Related Experiment Videos
Role of thyroxine on postnatal development of ileal active bile salt transport
Insights
Thyroid hormone accelerates ileal active taurocholate transport development in young rats. However, it is not essential for this process, as shown by thyroidectomy studies.
Area of Science:
- Gastroenterology
- Endocrinology
- Developmental Biology
Background:
- Postnatal development of intestinal transport systems is crucial for nutrient absorption.
- Thyroid hormones play a significant role in mammalian growth and development.
- The specific role of thyroid hormone in the development of ileal taurocholate transport remains unclear.
Purpose of the Study:
- To investigate the role of thyroid hormone in the postnatal development of active taurocholate transport in the rat ileum.
- To determine if exogenous L-thyroxine or thyrotrophic stimulating hormone (TSH) can accelerate this transport.
- To assess the impact of thyroidectomy on the development of ileal taurocholate transport.
Main Methods:
- In vitro incubation technique using Sprague-Dawley rat ileum.
- Administration of pharmacological doses of L-thyroxine or TSH to young rats.
- Surgical thyroidectomy in rats at a specific age.
- Measurement of taurocholate uptake rates, Km, and Vapp.
Main Results:
- L-thyroxine treatment led to precocious development of active taurocholate transport.
- TSH treatment did not induce active transport but increased passive uptake rates.
- Thyroidectomy did not abolish active transport but significantly reduced its apparent maximal velocity (Vapp) and increased its Km.
- Thyroid hormone appears to modulate, rather than dictate, the development of this transport system.
Conclusions:
- Thyroid hormone accelerates the postnatal development of ileal active taurocholate transport.
- This hormone is not obligatory for the development of this transport mechanism.
- Thyroid hormone influences the kinetics (Vapp and Km) of ileal taurocholate transport development.
Abstract:
The role of thyroid hormone on the postnatal development of ileal active taurocholate transport uptake was measured by an in vitro incubation technique in Sprague-Dawley rats. In 16-day-old rats treated with pharmacological doses of L-thyroxine (50 micrograms X 100 g body wt-1 X day-1 on days 10-13), ileal active transport appeared precociously whose Km was 1.60 +/- 0.48 mM and Vapp (apparent maximal velocity) was 8.09 +/- 1.14 nmol X min-1 X mg dry wt-1, while age-matched shams had only passive diffusion of taurocholate. To determine whether enhanced endogenous secretion of thyroxine was capable of stimulating development of ileal active taurocholate transport, thyrotrophic stimulating hormone (TSH) (0.5 U/100 g body wt twice daily) was given on days 10-13, with uptake measured on day 16. Following TSH treatment, only passive transport for taurocholate was observed in the ileum; uptake rates were consistently higher than those for untreated controls at each study concentration. Thyroidectomy performed at age 14 days with uptake measured at age 21 days did not ablate development of ileal active transport but resulted in a significant reduction (P less than 0.001) in the Vapp (7.39 +/- 1.10 nmol X min-1 X mg dry wt-1) and a significant increase (P less than 0.014) in Km (1.72 +/- 0.53 mM) compared with age-matched controls. Thyroid hormone does not appear to be obligatory for the postnatal development of ileal active taurocholate transport.