NG-nitro-L-arginine methyl ester potentiates the effect of aminophylline on the isolated rat hemidiaphragm

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.

[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.

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

The role of extracellular calcium in the interaction between intracellular cAMP and nitric oxide (NO)/cGMP on the contractility of rat diaphragm pretreated with cumulative concentrations of aminophylline (0.36 - 3.60 mM) was investigated. In a Ca2+-free medium, NG-nitro-L-arginine methyl ester (L-NAME) (1 and 3 mM) depressed tension developed (Td) and also aminophylline-induced potentiation of Td in a concentration-dependent manner. Verapamil (2.5 microM) or nicardipine (20 microM) significantly antagonized the potentiating effect of L-NAME on Td in a calcium-containing medium. However, in the presence of verapamil or nicardipine, L-NAME still produced statistically significant potentiation of the cumulative concentrations of aminophylline (0.36 - 3.60 mM), given in the second series.