The adipogenic function and other biological effects of insulin

Studies on experimental animals with knockout of the insulin receptor gene (Insr) in the whole body or in certain tissues and/or related genes encoding proteins involved in realization of insulin signal transduction in target cells, have made an important contribution to the elucidation of insulin regulation of metabolism, particularly fat metabolism. Since the whole insulin secreted by β-cells, together with the products of gastrointestinal tract digestion of proteins, fats, and carbohydrates reaches in the liver, the latter is the first organ on which this hormone acts. The liver employs released amino acids for synthesis of proteins, including apo-proteins for various lipoproteins. Glucose is used for synthesis of glycogen, fatty acids, and triglycerides, which enter all the organs in very low density lipoproteins (VLDL). The LIRKO mice with knockout of the insr gene in the liver demonstrated inhibition of synthesis of macromolecular compounds from amino acids, glucose, and fatty acids. Low molecular weight substances demonstrated increased entry to circulation, and together with other disorders induced hyperglycemia. In LIRKO mice blood glucose levels and glucose tolerance demonstrated time-dependent normalization and at later stages the increase in glucose levels was replaced by hypoglycemia. These changes can be well explained if we take into consideration that one of the main functions of insulin consists in stimulation of energy accumulation by means of activation of triglyceride deposition in adipose tissue. FIRKO mice with selective knockout of adipose tissue Insr were characterized by decreased uptake of glucose in adipocytes, and its transformation into lipids. However, the level of body fat in animals remained normal, possibly due to preserved insulin receptor in the liver and insulin-induced activation of triglyceride production which maintained normal levels of body fat stores, the effective functioning of adipose tissue and secretion of leptin by adipocytes during inhibition of glucose transformation into triglyceride in adipose tissue. Knockout of the Insr gene in muscles blocked glucose uptake by myocytes, but it did not induce hyperglycemia, probably due to the increase in glucose uptake by other organs, which retained the insulin receptor, and induced some increase in fat resources in adipose tissue. Similar results were obtained in mice with knockout the glucose transporter 4 GLUT4 in muscle and/or adipose tissue. Insulin microinjections in the brain, in the cerebral ventricle 4 (CVI) and mediobasal hypothalamus (MBH) did not affect the insulin levels in the general circulation, but effectively activate lipogenesis and inhibited lipolysis in adipose tissue. They induced obesity, similar to conventional obesity when the insulin levels increased. These results may serve as an additional confirmation of the importance of the adipogenic insulin function in mechanisms of regulation of general metabolism.     

Structure of the carbohydrate chain of glycosylated porcine prolactin

Cyanogen bromide and chymotryptic fragments both containing a carbohydrate chain were obtained from the glycosylated form of porcine prolactin. By means of the glycosidase hydrolysis and the Smith degradation the carbohydrate chain of the glycoprotein was shown to be of the "complex" type of N-bound oligosaccharides and identical to the chain of the luteinizing hormone.     

Recombinant DNA in the study of protein hormones

The structures of some genes of pituitary, hypothalamic and thyroid protein hormones are reviewed. Cys-elements in the 5'-enhancer area of prolactin and growth hormone genes were identified by some authors. The possibility of biosynthesis of two variants of growth hormone and two different biologically active calcitonin related peptides are considered as results of alternative pro-mRNA splicing after expression of growth hormone and calcitonin genes. LH-RH and GH-RH gene structures are presented. They code the primary structures of several peptide hormones with different biological activities. These peptides are released after proteolytic processing of high molecular weight protein precursors. The structural and functional organization of the glucocorticoid receptor is discussed.     

Growth of cultured blood cells in the presence of the cryoprotector polyethylene oxide 400

The effect of polyethylene oxide 400 (PEO-400) cryoprotector on the mitotic activity of human peripheral blood leukocytes stimulated with PHA was studied in a culture. The cytologic peculiarities of the blood cell growth on addition of PEO-400 prior to cultivation are manifested in the preservation of the transformation capacity and mitosis despite a significant reduction of the mitotic activity in comparison with control cultures.     

