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Ontogenesis of intestinal transport of 5-methyltetrahydrofolate in the rat
Insights
The intestinal transport of 5-methyltetrahydrofolate (5-CH3H4-PteGlu) is fully developed in young rats. Transport efficiency decreases with age due to reduced carrier activity or number, not affinity.
Area of Science:
- Biochemistry
- Physiology
- Developmental Biology
Background:
- Intestinal folate absorption is crucial for health.
- Understanding the developmental changes in nutrient transport is important.
Purpose of the Study:
- To investigate the developmental changes in the intestinal transport of 5-methyltetrahydrofolate (5-CH3H4-PteGlu) in rats.
- To characterize the transport mechanism and its age-related alterations.
Main Methods:
- Utilized the everted-sac technique in suckling, weanling, and adult rats.
- Assessed 5-CH3H4-PteGlu transport rates, pH dependence, and jejunum vs. ileum differences.
- Analyzed kinetic parameters (Vmax, Kt) and carrier-mediated transport characteristics.
Main Results:
- 5-CH3H4-PteGlu transport was active, saturable, and dependent on energy, temperature, and sodium.
- Transport rates decreased significantly with age (suckling > weanling > adult).
- Vmax decreased with maturation, while apparent Kt remained similar across age groups.
Conclusions:
- The intestinal transport system for 5-CH3H4-PteGlu is mature by the suckling stage in rats.
- Maturation leads to a decrease in transport capacity, likely due to reduced carrier number or activity, not altered substrate affinity.
Abstract:
Developmental aspects of the intestinal transport of 5-methyltetrahydrofolate (5-CH3H4-PteGlu) were studied in suckling (14-day-old), weanling (22-day-old), and adult (90-day-old) rats by use of the intestinal everted-sac technique. Mucosal-to-serosal transport of 0.5 microM 5-CH3H4PteGlu was linear with time for 40-min incubation and occurred at a rate of 0.035, 0.032, and 0.010 nmol X g initial tissue wet wt-1 X min-1 for suckling, weanling, and adult rats, respectively. The transport of 5-CH3H4PteGlu in all age groups was pH dependent (maximal at pH 6) and was higher in the jejunum than in the ileum. In all age groups the transport of 5-CH3H4PteGlu occurred by an active carrier-mediated system. The system was saturable; energy, temperature, and Na dependent; inhibited by structural analogues; and capable of accumulating the substrate against a concentration gradient. Kinetic parameters of the transport process, however, showed some difference. A progressive decrease in Vmax was observed from suckling to weanling to adult rats (5.1, 3.7, and 0.8 nmol X g initial tissue wet wt-1 X 30 min-1, respectively), while apparent Kt was similar (2.2, 1.73, and 1.79 microM, respectively). This study demonstrates that the transport system of 5-CH3H4PteGlu in the rat is fully developed at the suckling age. The results also suggest that the activity and/or the number, but not the affinity, of the transport carriers decrease with maturation.