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Intestinal uptake of retinol in suckling rats: characteristics and ontogeny
1Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
Insights
Retinol uptake in rat intestines is a passive carrier-mediated process. Suckling rats show higher intestinal retinol uptake than adults, suggesting changes in the uptake system during maturation.
Area of Science:
- Physiology
- Nutritional Science
- Developmental Biology
Background:
- Vitamin A (retinol) is crucial for development and health.
- Intestinal uptake mechanisms are vital for nutrient absorption.
- Understanding retinol absorption during development and maturation is important.
Purpose of the Study:
- To investigate and compare retinol uptake in the developing intestine of suckling rats versus adult rats.
- To characterize the kinetic properties and regulatory factors of retinol uptake.
- To elucidate the changes in retinol intestinal uptake associated with maturation.
Main Methods:
- Intestinal everted sac technique was used to measure retinol uptake.
- Experiments were conducted on suckling (14-15 days) and adult (90 days) rats.
- Kinetic analysis (Vmax, Km), effect of metabolic inhibitors, temperature dependence, and analogue competition were assessed.
Main Results:
- Retinol uptake was linear for 5 min and significantly higher in suckling rats compared to adults in both jejunum and ileum.
- Uptake was significantly higher in the jejunum than the ileum across both age groups.
- Retinol uptake demonstrated saturable kinetics, was not affected by metabolic inhibitors, but was partially temperature-dependent, indicating a passive carrier-mediated process.
Conclusions:
- Retinol intestinal uptake in rats is a passive carrier-mediated process, similar in suckling and adult animals.
- Maturation is associated with decreased number and/or activity and increased affinity of the retinol uptake system.
- These findings highlight developmental changes in intestinal nutrient transport mechanisms.
Abstract:
Uptake of retinol in the developing intestine of suckling rats (14-15 day old) and its maturation in adult rats (90 day old) was examined using intestinal everted sacs. Uptake of retinol (0.06 microM) in the jejunum of suckling and adult rats was linear for 5 min incubation and occurred at a rate of 31.20 and 6.98 pmol/g tissue/min, respectively. In both age groups, uptake of retinol (0.06 microM) was significantly higher (p less than 0.01) in the jejunum than the ileum. Uptake of retinol was significantly higher (p less than 0.01) in suckling rats as compared to adult rats both in the jejunum and the ileum. In both suckling and adult rats, the uptake of retinol in the jejunum was 1) saturable with a Vmax value of 19.78 and 6.24 nmol/g tissue/5 min and an apparent Km value of 16.20 and 8.19 microM, respectively, 2) not affected by metabolic inhibitors, and 3) partially temperature dependent (Q10 = 2.51 and 1.92, respectively). The structural analogues retinal (50 microM) and retinoic acid (50 microM) did not affect the uptake of [3H] retinol (0.06 microM) whereas unlabeled retinol (50 microM) caused significant (p less than 0.01) inhibition. No difference in retinol metabolism by intestinal tissue was observed in the two age groups. These results demonstrate that retinol uptake in suckling rats is similar to that of adult rats in being a passive carrier-mediated process. The results also suggest that a decrease in the number and/or activity and an increase in the affinity of the uptake system of retinol occurs with maturation.