Search results for "cyclic"
showing 10 items of 2439 documents
Response of soil phosphatase activities to contamination with two types of tar oil.
2018
Tar oil is a complex mixture of hydrocarbon compounds obtained from high-temperature distillation of coal tar. It has been used for over 100 years from now to protect wood and has been applied to wood products, primary utility poles, and railroad ties by pressure methods. Composition of the tar oil depends on the source and typically consists of 85% polycyclic aromatic hydrocarbons (PAHs), 10% phenolic compounds, and 5% heterocyclic compounds. In this research, we performed the laboratory experiment to compare two types of tar oil: C and GX-Plus, and their effects on P-cycling enzymes (phosphatases) in sandy loam and loamy sand. Tar oil was applied to soil samples at the following doses: 2,…
Inhibitory effect of nonviable preparations from human immunodeficiency virus 1 on inositol phospholipid metabolism
1989
Previously it was established [Pahwa, S., Pahwa, R., Saxinger, C., Gallo, R. C. & Good, R. A. (1985) Proc. Natl Acad. Sci. USA 82, 8198] that nonviable preparations of human immunodeficiency virus 1 (HIV-1) abolish the proliferative response of human lymphocytes to phytohemagglutinin A. Now we describe that this effect might be, at least partially, due to an impairment of the function of phospholipase C. It was found that addition of HIV-1 preparation to lymphocytes diminished the stimulation of phosphatidylinositol phosphorylation caused by phytohemagglutinin A. Moreover, this preparation completely abolished the phytohemagglutinin-A-stimulated release of inositol trisphosphate and prevent…
Influence of cyclization and acyl substitution on the inotropic effects of adenine nucleotides.
1973
This study was designed to further elucidate relevance and mechanism of the positive inotropic action of cyclic N6-2′-O-dibutyryl-AMP (DB-c-AMP). For this purpose the effects of cyclic N6-monobutyryl-AMP (N6-MB-c-AMP), noncyclic N6-2′-O-3′-O-tributyryl-5′-AMP (TB-AMP), c-AMP, adenosine and various adenine nucleotides (ATP, ADP, AMP) on myocardial contractile force (CF) were investigated and compared to that of DB-c-AMP. The experiments were performed on isolated, electrically driven (frequency 2 Hz) rat left auricles, i.e. on a preparation in which DB-c-AMP consistently produced positive inotropic effects. The following results were obtained: From the failure of non-cyclic TB-AMP to increas…
Response of isolated human ventricular myocardium to cyclic AMP and its dibutyryl derivative.
1974
The contractile responses to c-AMP and DB-c-AMP were studied in isolated electrically stimulated human papillary muscle strips. C-AMP (1×10−4 to 1×10−3 M) had no effect on contractile force in all of 6 human papillary muscle preparations studied. In contrast, DB-c-AMP (10−4 to 5×10−3 M) produced a concentration-dependent and reversible positive inotropic effect which was associated by a decrease in time to peak force and in relaxation time and which was not inhibited by 10−6 M propranolol. The possibility of a clinical applicability of DB-c-AMP is discussed.
Papaverine enhances the negative inotropic effect of acetylcholine in rat auricles
1978
The negative inotropic effect of acetylcholine in rat left auricles is enhanced in the presence of the phosphodiesterase inhibitor papaverine. This result favours the idea of a cyclic GMP-mediated action of acetylcholine in the heart.
Opposite effects of beta-adrenoceptor stimulation and 8-bromo-cyclic AMP on potassium efflux in mammalian heart muscle.
1980
beta-adrenoceptor stimulation by isoprenaline increases the potassium efflux in beating guinea-pig atria. This effect is not mimicked by 8-bromo-cyclic AMP, a cyclic AMP analogue which exerts a positive inotropic effect in this preparation.
cGMP-Dependent Protein Kinase I Mediates the Negative Inotropic Effect of cGMP in the Murine Myocardium
2002
To study the role of cGMP-dependent protein kinase I (cGKI) for cardiac contractility, force of contraction (F c ) was studied in electrically driven heart muscle from wild-type (WT) mice and from conventional and conditional cGKI knockout mice. Both 8-Br-cGMP and 8-pCPT-cGMP reduced Fc in cardiac muscle from juvenile WT but not from juvenile cGKI-null mutants. Similarly, the cGMP analogues reduced F c in forskolin-stimulated ventricular muscle from WT mice but not from cGKI-null mutants. In contrast, carbachol reduced F c in both groups of animals. 8-Br-cGMP reduced F c also in heart muscle from adult WT mice but not from adult cardiomyocyte-specific cGKI-knockout mice. These results demo…
The positive inotropic effect of phenylephrine in the presence of propranolol. Increase in time to peak force and in relaxation time without increase…
1978
The effects of phenylephrine on the shape of the contraction curve and on the cyclic adenosine 3',5'-monophosphate (c-AMP) content were studied in electrically driven (frequency 0.2 Hz) cat papillary muscles. All experiments were done in the presence of 1 micron propranolol in order to minimize interference from beta-adrenoceptors. 1. Phenylephrine increased the force of contraction in a concentration-dependent manner. Maximal effects (about 200% of control) occurred at 30 micron phenylephrine. 2. The positive inotropic effect (PIE) of phenylephrine was antagonized by phentolamine. Phentolamine, 5 micron, produced a parallel shift of the concentration-response curve for the PIE of phenyleph…
A negative inotropic effect of acetylcholine in the presence of several phosphodiesterase inhibitors.
1981
The phosphodiesterase inhibitors papaverine, theophylline and 3-isobutyl-1-methylxanthine (IBMX) reveal a negative inotropic effect of acetylcholine in cat ventricular heart muscle. This effect in unrelated to beta-adrenoceptor stimulation and possibly mediated by the accumulation of cyclic GMP.
Cyclic AMP and cyclic GMP may play opposing roles in influencing force of contraction in mammalian myocardium.
1976
CYCLIC AMP and cyclic GMP have been suggested to play opposing regulatory roles in several biological systems1. Supporting evidence for the yin yang hypothesis of opposing biological regulation has been obtained in sympathetic ganglia2,3 and pyramidal neurones in the rat cerebral cortex4. In the mammalian heart, the role of cyclic AMP in mediating the positive inotropic response to catecholamines was advanced by the observation that the inotropic effect was preceded by an increase in cyclic AMP levels5. On the other hand, the levels of cyclic GMP were found to be increased after cholinergic stimulation6. In frog, oscillations of cyclic AMP7 and cyclic changes in the levels of cyclic AMP and…