Rosiglitazone treatment restores renal responsiveness to atrial natriuretic peptide in rats with congestive heart failure

The thiazolidinedione (TZD) class of Peroxisome proliferator‐activated receptor gamma agonists has restricted clinical use for diabetes mellitus due to fluid retention and potential cardiovascular risks. These side effects are attributed in part to direct salt‐retaining effect of TZDs at the renal collecting duct. A recent study from our group revealed that prolonged rosiglitazone (RGZ) treatment caused no Na+/H₂O retention or up‐regulation of Na⁺ transport‐linked channels/transporters in experimental congestive heart failure (CHF) induced by surgical aorto‐caval fistula (ACF). The present study examines the effects of RGZ on renal and cardiac responses to atrial natriuretic peptide (ANP), Acetylcholine (Ach) and S‐Nitroso‐N‐acetylpenicillamine (SNAP‐NO donor). Furthermore, we assessed the impact of RGZ on gene expression related to the ANP signalling pathway in animals with ACF. Rats subjected to ACF (or sham) were treated with either RGZ (30 mg/kg/day) or vehicle for 4 weeks. Cardiac chambers pressures and volumes were assessed invasively via Miller catheter. Kidney excretory and renal hemodynamic in response to ANP, Ach and SNAP were examined. Renal clearance along with cyclic guanosine monophosphate (cGMP), gene expression of renal CHF‐related genes and ANP signalling in the kidney were determined. RGZ‐treated CHF rats exhibited significant improvement in the natriuretic responses to ANP infusion. This ‘sensitization’ to ANP was not associated with increases in neither urinary cGMP nor in vitro cGMP production. However, RGZ caused down‐regulation of several genes in the renal cortex (Ace, Nos3 and Npr1) and up‐regulation of ACE2, Agtrla, Mme and Cftr along down‐regulation of Avpr2, Npr1,2, Nos3 and Pde3 in the medulla. In conclusion, CHF+RGZ rats exhibited significant enhancement in the natriuretic responses to ANP infusion, which are known to be blunted in CHF. This ‘sensitization’ to ANP is independent of cGMP signalling, yet may involve post‐cGMP signalling target genes such as ACE2, CFTR and V2 receptor. The possibility that TZD treatment in uncomplicated CHF may be less detrimental than thought before deserves additional investigations.     

Increased Instability of Human CTG Repeat Tracts on Yeast Artificial Chromosomes during Gametogenesis

Expansion of trinucleotide repeat tracts has been shown to be associated with numerous human diseases. The mechanism and timing of the expansion events are poorly understood, however. We show that CTG repeats, associated with the human DMPK gene and implanted in two homologous yeast artificial chromosomes (YACs), are very unstable. The instability is 6 to 10 times more pronounced in meiosis than during mitotic division. The influence of meiosis on instability is 4.4 times greater when the second YAC with a repeat tract is not present. Most of the changes we observed in trinucleotide repeat tracts are large contractions of 21 to 50 repeats. The orientation of the insert with the repeats has no effect on the frequency and distribution of the contractions. In our experiments, expansions were found almost exclusively during gametogenesis. Genetic analysis of segregating markers among meiotic progeny excluded unequal crossover as the mechanism for instability. These unique patterns have novel implications for possible mechanisms of repeat instability.     

The role of cyanobacterial exopolysaccharides in structuring desert microbial crusts

Abstract: Microbial crusts are present on surfaces of soils throughout the world. A key feature of these crusts in arid zones is the abundance of filamentous sheath-forming and polysaccharide-excreting cyanobacteria. Several isolates of cyanobacteria were prepared from crust samples (Nizzana sand dunes, north-western Negev Desert, Israel). Optimal growth conditions for two such isolates of Microcoleus sp. were defined, and the role of the excreted polysaccharides in affecting the hydrological properties of crust-covered sand dunes was studied. Experiments with the native crust microbial population demonstrated the possibility of net primary productivity at both high relative air humidities and low moisture content.     

Prolonged Expression of Interferon-Inducible Protein-10 in Ischemic Cortex After Permanent Occlusion of the Middle Cerebral Artery in Rat

