Studies on the mode of action of hydrallazine and reserpine

Hydrallazine and reserpine are used in the treatment of hypertension and reserpine is also employed in the treatment of certain forms of mental illness. Hypotheses regarding the mode of action of these drugs are numerous. Thus hydrallazine is believed to act on the vasometer centre and reserpine to depress central sympathetic tone. Reserpine is also believed to mediate its actions by liberating noradrenaline and 5-hydroxytryptamine from the brain and, in the case of noradrenaline, from the arteries. The work described in this thesis, undertaken to clarify some aspects of the mode: of action of these drugs at cellular level. Experimental evidence has indicated that hydrallazine, dihydrallazine and related compounds did not antagonise certain pressor reflexes - notably the pressor responses due to central vagal stimulation, bilateral carotid occlusion and anoxia. This speaks against their having a central site and mechanism of action, because if this were so, all pressure refluxes mediated via the central nervous system should, he antagonised or depressed. This does not, however rule out the possibility that hydrallazine acts specifically upon certain cell groups in the central nervous system. Hydrallazine antagonised the pressor effect of adrenaline more than those of noradrenaline, and the antagonism of this drug to some pressor reflexes only was explained by assuming that there are quantitative variations in the proportions of the two humoral agents secreted during the initiation of these reflexes. The fact that hypertension caused by constant infusion of a solution of adrenaline was promptly brought back to normal levels by hydrallazine, also favours a peripheral site of action for this drug. Many of the effects of hydrallazine and reserpine can be explained by assuming that both drugs interfere with the normal energy-yielding mechanisms of the smooth muscle cell. It has been shown that hydrallazine has an effect upon carbohydrate metabolism which underlies its actions upon isolated arterial smooth muscle. Intermediate a of carbohydrate metabolism antagonised hydrallazine depression of drug-induced contractions of arterial smooth muscle. The reserpine effect was so persistent that the tissue did not recover. Anoxia and cyanide also antagonised drug-induced contractions of arterial smooth muscle. Intermediates of carbohydrate metabolism gave protection against anoxia and not against cyanide. The use of hydrallazine was, in effect analogous to rendering the tissue anoxic. Reserpine did not have marked effects on tissue respiration while hydrallazine depressed it. Reserpine was found to cause in vivo inhibition of oxidative phosphorylation in rat brain and livery since the ATP/ADP ratio was significantly lowered. Hydrallazine had similar effects in rat brain and liver. Neither drug influenced the, adenosine nucleotide levels in rat skeletal muscle and heart. On the basis of this experimental evidence it has been suggested that hydrallazine may interfere with biological oxidation and reserpine with oxidative phosphorylation. It has been shown that reserpine depleted the adrenal medulla of catechol amines and ATP in roughly the same proportions. Since the characteristic breakdown products of ATP (ADP and AMP) were not found as they were: found in brain and liver it is suggested that ATP possesses a specialised function in the storage or release of catechol amines from this gland. 4. Inhibitors of metabolism, such as cyanide and have marked effects on the transport of sodium and potassium ions in tissues. Roserpine was found to have practically no effect either upon the release of potassium or on the uptake of potassium and sodium. Hydrallazine, however, increased the release of potassium. It decreased potassium retention but increased sodium retention. Cyanide and aside increased potassium release but anoxia and IMP had no effect. On the other hand, cyanide, aside, Die and anoxia had marked effects on sodium and potassium uptakes Which usually , varied inversely. Thus a reduction in the efficiency of the enzymes controlling metabolism may reduce the ability of muscle to retain potassium, resulting in the release of this ion. Hydrallazine formed chelates with different metals, and the iron-hydrallazine chelate was shown to be inert. Hydrallazine in high doses inhibited catalase, depressed the iron-catalysed oxidation of cysteine to cystine and was shown to cause haemolysis. Doses of reserpine and hydrallazine used in this study are (moldered by the author to be comparable to those used in man. Since the intact experimental animal or man is more sensitive than the isolated tissue or organ, the slightly higher doses used in some experiments on isolated tissues do in fact approximate to the therapeutic dose levels. It is finally suggested that interference by these drugs with tissue metabolism may result in a decreased availability of energy for muscular contraction. It is postulated that hydrallazine Produces an "anoxia-like" condition in smooth muscle, while in oxidative phosphorylation, reserpine acts as an "uncoupling agent". Such an effect may explain the reduction of inherent tone in vascular smooth muscle and is probably responsible for the lowering of blood pressure

