Basal conditions prevail at rest when no exogenous perturbations, such as meals, are taking place. They are characterised by a state which is stable and thus predictable in time. Most commonly these conditions occur in the fasting or postprandial state. There is a widespread association of basal and steady state conditions, and indeed in non-diabetic individuals this is the case, and all of glucose production, removal and concentration are constant. Under these circumstances, the usual method of assessing glucose turnover (production = removal) is tracer infusion and Equation 6.11. Fasting glucose production - and its contribution to fasting hyperglycaemia in type 2 diabetes - has been a topic of some discussion (reviewed in Radziuk & Pye 2002). Some studies showed an increase, whereas others showed a glucose production (EGP) identical to normal, and occasionally lower. The reasons for this appeared to be the patient populations studied, the time of day at which measurements were made and the techniques, both experimental and analytical, that were used (Radziuk & Pye 2002).
Studies were therefore made without the assumption of a steady state, using Equation 6.14, to re-evaluate the nature of the fasting EGP in type 2 diabetes (Radziuk & Pye 2001, 2002). The results (Figure 6.1) showed that glycaemia was high in the morning and fell throughout the day. This was caused by a corresponding decrease in EGP, against the background of a nearly constant MCR. This contrasted with the near constant fluxes seen in control subjects and demonstrated the lack of steady state under basal conditions in diabetes.
These data appear to reveal an instability in EGP in diabetic patients. To determine how glycaemia and EGP rose to morning levels, patients fasted from 8 am on day 1 of a study until 2 pm on day 2. Glucose levels and fluxes were monitored using Equation 6.14 for the last 24 h of the study (Radziuk & Pye 2006). In contrast to controls, whose glucose levels remained near constant, it was observed that glycaemia rose spontaneously throughout the
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