Osmotic stress due to changes in plasma glucose and its regulation in IDDM patients

Intravenous glucose tolerance tests (30 g, 5 min, constant rate) were performed in 8 IDDM patients and in 8 controls. The consequences of the osmotic pressure, induced by glucose, were investigated. Serum choline esterase was used as an endogenous marker of serum dilution. Five minutes after the end of infusion plasma glucose was raised by 182 +/- 12 mg.dl-1 in patients and by 189 +/- 6 mg.dl-1 in controls. Choline esterase values decreased by 6.6 +/- 0.8% and 6.3 +/- 1.0% respectively, P less than 0.01 each. Calculated water shifts into the extracellular space were 924 +/- 112 ml and 882 +/- 140 ml respectively. Fifteen minutes after the end of infusion glucose decreased by 32 +/- 1 mg.dl-1 in IDDM patients and by 57 +/- 2 mg-1 in controls. Serum choline esterase recovered by 2.6 +/- 0.2% and 2.7 +/- 0.2% respectively, P less than 0.01 each, indicating comparable water correction in spite of the slower fall of glucose in IDDM patients. Water correction was more rapid than glucose fall. Diuresis (46 +/- 4 ml versus 42 +/- 3 ml) or cellular uptake of serum solutes (electrolytes, amino acids, urea, creatinine) could not explain this. It is hypothesized that accumulation of free intracellular glucose reduces the osmotic gradient and facilitates cellular water re-uptake.