Neurogenic peptides and the cardiomyopathy of magnesium-deficiency: Effects of substance P-receptor inhibition

Dietary deficiency of magnesium (Mg) in rodents results in cardiomyopathic lesion formation. In our rat model, these lesions develop after 3 weeks on the Mg-deficient diet; significant elevation of several cytokines, IL-1, IL-6 and TNF also occurs. In probing the mechanisms of lesion formation, we obtained data supporting the participation of free radicals (Freedman AMet al.: Bioch Biophys Res Commun 1990; 170: 1102). Recently, we identified an early elevation of circulating substance P and proposed a role of neurogenic peptides during Mg-deficiency (Weglicki WB, Phillips TM: Am J Phys 1992; 262: R734). The present study was designed to evaluate the contribution of neurogenic peptides to the pathogenesis of Mg-deficiency. In the blood, substance-P and calcitonin gene related peptide (CGRP) are elevated during the first week on the diet. During the second week, circulating histamine, PGE₂ and TBAR-materials were elevated and red cell glutathione was reduced, all prior to the elevation of the inflammatory cytokines during the third week. When the rats were treated with the substance P-receptor blocker [CP-96,345], the levels of substance P and CGRP remained elevated; however, increases in histamine, PGE₂, TBAR-materials, and the decrease in red cell glutathione were inhibited; also, the development of cardiac lesions was inhibited significantly. These data support a central role for neurogenic peptides, especially substance P, in the development of cardiomyopathic lesions during Mg-deficiency.     

The Regional Distribution of N-Acetylaspartylglutamate (NAAG) and Peptidase Activity Against NAAG in the Rat Nervous System

Abstract: N -Acetylaspartylglutamate (NAAG), a prevalent peptide in the vertebrate nervous system, may be hydrolyzed by extracellular peptidase activity to produce glutamate and N -acetylaspartate. Hydrolysis can be viewed as both inactivating the peptide after synaptic release and increasing synaptic levels of ambient glutamate. To test the hypothesis that NAAG and the peptidase activity that hydrolyzes it coexist as a unique, two-stage system of chemical neurotransmission, 50 discrete regions of the rat CNS were microdissected for assay. In each microregion, the concentration of NAAG was determined by radioimmunoassay and the peptidase activity was assayed using tritiated peptide as substrate. The NAAG concentration ranged from 2.4 nmol/mg of soluble protein in median eminence to 64 in thoracic spinal cord. Peptidase activity against NAAG ranged from 54 pmol of glutamate produced per milligram of membrane protein per minute in median eminence to 148 in superior colliculus. A linear relationship was observed between NAAG peptidase and NAAG concentration in 46 of the 50 areas, with a slope of 2.26 and a correlation coefficient of 0.45. These data support the hypothesis that hydrolysis of NAAG to glutamate and N -acetylaspartate is a consistent aspect of the physiology and metabolism of this peptide after synaptic release. The ratio of peptide concentration to peptidase activity was >0.3 in the following four areas: ventrolateral medulla and reticular formation where the peptide is concentrated in axons of passage, thoracic spinal cord, where NAAG is concentrated in ascending sensory tracts as well as motoneuron cell bodies, and ventroposterior thalamic nucleus.     

Interaction of mithramycin with isolated GC and CG sites

We have studied the interaction of the GC-specific, minor groove-binding ligand, mithramycin, with cloned DNA inserts containing isolated GC and CG sites flanked by regions of (AT)_n and A_n · T_n using DNase I and hydroxyl radical footprinting. We find that mithramycin binds to GC better than CG and that AGCT is a better site than TGCA. Sites flanked by (AT)_n appear to be bound better than those surrounded by A_n · T_n. Although no footprints are produced at T₉GCA₉ and T₁₅CGA₁₅, DNase I cleavage is enhanced with the GC sites suggesting that there is some interaction with the ligand. Mithramycin also alters the DNase I cleavage of (GA)_n · (CT)_n.     

