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/p hlorizin hydrolase (LPH) mRNA accumulation along with a rise in lactas e activity in rat jejunum [Goda, Yasutake, Suzuki, Takase and Koldovsk y (1995) Am. J. Physiol. 268, G1066-G1073]. To elucidate the mechanism s whereby dietary carbohydrates enhance the LPH mRNA expression, 7-wee k-old rats that had been fed a low-carbohydrate diet (5.5 % of energy as starch) were given diets containing various monosaccharides or sucr ose for 12 h. Among carbohydrates examined, fructose, sucrose, galacto se and glycerol elicited an increase in LPH mRNA accumulation along wi th a rise in lactase activity in the jejunum. By contrast, glucose and a-methylglucoside were unable to elicit a significant increase in LPH mRNA levels. To explore a transcriptional mechanism for the carbohydr ate-induced increases in LPH mRNA levels, we employed two techniques c urrently available to estimate transcriptional rate, i.e. RNA protecti on assays of pre-mRNA using an intron probe, and nuclear run-on assays . Both assays revealed that fructose elicited an increase in transcrip tion of the LPH gene, and that the transcription of LPH was influenced only slightly, if at all, by glucose intake. These results suggest th at 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-i nduced increase of LPH mRNA expression.