High osmolarity

Regulation of catalase expression in eukaryotes takes place as part of a generalized response mechanism. In yeast, promoter elements of the peroxisomal catalase CTA-1 respond to glucose repression and activation by fatty acids as part of organelle synthesis. The cytosolic catalase CTT-1 responds as part of a generalized stress response to starvation, heat, high osmolarity, and H2O2, and there is even evidence of translational control mediated by heme availability 26). 

Currently available contrast agents can be classified into three different groups, high-osmolar compounds with osmolalities in the order of 1500 mosm kg low-osmolar agents with 600 - 700 mosm kg and isotonic substances with osmolaH-ties similar to that of blood (300 mosm kg ). Data for individual contrast agents are summarized in Table 2. 

As a consequence of high osmolarity, macromolecules or organelles are dehydrated resulting in altered sedimentation behavior thus, different buoyant densities for nucleic acids and mitochondria are observed in different density gradient media, as illustrated in Table 5.3. Data of some density gradient media are given in Table 5.4. 

Cidal effects can be a result of the disruption of the cell wall or membrane. Cell lysis may occur when water diffuses into the high-osmolarity bacterial cytosol through the antibiotic-induced holes in the membrane, causing the bacteria to swell and burst. Cidal effects also can occur as a consequence of inhibition of bacterial DNA replication or transcription. 

Urea concentration in the medulla plays an important role maintaining the high osmolarity of the medulla and in the concentration of urine. ADH secretion is regulated by serum osmolality and by volume status. A new class of drugs, the vaptans (see under Agents That Alter Water Excretion), are ADH antagonists. 

A well-known fact to plunge into a sweat water basin after high osmolar stress, itching and burning after first reopening of the eyes. This is well explainable by means of the severe osmolar shock of tissues and surviving nerve endings if such measures are taken. 

Water Flow through an Aquaporin Each human erythrocyte has about 2 X 105 AQP-1 monomers. If water molecules flow through the plasma membrane at a rate of 5 X 10s per AQP-1 tetramer per second, and the volume of an erythrocyte is 5 x 10 n mL, how rapidly could an erythrocyte halve its volume as it encounters the high osmolar-ity (1 m) in the interstitial fluid of the renal medulla Assume that the erythrocyte consists entirely of water. 

The molecular weights determined by gel permeation analysis in high osmolarity (155 mM), agree with the particle weights obtained by SDS gel electrophoresis or sed-mentation equilibrium in the ultracentrifuge. The ability to transform to a less compact orm in low osmolarity (5 mM) appears to be a common property of all mutarotases. 

Contrast-induced nephropathy has been defined as an increase in serum creatinine of at least 25% or an absolute increase in serum creatinine of at least 0.5 mg/dL within 48 to 72 hours of iodinated contrast administration and is associated with significant morbidity and mortality (75). Important risk factors include diabetes mellitus, chronic renal insufficiency, administration of large volumes of high osmolar contrast agents, and intravascular volume depletion. Numerous pharmacologic preventive measures have been studied, but consistent benefits have not been demonstrated. In a recent large retrospective study, preprocedural statin therapy was independently associated with a lower risk of contrast nephropathy and nephropathy requiring dialysis (76). 

CM can be classified according to osmolality, which reflects the total particle concentration of the solution (the number of molecules dissolved in a specific volume) (1,2), CM with osmolality greater than that of blood may be more difficult for the kidney to excrete. Over the past 40 years, the osmolalities of available CM have been gradually decreased to physiologic levels. In the 1950s, only high-osmolar CM (e.g., diatrizoate)... 

Choose the CM with the lowest nephrotoxic effects—Low-osmolar CM have less effect on renal function than high-osmolar CM, and isosmolar CM have less effect on renal function than low-osmolar CM (LOCM) in high-risk patients with diabetes and renal insufficiency. 

Rep, M., Krantz, M., Thevelein, J.M., and Hohmann, S., 2000, The transcriptional response of Saccharomyces cerevisiae to osmotic shock. Hotlp and Msn2p/Msn4p are required for the induction of subsets of high osmolarity glycerol pathway-dependent genes. J. Biol. Chem. 275(12) 8290-8300. 

Sundar S, Sinha PR, Agrawal NK, Srivastava R, Rainey PM, Berman JD, Murray HW, Singh VP. A cluster of cases of severe cardiotoxicity among kala-azar patients treated with a high-osmolarity lot of sodium antimony gluconate. Am J Trop Med Hyg 1998 59(1) 139 3. 

High-osmolar ionic monomers (for example amido-trizoate (diatrizoate) iodamide, iotalamate, ioxitala-mate, metrizoate)... 

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