The tylosin resistance gene tlrB of Streptomyces fradiae encodes a methyltransferase that targets G748 in 23S rRNA

Metals in Catalysis, Biomimetics & Inorganic Material

Relativistic effects on the nuclear magnetic shielding tensor

A new approach for calculating relativistic corrections to the nuclear magnetic shieldings is presented. Starting from a full relativistic second order perturbation theory expression a two-component formalism is constructed by transforming matrix elements using the elimination of small component scheme and separating out the contributions from the no-virtual pair and the virtual pair part of the second order corrections to the energy. In this way we avoid a strong simplification used previously in the literature. We arrive at final expressions for the relativistic corrections which are equivalent to those of Fukui et al. J. Chem Phys. 105, 3175 (1996) and at some other additional terms correcting both the paramagnetic and the diamagnetic part of the nuclear magnetic shielding. Results for some relativistic corrections to the shieldings of the heavy and light nuclei in HX and CHȝX (X=Br,I) at both random phase and second order polarization propagator approach levels are given.Fil: Melo, Juan Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Ruiz de Azua, Martín César. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Giribet, Claudia Gloria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Aucar, Gustavo Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura. Departamento de Física; ArgentinaFil: Romero, Rodolfo Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura. Departamento de Física; Argentin

Rational Design of a New Trypanosoma rangeli Trans-Sialidase for Efficient Sialylation of Glycans

This paper reports rational engineering of Trypanosoma rangeli sialidase to develop an effective enzyme for a potentially important type of reactivity: production of sialylated prebiotic glycans. The Trypanosoma cruzi trans-sialidase and the homologous T. rangeli sialidase has previously been used to investigate the structural requirements for trans-sialidase activity. We observed that the T. cruzi trans-sialidase has a seven-amino-acid motif (197-203) at the border of the substrate binding cleft. The motif differs substantially in chemical properties and substitution probability from the homologous sialidase, and we hypothesised that this motif is important for trans-sialidase activity. The 197-203 motif is strongly positively charged with a marked change in hydrogen bond donor capacity as compared to the sialidase. To investigate the role of this motif, we expressed and characterised a T. rangeli sialidase mutant, Tr13. Conditions for efficient trans-sialylation were determined, and Tr13's acceptor specificity demonstrated promiscuity with respect to the acceptor molecule enabling sialylation of glycans containing terminal galactose and glucose and even monomers of glucose and fucose. Sialic acid is important in association with human milk oligosaccharides, and Tr13 was shown to sialylate a number of established and potential prebiotics. Initial evaluation of prebiotic potential using pure cultures demonstrated, albeit not selectively, growth of Bifidobacteria. Since the 197-203 motif stands out in the native trans-sialidase, is markedly different from the wild-type sialidase compared to previous mutants, and is shown here to confer efficient and broad trans-sialidase activity, we suggest that this motif can serve as a framework for future optimization of trans-sialylation towards prebiotic production

Therapeutic approach to FSGS in children

Therapy of primary focal segmental glomerulosclerosis (FSGS) in children incorporates conservative management and immunosuppression regimens to control proteinuria and preserve kidney function. In long-term cohort studies in adults and children with primary FSGS, renal survival has been directly associated with degree of proteinuria control. This educational article reviews the current therapeutic approach toward children with primary FSGS