI on electroencephalographic (EEG) power spectrum in rats was investigated.

RESULTS

7-NI reduced the EEG power density in all frequency bands in rats, suggesting a depression of the central neuronal activity. The electrophysiologic power was most reduced in the range of 7-9 Hz of the rhythmic slow activity (theta rhythm), which is in accordance with decreased locomotor activity observed following administration of NOS inhibitors.

CONCLUSION

The present results indicate that nitric oxide exerts an excitatory effect on central neuronal structures involved in regulation of locomotion.

A selective beta2-adrenergic agonist, terbutaline, improves sepsis-induced diaphragmatic dysfunction in the rat

BACKGROUND

Sepsis causes diaphragmatic dysfunction, which can lead to the development of respiratory failure. We previously reported that isoproterenol, non-selective beta-adrenergic agonist, improved contractility of the diaphragm in a septic rat model. Since beta(2)-adrenoceptor agonists are widely used in the treatment of chronic respiratory disease, we investigated the effect of terbutaline, a selective beta(2)-adrenergic agonist, on contractility of the septic rat diaphragm and the contribution of intracellular Ca(2+) to the effect of terbutaline in vitro.

METHODS

Forty-eight rats were divided into a sham group (in which sham laparotomy was performed) and a CLP group (in which peritonitis was induced by cecal ligation and perforation). The left hemidiaphragm was removed at 16 h after the operation. The effect of terbutaline (10(-)(6) M) on contractility of the diaphragm was assessed by twitch characteristics (twitch tension, contraction time and contraction velocity) and force-frequency relationship. In addition, to investigate the role of calcium ions in the effect of terbutaline on contractility of the diaphragm, contractility of the diaphragm was assessed after the pre-incubation of the diaphragm with methoxy-verapamil (10(-)(5) M), Ca(2+)-free Krebs-Ringer's solution buffered with 2 mM of ethylene glycol tetra-acetic acid (EGTA), and ryanodine (10(-)(6) M).

RESULTS

Terbutaline significantly improved twitch characteristics and force-frequency relationship of the diaphragm in the CLP group (P<0.01). Incubation with methoxy-verapamil or calcium-free solution with EGTA did not show any changes in the inotropic effect of terbutaline in the CLP group. However, incubation with ryanodine completely abolished the inotropic effect of terbutaline in the CLP group.

CONCLUSIONS

The present study demonstrated that terbutaline increased contractility of the diaphragm in the septic rats. Since this inotropic effect was abolished by ryanodine administration, calcium release from the sarcoplasmic reticulum may contribute to the terbutaline-induced improvement in dysfunction of the septic diaphragm.

[Nitric oxide, neurodegeneration, and Parkinson's disease]

<zakljucak> Brojni rezultati velikih studija pokazuju znacajnu ulogu NO u kaskadi dogadjaja koji dovode do smrti dopaminergickih neurona. Zna se da MPTP uzrokuje neurotoksicnost putem NO sintetisanog pomocu nNOS, ostecujuci primarno dopaminergicka vlakna i zavrsetke u strijatumu, dok NO stvoren uz pomoc iNOS deluje prvenstveno na tela dopaminergickih neurona u pars compacta substantia nigra. Ostecenje uzrokovano NO iz nNOS moze sluziti kao katalizator aktivacije iNOS i glioze. Slican sled dogadjaja moze se primeniti na ostecenje dopaminergickih neurona kod ljudi, bilo usled idiopatske PB ili usled intoksikacije MPTP. Znacaj ovih otkrica je ne samo u osvetljavanju cinioca koji ucestvuju u progresiji neurodegeneracije i PB vec i u upucivanju na nove terapijske mogucnosti.

Type of Electrical Stimulation Influences Diaphragm Response to Adrenoceptor and Calcium Channel Modulators: the Role of Extracellular and Intracellular Calcium Events

The influence of direct single pulse and subtetanic electrical stimulation (ES) on isolated rat hemidiaphragm response to adrenoceptor antagonists and calcium channel blockers was investigated. Muscle contractility was stimulated by cumulative micromolar noradrenaline. Noradrenaline effects on developed tension (Td) in the presence of various alpha- and beta-adrenoceptor antagonists (e.g., prazosin and ICI 118551) were qualitatively different during different types of ES. Also, intact L-voltage calcium channels were necessary for noradrenaline-induced potentiation of Td during both types of ES, while the balance between ryanodine receptors- and inositol triphosphate (IP3)-related calcium events in the muscle was influenced by the pattern of the ES.

Aminophylline Pretreatment Modulates the Nitric Oxide System of the Isolated Rat Diaphragm: the Role of Frequency of the Electrical Stimulation

The effect of different frequencies of direct subtetanic electrical stimulation (14, 20, and 30 Hz) and aminophylline (AMPh) pretreatment on the effect of N(G)-nitro-L-arginine methyl ester (L-NAME) (1 mM) on isolated rat diaphragm was investigated. L-NAME potentiated tension developed (Td) in the diaphragm pretreated with a single concentration of AMPh (1.08 mM) in a frequency-dependent manner. The effect was significantly different in comparison with muscle incubated 30 min with Tyrode solution only. In the muscle pretreated with cumulative concentrations of AMPh (0.36 - 3.60 mM), the frequency-dependent potentiation of Td induced by L-NAME and the difference between L-NAME-treated and untreated muscle were lost.