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The glucose substitutes (fructose, sorbitol, xylitol) have significant metabolic advantages in stress situations as compared to glucose. Side-effects are usually not to be expected if indications and dosage are carefully determined. The only contraindication for fructose and for sorbitol is hereditary fructose intolerance. However, this metabolic disease should be known to physicians who are involved in parenteral nutrition. Fructose intolerance might also be diagnosed by the metabolic alterations caused by fructose or by sorbitol administration in such patients. It was shown repeatedly during the last few decades that glucose formed in the liver during metabolism of glucose substitutes and delivered to the circulation is obviously metabolized without an increase in blood glucose concentration and without additional requirement of insulin. No explanation for this amazing, long-observed metabolic effect is known to date. These reproducible results should stimulate new investigations. Such effects should not be rejected or questioned because they do not fit into the hypotheses.

Significant rise of fructose in the blood plasma of cattle resulted from an application of sorbite solution (0.5 g sorbite per kg live weight), with its onset as early as during the infusion. The highest concentration was reached 15 minutes after completion of infusion. Rise in glucose (11 mg/100 ml plasma on average) failed to prove statistically significant and dropped temporarily (after 60 to 120 minutes) below the original value. The lactate level in the blood went up temporarily and reached its maximum 30 minutes from the end of infusion. Sorbite solution (1 g/kg live weight) was intravenously applied to sheep and tock fructose to its maximum after 30 minutes. Intraperitoneal application of sorbite solution (1 g/kg live weight) was tolerated well also by piglets and triggered an age-dependent decline of glucose in blood plasma.

An enzymatic endpoint determination of xylitol and sorbitol by the use of L-iditol dehydrogenase is described. Despite the use of pH 9 and the addition of semicarbazide, the reaction goes only 80% to completion. Therefore a standard value has to be used. The lower limit for measurement of concentrations in serum is around 0.1 mmol/l. The most favorable range is between 0.4 and 1.2 mmol/l with a coefficient of variation of below 4%. Sensitivity and precision is higher than with the kinetic method described earlier. Further simplification for the routine control of infusion therapy with polyols is suggested.

Basic caloric needs of patients with compensated liver cirrhosis and healthy controls were supplied for 48 h with mixtures of glucose, fructose, sorbite, and xylit. Mixed solutions (20% w/v) containing glucose + fructose (n = 6), glucose + sorbite (n = 36), glucose + xylit (n = 37) in a 1:1 ratio, and glucose + fructose + xylit (n = 6) in a 1:2:1 ratio as well as glucose alone (n = 6) were administered in a dosage of 0.25 g/kg/h each. Utilization of the monosubstances, corresponding blood levels, and the effects on parameters of carbohydrate and lipid metabolism were frequently controlled. In contrast to mixed solutions, infusion of glucose alone caused a pronounced increase of the insulin levels and hyperglycemia in some patients suffering from liver cirrhosis. In both groups infusion of glucose + xylit was accompanied by a rise of uric acid levels. In liver cirrhotics a permanent decrease of phosphate as well as an increase of xylit concentrations were observed. These changes were not seen with xylit lowered to 50%, in glucose + fructose + xylit infusion. Therefore, we recommend to restrict xylit in liver cirrhotics to 100/24 h. No significant changes of blood gas measurements, ph values, hyperlactatemia, or lactic acidosis were seen. There was no difference in the anticatabolic, antilipolytic, and antiketogenic effect of the solutions. The least changes of all controlled parameters were observed with glucose + fructose and glucose + fructose + xylit infusions.

Glucose, fructose, sorbitol or xylitol were infused for four hours at different dose levels to metabolically healthy volunteers. The metabolic effects of the so-called glucose substitutes were compared to that of glucose. Even at very high doses (2.0 g/kg bodyweight per hour) of infusion of glucose or fructose a steady state was attained. This, however, was not the case with xylitol or sorbitol at lower doses (i.e. 0.5 g/kg bodyweight per hour), where no steady state was reached. The blood glucose concentration is not influenced by any of the glucose substitutes. During infusion of very high doses of fructose a small increase in serum insulin level is found, however, without any alteration in blood glucose concentration. Glucose as well as glucose substitutes cause an immediate suppression of free fatty acid concentrations in serum. In case of glucose there is a manifold increase in fatty acid concentration after the infusion is terminated. On the other hand, the free fatty acid concentration remains low even several hours following termination of the high-dosed fructose infusion. Theoretically one would expect an increase in triglyceride concentration, at least at the high dosed carbohydrate infusions. In contrast to this theoretical expectation, in the case of glucose and of xylitol a significant reduction of triglyceride concentration in serum was observed. Fructose and sorbitol did not exhibit this effect. Glucose and fructose are well utilized in metabolically healthy subjects. The maximum turnover rates for both polyols are lower. Unlike glucose, the glucose substitutes obviously do not cause any serious disturbation in hormonal regulations. Only in the case of glucose, counterregulation is seen following the termination of the infusion.

Different quantities of sorbite-electrolyte solution were intravenously administered to eight heads of cattle and four heads of sheep (application values being 50 g sorbite, 0.3049 g MgCl2-6H2O, 0.3728 g KCl, 0.5477 g CaCl2-6H2O, 5.265 g NaCl, 6.804 g sodium acetate-3H2O with 1,000 ml distilled water). Different rises of sorbite, fructose, and glucose were recorded from the blood plasma. Certain manifestations of incompatibility and intolerance phenomena were observed, among them increase of cardiorespiratory activity and muscular tremor. Those findings were obtained primarily from animals which exhibited also strong rise in glucose concentration. One of the sheep died. Larger quantities of solution (2,000 ml or 4,000 ml) were intraperitoneally applied to ten heads of cattle and tolerated by them with no reaction. Sorbite in blood plasma usually reached its maximum two or three hours from application, however, without any rise of fructose or glucose. Slow drip infusion or intraperitoneal infusion are the techniques recommended for application of the above sorbite-electrolyte solution to ruminants.

In seven patients with chronic renal failure in an advanced stage 17 episodes of upper abdominal pain, hypertension, vomiting and (in some of them) coma occurred during peritoneal dialysis with sorbitol-containing dialysate. The signs recurred in some of the patients but did not when glucose-containing dialysate of otherwise identical composition was used. Very high levels of sorbitol in CSF and serum were measured in the comatose patients. The precipitating factor is probably a reduced metabolic breakdown of sorbitol in renal failure with preferential intracellular deposition of sorbitol and subsequent cellular oedema. To avoid this dangerous reaction it is necessary to use glucose instead of sorbitol in peritoneal dialysates, despite the technical problems of sterilisation. Where this is not possible, glucose should be added in order to reduce the sorbitol concentration in the dialysate to less than 15g/l.

Average sorbite half-life values were 11.8 minutes in two fasting calves, 18.7 minutes in three calves after drinking, 16.4 minutes in five heads of young cattle, and 16.6 minutes in two heads of adult cattle, following intravenous injection of 0.5 g/kg live weight of sorbite solution. Sorbite conversion thus proved adequate and better than glucose conversion. Fructose levels in the blood plasma of fasting calves as well as of young and adult cattle underwent statistically significant rises, following sorbite infusion, the steepest rise being recorded from adult cattle. Significant glucose and insulin increases following sorbite infusion were recordable only from blood plasma of adult cattle. Concentrations of free fatty acids in blood plasma were quite irregular.