The translocated <Emphasis Type="Italic">Liza haematocheila</Emphasis> (Teleostei: Mugilidae) as a new host of four species of <Emphasis Type="Italic">Saturnius</Emphasis> Manter, 1969 (Digenea: Hemiuridae) within its invasive range in the Black Sea

This paper presents the first documented record of four species of Saturnius Manter, 1969 in Liza haematocheila (Temminck & Schlegel) in its invasive Pontic range. S. papernai Overstreet, 1977, S. dimitrovi Blasco-Costa, Pankov, Gibson, Balbuena, Raga, Sarabeev & Kostadinova, 2006, S. minutus Blasco-Costa, Pankov, Gibson, Balbuena, Raga, Sarabeev & Kostadinova, 2006 and Saturnius sp. are described and compared with existing data by means of multivariate morphometric analysis. The morphological and morphometric similarities between the specimens of Saturnius sp. from L. haematocheila and a small form of S. papernai from L. aurata indicate the possible existence of another, cryptic species. Although having acquired at least three species of Saturnius since its establishment in the Black Sea region, there is no evidence that a Pacific congener has been introduced with this fish. This is the first report of S. minutus from the Black Sea.     

Molecular mechanisms of the alternative lipogenic function of insulin

The review discusses the hypothesis that a major function of insulin is to stimulate triglyceride accumulation in adipose tissue and glycogen synthesis in the liver and muscles. Malfunction of insulin decreases triglyceride storage in adipose tissue, while its extreme activation induces obesity. In either case, low-molecular-weight lipid metabolites, such as oxybutyrates, ketobutyrates, ketone bodies, etc., increase in content in peripheral tissues and are utilized as a preferable substrate in energy production, thus reducing the glucose uptake in cells. Leptin inhibits the lipogenic function of insulin and prevents lipid accumulation, while leptin deficiency or a decrease in leptin activity increases the lipid production and induces obesity. Lipodystrophy decreases leptin secretion by adipocytes and facilitates the lipogenic effect of insulin, but insulin does not stimulate the triglyceride accumulation in adipose tissue in the absence of subcutaneous fat. Lipid metabolites accumulate in peripheral organs and induce lipoatrophic diabetes mellitus. The hypothesis of the alternative mechanisms of insulin functioning is consented with the data obtained in mice with a targeted knockout of the insulin receptor gene in individual organs (muscles, adipose tissue, etc.) and transgenic animals with restored expression of the gene.     

Vertebrate liver cytokeratins: a comparative study

The structure and composition of intermediate filaments isolated from liver of representatives of different vertebrate classes have been studied by electron microscopy and biochemical and immunochemical methods. It has been shown that the methodological approach for isolation of rat liver intermediate filaments can be efficiently applied to all other classes of vertebrates. The intermediate filaments studied have the same electron microscopic morphology and are species undistinguishable. The molecular weight of intermediate filament proteins varies from 40,000 to 60,000 and their isoelectric point varies from 5.0 to 6.45. Immunological investigations show that in all animals studied the intermediate filaments are built up of cytokeratins belonging to both types of keratins: type I and type II. Only one protein of the type II cytokeratins is present in all vertebrate classes, whereas in lower vertebrates two or even three type I cytokeratins contribute to the structure of liver intermediate filaments. The biochemical and immunochemical results are discussed with regard to the evolution of liver cytokeratins.     

Primary structure of whale prolactin

Two CNBr fragments of sea whale prolactin containing 69 and 41 amino acid residues, respectively, were hydrolyzed by trypsin, and the hydrolytic products were separated by the paper peptide mapping technique. The amino acid sequence of 17 homogeneous peptides was studied by the Edman method as well as by hydrolysis with carboxypeptidases A and B. Based on the experimental data and the previously published results the primary structure of sea whale prolactin made up of 199 amino acid residues was proposed.