Examination of
glucose kinetics, pancreatic alpha and beta cell function, plasma
lipids, urinary acidification and
calcium excretion has been undertaken in a patient with
hereditary fructose intolerance. This case was unusual as it was associated with
insulin-requiring diabetes, type IV
hyperlipemia,
hypercalciuria and
renal calculi. He also demonstrated the previously described
fructose-induced defect of urine acidification.
Glucagon and
C-peptide assays showed that the pancreatic alpha cells were stimulated by
fructose and that the beta cells did not respond to
fructose. It is not known whether the latter was due to his diabetes or to the lack of a beta cell response to this
sugar. Primed 14C-glucose infusions were used for the first time to study nonsteady state
glucose kinetics in man. They showed that, 24 hours after the last
insulin injection and under basal conditions, the
glucose concentrations increased because
glucose production exceeded
glucose utilization. However, after the administration of
sorbitol the plasma
glucose concentration decreased because
glucose production decreased. After the administration of
sorbitol there was no change in the metabolic clearance of
glucose. This reflects the lack of a peripheral
insulin effect and is consistent with the lack of any measurable
C-peptide.
Glucose utilization also decreased, but this decrease was less than the decrease in
glucose production. Because the metabolic clearance of
glucose remained unchanged, it was concluded that the change in
glucose utilization was solely due to the decrease in
glucose concentration. The absence of
C-peptide in the plasma indicated that changes in
glucose turnover were not related to any changes in endogenous plasma
insulin. Furthermore, the plasma
glucagon concentration increased and, hence, changes in this
hormone could not account for the decrease in
glucose production. Therefore, it was concluded that the
sorbitol-induced decline in
glucose production was due to a direct effect on hepatic metabolism.