The Effect of Thyroid Hormone on Rat Intestinal Lactase Activity During Weaning Period

Song, In Sung; Kim, Chung Yong; Jung, Hyun Chae; Lee, Dong Ho; Kim, Tae Ho; Chin, Young Joo; Chang, Dong Kyung; Lee, Kook Lae

Abstract

BACKGROUND AND AIMS: The decrease in intestinal lactase activity goes inversely with the increase in thyroid hormone level during weaning period of rat. The aim of this study is to identify whether increase in the concentration of thyroid hormone in blood before weaning period can accelerate the dechne of lactase activity and to explore its genetic regulation.
METHODS
We supplied triiodothyronin (30 pg/100 g body weight/day in 1 ml of NaOH) far 36 of 8-day-old (day 8) Sprague-Dawley rats intraperitoneally for 2 weeks (T3 group) and 1 ml of 0.01 M NaOH for the 42 controls. We quantified setum T3, mucosal lactase and sucrase activity, and lactase mRNA using cDNA probe pRLU6 on the days 8, 9, 12, 15, 18, 21 and 26 which was 5 days after the end of the injection.
RESULTS
lntestina1 lactase activities were 101, 83, 84, 72, 75, 52, and 17 mu/mg protein on the days 8, 9, 12, 15, 18, 21, and 26 in the control group, whereas 72, 58, 50, 28, 21, and 19 mu/mg protein on the days 9, 12, 15, 18, 21, and 26 in the T3 group. Decline of lactase activities in the T3 group was earlier and more steady than that in the control group. The lactase activities were not correlated with lactase mRNA levels. Sucrase activities in the T3 group were 6, 17, 32, 47, 60, and 52 mu/mg protein on the days 9, 12, 15, 18, 21, and 26, whereas those in control group did not approach 9 mu/mg protein until the day 18.
CONCLUSIONS
Early increased thyroid hormone can accelerate the change of lactase and sucrase activities during weaning petiod of rats. In addition, the decrease in lactase activites was not accornpanied by the decrease in mRNA levels. These results suggest that the genetic regulation of lactase activities occur at the post-transcriptional level.