Determination of trimethoprim in bovine serum by high-performance liquid chromatography with confirmation by thermospray liquid chromatography—mass spectrometry

A high-performance liquid chromatographic (HPLC) method with a detection limit of 5 ng/ml was developed for the analysis of trimethoprim in bovine serum. Trimethoprim and the internal standard, ormetoprim, under alkaline conditions, were first extracted into dichloromethane and then back-extracted into dilute sulphuric acid (0.15 M) and cleaned-up on a C₁₈ cartridge. Trimethoprim was quantified on a C₁₈ column using a triethylammonium acetate—acetonitrile—methanol (16:3:1, v/v/v) mobile phase at a flow-rate of 1.5 ml/min, with ultraviolet detection at 225 nm. This method was used to verify the accuracy of test responses obtained with the Brilliant Black Reduction test, a rapid screening method, for trimethoprim levels in the serum of steers treated with Trivetrin. Confirmation of the presence of trimethoprim in the sample extract was obtained by thermospray HPLC—mass spectrometry.     

Genotype and phenotype associations with drought tolerance in barley tested in North Africa

A review is presented of genetic strategies deployed in a 3-yr project on drought tolerance in barley. Data were collected on genetic, physiological and agronomic traits in non-irrigated and irrigated field trials in Egypt, Morocco and Tunisia. A wide range of barley germplasm (developed from African and European cultivars, adapted landraces and wild barleys) was tested, and positive traits were found in each gene pool. The contrasting environments of the three North African countries had major effects on plant/genotype performance. Genetic effects were also detected, as were genotype × environment interactions. A range of strategies were deployed to investigate the physiology and genetics of quantitative traits associated with field performance. Quantitative trait locus (QTL) analysis was performed using backcross lines, recombinant inbred lines and doubled haploid mapping populations. A detailed genetic map was generated in the Tadmor × (ER/Apm) recombinant inbred lines, an important mapping population specifically developed by ICARDA (Centre for Agricultural Research in Dry Areas) and CIMMYT (International Maize and Wheat Improvement Center) to study drought. Quantitative trait loci (QTLs) for grain yield and other important morphological and physiological traits were also identified in a population of doubled haploids derived from F2BCj plants from a cross between a cultivar and a wild barley accession. Significantly, the wild parental line was found to contribute a number of positive alleles for yield. Effects of major developmental genes could explain many of the responses observed. QTLs were found to cluster around major genes controlling flowering time (sghI), plant stature (sdwI and arie.GP) and ear type (vrsl), and it is highly likely that the associations represent pleiotropic effects. Some QTLs were associated with candidate genes such as dehydrins and rubisco activase. One of the most significant results was the identification and generation of material that out performed the best local standards in the three participating North African countries; the selected lines have now entered local breeding programmes. The strategies adopted provided information on physiological traits, genotypes and genetic markers that could be used for marker-assisted selection. Target QTLs and their associated genetic markers may be deployed in marker assisted selection programmes to match crop phenology to the field environment.     

Modifications of anionic-lipid domains preceding membrane fusion in guinea pig sperm

The relationship between anionic-lipid concentration and the functional properties of plasma-membrane domains was explored using the guinea-pig sperm membrane as a model, with polymyxin B (PXB) as a probe. Areas of plasmalemma specialized for fusion during the acrosome reaction had a higher affinity for the probe than adjacent nonfusigenic regions. In addition, capacitation--a process preceding acrosome:plasma-membrane fusion--markedly enlarged the area susceptible to PXB binding over the acrosomal cap. Protease treatment mimicked capacitation by increasing the acrosome-reaction incidence as well as PXB binding, at enzyme concentrations not affecting the surface coat nor altering filipin/sterol localization. Both proteolytic digestion and capacitation failed to augment PXB- or filipin-affinity in nonfusigenic zones, such as the post-acrosomal segment, including its particle-free maculae. Incubation of sperm in capacitating medium supplemented with 32P-labeled phosphate, followed by lipid extraction, thin-layer chromatography, and autoradiography, revealed a radioactive band comigrating with cardiolipin and phosphatidic acid. Vermiform protrusions elicited by PXB in the outer lamellae of cardiolipin- phosphatidylcholine liposomes resembled those seen in fusional regions of sperm membrane. We conclude that (a) differing concentrations of anionic lipids are found in adjacent domains of the sperm plasma membrane; (b) these domains mirror the functional regions of the membrane, with higher anionic-lipid concentrations localized over fusional zones; (c) the surface coat does not participate in the maintenance of such domains; (d) anionic-lipid synthesis may contribute to their formation; and (e) anionic-lipid concentrations increase as the membrane becomes fusionally competent, indicating that cellular modulation of lipid domains accompanies regulation of membrane function.