Schiller L R, Emmett M, Santa Ana C A, Fordtran J S
Department of Internal Medicine, Baylor University Medical Center, Dallas, Texas.
Gastroenterology. 1988 Apr;94(4):933-41. doi: 10.1016/0016-5085(88)90550-1.
Polyethylene glycol (PEG) has been used to increase the osmotic pressure of fluids used to cleanse the gastrointestinal tract. However, little is known about its osmotic activity. To investigate this activity systematically, solutions of PEG of differing molecular weights were made and subjected to measurement of osmolality by both freezing point depression and vapor pressure osmometry. Measured osmolality was increasingly greater than predicted from average molecular weight as PEG concentration increased. Measurement of sodium activity in NaCl/PEG solutions by means of an ion-selective electrode suggested that the higher than expected osmolality could be due in part to interactions that, in effect, sequestered water from the solution. Osmolality was consistently greater by freezing point osmometry than by vapor pressure osmometry. To determine which osmometry method reflected biologically relevant osmolality, normal subjects underwent steady-state total gut perfusion with an electrolyte solution containing 105 g/L of PEG 3350. This produced rectal effluent that was hypertonic by freezing point osmometry but isotonic by vapor pressure osmometry. Assuming that luminal fluid reaches osmotic equilibrium with plasma during total gut perfusion, this result suggests that the vapor pressure osmometer accurately reflects the biologically relevant osmolality of intestinal contents. We conclude that PEG exerts more of an osmotic effect than would be predicted from its molecular weight. This phenomenon may reflect interactions between PEG and water molecules that alter the physical chemistry of the solution and sequester water from the solution.
聚乙二醇（PEG）已被用于提高用于清洁胃肠道的液体的渗透压。然而，关于其渗透活性的了解却很少。为了系统地研究这种活性，制备了不同分子量的PEG溶液，并通过冰点降低法和蒸气压渗透法测量其重量摩尔渗透压浓度。随着PEG浓度的增加，测得的重量摩尔渗透压浓度越来越高于根据平均分子量预测的值。通过离子选择性电极测量NaCl/PEG溶液中的钠活性表明，高于预期的重量摩尔渗透压浓度可能部分归因于相互作用，这种相互作用实际上从溶液中隔离了水。通过冰点渗透压法测得的重量摩尔渗透压浓度始终高于通过蒸气压渗透压法测得的结果。为了确定哪种渗透压测量方法反映了生物学相关的重量摩尔渗透压浓度，正常受试者用含有105 g/L PEG 3350的电解质溶液进行稳态全肠道灌注。这产生的直肠流出物通过冰点渗透压法测定为高渗，但通过蒸气压渗透压法测定为等渗。假设在全肠道灌注期间管腔内液体与血浆达到渗透平衡，该结果表明蒸气压渗透压计准确反映了肠内容物的生物学相关重量摩尔渗透压浓度。我们得出结论，PEG发挥的渗透作用比根据其分子量预测的要大。这种现象可能反映了PEG与水分子之间的相互作用，这种相互作用改变了溶液的物理化学性质并从溶液中隔离了水。
