Homologous and heterologous desensitization of guanylyl cyclase-B signaling in GH3 somatolactotropes

The guanylyl cyclases, GC-A and GC-B, are selective receptors for atrial and C-type natriuretic peptides (ANP and CNP, respectively). In the anterior pituitary, CNP and GC-B are major regulators of cGMP production in gonadotropes and yet mouse models of disrupted CNP and GC-B indicate a potential role in growth hormone secretion. In the current study, we investigate the molecular and pharmacological properties of the CNP/GC-B system in somatotrope lineage cells. Primary rat pituitary and GH3 somatolactotropes expressed functional GC-A and GC-B receptors that had similar EC50 properties in terms of cGMP production. Interestingly, GC-B signaling underwent rapid homologous desensitization in a protein phosphatase 2A (PP2A)-dependent manner. Chronic exposure to either CNP or ANP caused a significant down-regulation of both GC-A- and GC-B-dependent cGMP accumulation in a ligand-specific manner. However, this down-regulation was not accompanied by alterations in the sub-cellular localization of these receptors. Heterologous desensitization of GC-B signaling occurred in GH3 cells following exposure to either sphingosine-1-phosphate or thyrotrophin-releasing hormone (TRH). This heterologous desensitization was protein kinase C (PKC)-dependent, as pre-treatment with GF109203X prevented the effect of TRH on CNP/GC-B signaling. Collectively, these data indicate common and distinct properties of particulate guanylyl cyclase receptors in somatotropes and reveal that independent mechanisms of homologous and heterologous desensitization occur involving either PP2A or PKC. Guanylyl cyclase receptors thus represent potential novel therapeutic targets for treating growth-hormone-associated disorders

Characterization of acid tar waste from benzol purification

The use of concentrated sulphuric acid to purify benzene, toluene and xylene produces acidic waste known as acid tar. The characterization of the acid tar to determine the composition and physical properties to device a way to use the waste was done. There were three acid tars two from benzene (B acid tar), toluene and xylene (TX acid tar) purification streams and one which was from the storage tank (HT acid tar). The viscosity and density varied greatly amoung the three acid tars with B acid tar having the lowest viscosity (28.3mPa.s) and HT acid tar having the highest viscosity (63.592Pa.s). For density HT had the lowest (1.43g/ml) and TX had the highest (1.549g/ml). The sulphuric acid % concentration was 15.4% for HT, 23.7% for TX and 24.2% for B acid tar. The solubility test also showed a difference in the three acid tars, B acid tar was more soluble in water than in methanol while the other two were more soluble in methanol than in water. GC MS and FT-IR results showed that TX and HT acid tars had weak organic acid such carboxylic acid, alcohols and aldehydes. The B acid tar had few organics as compared to TX and HT. The results show that the sulphuric acid is being lost in the holding tank and the physical and chemical properties of B and TX acid tar are different thus the need to treat differently if they are to be treated separately. The HT acid tar has properties that make it easier to work with; an example is the high viscosity and the high organic content.Keywords: Acid tar, benzol processing, sulphuric acid, organic acids, characterization and viscosit

Physical and chemical characterization of acid tar waste from crude benzol refining

The physical and chemical composition of acid tar waste is important in assessing and developing technological processing options for their subsequent utilization. In the present investigation gas chromatography/mass spectrometry (GC/MS), fourier transform infrared (FTIR), inductively coupled plasma/atomic emission spectrometry (ICP/AES), scanning electron microscopy with energy dispersive Xray (SEM/EDX) were mainly used to characterize the acid tar waste from crude benzol refining. The acid tar waste had a moisture content within the range 7-11%, pH values < 2.5 at a Liquid Solid (L/S) ratio of 20. Chemical analysis indicated the presence calcium, phosphorus and iron at 56.3, 15.7 and 11.3 ppm respectively with trace concentrations of lead, zinc, manganese and chromium. Organic analysis of the aromatic fraction of the acid tar waste by GC-MS revealed a wide range of compounds, including polycyclic aromatic hydrocarbons, furans, phenols, thiophenes and biphenyls. FTIR analysis was used to complement GC-MS. These results may be useful in the design and development of technological processes that can utilize acid tar waste.Keywords: Acid tars; Analytical techniques; Hazardous waste; Hydrocarbon

Pyrolysis characteristics and kinetics of acid tar waste from crude benzol refining: A thermogravimetry-mass spectrometry analysis

Pyrolysis is an attractive thermochemical conversion technology that may be utilised as a safe disposal option for acid tar waste. The kinetics of acid tar pyrolysis were investigated using thermogravimetry coupled with mass spectrometry under a nitrogen atmosphere at different heating rates of 10, 15 and 20 K min(-1). The thermogravimetric analysis shows three major reaction peaks centred around 178 degrees C, 258 degrees C, and 336 degrees C corresponding to the successive degradation of water soluble lower molecular mass sulphonic acids, sulphonated high molecular mass hydrocarbons, and high molecular mass hydrocarbons. The kinetic parameters were evaluated using the iso-conversional Kissinger-Akahira-Sunose method. A variation in the activation energy with conversion revealed that the pyrolysis of the acid tar waste progresses through complex multi-step kinetics. Mass spectrometry results revealed a predominance of gases such as hydrogen, methane and carbon monoxide, implying that the pyrolysis of acid tar waste is potentially an energy source. Thus the pyrolysis of acid tar waste may present a viable option for its environmental treatment. There are however, some limitations imposed by the co-evolution of corrosive gaseous components for which appropriate considerations must be provided in both pyrolysis reactor design and selection of construction materials