Abstract: Focal cerebral ischemia elicits local inflammatory reaction as demonstrated by the accumulation of inflammatory cells and mediators in the ischemic brain. Interferon-inducible protein-10 (IP-10) is a member of the C-X-C chemokine family that possesses potent chemoattractant actions for monocytes, T cells, and smooth muscle cells. To investigate a potential role of IP-10 in focal stroke, we studied the temporal expression of IP-10 mRNA after occlusion of the middle cerebral artery in rat by means of northern analysis. IP-10 mRNA expression after focal stroke demonstrated a unique biphasic profile, with a marked increase early at 3 h (4.9-fold over control; p < 0.01), a peak level at 6 h (14.5-fold; p < 0.001) after occlusion of the middle cerebral artery, and a second wave induction 10–15 days after ischemic injury (7.2- and 9.3-fold increase for 10 and 15 days, respectively; p < 0.001). In situ hybridization confirmed the induced expression of IP-10 mRNA and revealed its spatial distribution after focal stroke. Immunohistochemical studies demonstrated the expression of IP-10 peptide in neurons (3–12 h) and astroglial cells (6 h to 15 days) of the ischemic zone. To explore further the potential role of IP-10 in focal stroke, we demonstrated a dose-dependent chemotactic action of IP-10 on C6 glial cells and enhanced attachment of rat cerebellar granule neurons. Taken together, the data suggest that ischemia induces IP-10, which may play a pleiotropic role in prolonged leukocyte recruitment, astrocyte migration/activation, and neuron attachment/sprouting after focal stroke.     

TRH: Cardiovascular and sympathetic modulation in brain nuclei of the rat

The cardiovascular and sympathetic effects of TRH in discrete cardiovascular-related brain nuclei were studied. Microinjections of TRH were made into the nucleus preopticus medialis (POM) of conscious rats and the nucleus tractus solitarius (NTS) of pentobarbitone-anesthetized, artificially respired rats. POM injections (1 μl, 0.8–80 nM) elicited dose dependent pressor and tachycardic responses which were accompanied by increased levels of norepinephrine (NE) and epinephrine (EPI) in the plasma. These pressor/tachycardic effects of TRH were also elicited in adrenal demedullated (ADM-x) rats, but completely abolished in ADM-x rats pretreated with bretylium (30 mg/kg, IA). NTS injections (0.1 μl, 30 and 150 nM) had a short depressor effect on blood pressure (BP) and a delayed increase in heart rate (HR). From these findings we suggest that the POM, a central nucleus in the AV3V region, may be an important forebrain site for autonomic regulation by TRH, mediated through the sympathetic nervous system.     

II. Validity and reliability of liquid chromatography with electrochemical detection for measuring plasma levels of norepinephrine and epinephrine in man

Liquid chromatography with electrochemical detection (LCEC) provides a rapid, sensitive, and specific technique for measuring human plasma norepinephrine (NE) and epinephrine (E) levels. We tested the reliability and validity of this technique against that of the catechol-O-methyl-transferase radioenzymatic (COMT-RE) assay. In healthy, resting humans, mean NE and E values were similar using the LCEC and COMT-RE techniques (311 vs. 300 pg/ml for NE; 57 vs. 52 pg/ml for E). In a series of 25 plasma samples obtained from a variety of sources, the correlation between the two methods was 0.99 for both NE and E. Coefficients of variation were similar for catecholamine levels above 100 pg/ml, but below this, the COMT-RE technique appeared to be more reliable. The advantages of the LCEC method are its speed, simplicity of sample preparation, low cost per assay, lack of use of radionuclides, and ease in trouble-shooting. The COMT-RE technique is preferable for small sample sizes or large numbers of samples. LCEC offers a reasonable alternative to the COMT-RE technique for measuring plasma norepineprhine and epinephrine.     

Sensitivity of meiotic yeast cells to ultraviolet light

Sporulating cells of Saccharomyces cerevisiae show an increasing sensitivity to ultraviolet irradiation. Maximum sensitivity is reached at a time comparable to meiotic prophase. Sensitivity is expressed as reduced sporulation after the irradiation. The uv effect can be efficiently reversed by photoreactivating light. Viability is also more severely affected during premeiotic DNA synthesis and during meiosis than in earlier stages in sporulation. Cells left in sporulation medium after the irradiation show a reduced viability compared with the cells plated immediately after the irradiation. Non-sporulating diploids do not acquire sensitivity when exposed to sporulation medium, hence the sensitivity is related to the sporulation process. That meiosis itself is affected, rather than spore formation alone, is evident from experiments in which the uv irradiation interferes with the uncovering of a recessive marker and with commitment to meiosis. It is proposed that during meiotic prophase, the DNA repair system is different from that found in vegetative cells.     

DNA degradation and reduced recombination following UV irradiation during meiosis in yeast (Saccharomyces cerevisiae)

Summary Irradiation of meiotic yeast cells with moderate doses of ultraviolet irradiation (1,600 erg/mm²) leads to the arrest of premeiotic DNA synthesis, massive (5–40%) DNA degradation, and a 40–50% loss of cell viability. In contrast, such doses of UV irradiation had a minor effect on viability (15–20% loss) of logarithmically growing cells, and no comparable DNA degradation was observed in irradiated synchronized vegetative cells. Meiotic recombination is also affected by UV irradiation. When administered at a stage comparable to meiotic prophase, low doses of irradiation result in a reduction in recombination frequency without significantly affecting cell viability.