The duration of enzyme induction in orocaecal transit time measurements.

OBJECTIVE

In this study, the duration of enzyme induction provoked by unlabelled lactose ureide (LU) in orocaecal transit time (OCTT) measurements with lactose-[(13)C]ureide ((13)C-LU) was evaluated.

DESIGN

Experimental study.

SETTING

University of Rostock, Children's Hospital, Research Laboratory.

SUBJECTS

Fifteen healthy adults aged 19-54 years.

INTERVENTION

One-half gram of (13)C-LU was administered together with a continental breakfast. After 1 week, the test was repeated after pre-dosing of 5 x 100 mg LU on the day before the study began. The (13)C-LU ingestion was repeated under identical conditions but without pre-dosing 1 and 3 weeks after pre-dosing. Expired air samples were taken over 14 h. (13)CO(2)-enrichment was measured by isotope ratio mass spectrometry (SerCon, Crewe, UK). The OCTT was calculated from the interval between (13)C-LU administration and the detection of a significant and sustained (13)C-rise of 2 delta over baseline in breath.

RESULTS

Without pre-dosing, an OCTT of 419+/-82 min was measured. The pre-dosing resulted in higher (13)C-enrichments and caused a significant OCTT shortening of 311+/-99 min (P=0.028). One and 3 weeks after pre-dosing, the measured OCTT again increased to 404+/-124 and 379+/-103 min, respectively.

CONCLUSIONS

Pre-dosing with LU before pulse labelling with (13)C-LU led to an induction of enzyme activity and resulted in a definitive estimation of the OCTT when using a threshold of 2 delta over baseline. After 1 and 3 weeks, respectively, the OCTT was no longer significantly different to those without pre-dosing, indicating the disappearance of enzyme induction. Therefore, a pre-dosing with LU on the day before (13)C-LU ingestion is essential for OCTT measurements.