Dietary carbohydrates enhance lactase/phlorizin hydrolase gene expression at a transcription level in rat jejunum.

We have previously shown that dietary sucrose stimulates the lactase/phlorizin hydrolase (LPH) mRNA accumulation along with a rise in lactase activity in rat jejunum [Goda, Yasutake, Suzuki, Takase and Koldovský (1995) Am. J. Physiol. 268, G1066-G1073]. To elucidate the mechanisms whereby dietary carbohydrates enhance the LPH mRNA expression, 7-week-old rats that had been fed a low-carbohydrate diet (5.5% of energy as starch) were given diets containing various monosaccharides or sucrose for 12h. Among carbohydrates examined, fructose, sucrose, galactose and glycerol elicited an increase in LPH mRNA accumulation along with a rise in lactase activity in the jejunum. By contrast, glucose and alpha-methylglucoside were unable to elicit a significant increase in LPH mRNA levels. To explore a transcriptional mechanism for the carbohydrate-induced increases in LPH mRNA levels, we employed two techniques currently available to estimate transcriptional rate, i.e. RNA protection assays of pre-mRNA using an intron probe, and nuclear run-on assays. Both assays revealed that fructose elicited an increase in transcription of the LPH gene, and that the transcription of LPH was influenced only slightly, if at all, by glucose intake. These results suggest that certain monosaccharides such as fructose or their metabolite(s) are capable of enhancing LPH mRNA levels in the small intestine, and that transcriptional control might play a major role in the carbohydrate-induced increase of LPH mRNA expression.