Hyperosmotics

Until the early 1960s, laboratory iavestigators rehed on dialysis for the separation, concentration, and purification of a wide variety of biologic fluids. Examples iaclude removal of a buffer from a proteia solution or concentrating a polypeptide with hyperosmotic dialysate. Speciali2ed fixtures were sometimes employed alternatively, dialysis tubes, ie, cylinders of membrane about the si2e of a test tube and sealed at both ends, were simply suspended ia a dialysate bath. In recent years, dialysis as a laboratory operation has been replaced largely by ultrafiltration and diafiltration. 

Previous studies indicate that osmotic gradients promote membrane fusion, while hyperosmotic conditions inhibit membrane fusion during exocytosis. Consistent with this idea is the observation that the release of lysosomal enzymes from rabbit neutrophils, induced by the chemotactic peptide J -formylmethionyl-leucyl-phenylalanine (FMLP), is inhibited almost 80% in a 700-mosmol/kg medium. Inhibition is immediate (within 10 s), increases with osmolality, and is independent of the osmoticant. Neutrophils loaded with the calcium indicator indo-1 exhibit an FMLP-induced calcium signal that is inhibited by hyperosmolality. Hyperosmolality (700 mosmol/kg) increases basal calcium levels and reduces the peak of the calcium signal elicited by FMLP at concentrations ranging from 10 ° to 10 M. 

Neutrophils represent an ideal system for studying osmotic effects on exocytosis. Stimulation of cytochalasin-B-treated neutrophils with the chemotactic peptide Jlf-formylmethionyl-leucyl-phenyl-alanine (FMLP) results in a rapid compound exocytosis up to 80% of lysosomal enzymes are released within 30 s (9-14). Secretion appears to be triggered by a rise in the level of cytosolic free calcium (15-18) promoted in part by entry of extracellular calcium through receptor-gated channels and in part by release of calcium that is sequestered or bound at some intracellular site (19-21). In this presentation, we augment our previously published data (22,23), which demonstrates that lysosomal enzyme release from neutrophils is inhibited under hyperosmotic conditions and that the rise in cytosolic calcium preceding secretion is inhibited as well. 

Enteral nutrition formulas (especially hyperosmotic formulas) Infectious... 

Kanesaki, Y., I. Suzuki, S. I. Allakverdiev, K. Mikami, and N. Murata (2002). Salt stress and hyperosmotic stress regulate the expression of different sets of genes in Synechocystis sp PCC6803. Biochem Biophys... 

Intravenous solutions must be isosmotic (same osmotic pressure) with red blood cells. If red blood cells were to be exposed to an i.v. solution that was hypoosmotic (lower osmotic pressure), water would move into the cells causing them to swell and possibly lyse. If red blood cells were to be exposed to a hyperosmotic i.v. solution (higher osmotic pressure), water would move out of the cells causing them to dehydrate and shrink. Both of these conditions would damage the red blood cells and disrupt function. 

Patient discomfort is another important consideration. The stinging caused by a hypoosmotic or hyperosmotic i.v. solution is not experienced with one that is isosmotic. Intravenous injections are often prepared with 0.9% sodium chloride or 5% dextrose, both of which are approximately isosmotic with red blood cells. 

Duodenal receptors are also sensitive to the chemical composition of chyme and are able to detect the presence of lipids, excess hydrogen ion, and hyperosmotic chyme. These conditions also elicit the enterogastric reflex and release of the enterogastrones in order to decrease the rate of gastric emptying. 

Has a hyperosmotic mechanism different from that of saline cathartics... 

Mazzoni MC, Borgstrom P, Arfors KE, et al. Dynamic fluid redistribution in hyperosmotic resuscitation of hypovolemic hemorrhage. Am J Physiol 1988 255 H629. 

Glaucoma Management of open-angle (chronic simple) glaucoma may be used in combination with miotics, beta blockers, hyperosmotic agents, or carbonic anhydrase inhibitors. 

Concomitant therapy Cholinesterase inhibitors may be used in combination with adrenergic agents, -blockers, carbonic anhydrase inhibitors, or hyperosmotic agents. 

Hyperosmotic laxative PO 30-150 ml as a 70% solution Rectal 120mlasa25%-30% solution... 

Case reports have indicated an association between SSRIs and the syndrome of inappropriate secretion of antidiuretic hormone. Symptoms include lethargy, headache, hyponatremia, increased urinary sodium excretion, and hyperosmotic urine. Acute treatment of this syndrome should consist of discontinuation of the drug as well as restriction of fluid intake. Patients experiencing severe confusion, convulsions, or coma should receive intravenous sodium chloride. Elderly persons may he at a higher risk for developing this syndrome. 

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