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Postnatal development of corticosteroid-binding globulin: effects of thyroxine
Endocrinology
|November 1, 1982
Summary
Thyroxine (T4) increases corticosteroid-binding globulin (CBG) in pups, with the response depending on age. T4 is crucial for initiating and sustaining CBG levels by stimulating its hepatic synthesis.
Area of Science:
- Endocrinology
- Developmental Biology
- Biochemistry
Background:
- Corticosteroid-binding globulin (CBG) plays a vital role in regulating corticosteroid bioavailability.
- Thyroid hormones, particularly thyroxine (T4), are known to influence various physiological processes during development.
Purpose of the Study:
- To investigate the age-dependent temporal and dose characteristics of the corticosteroid-binding globulin (CBG) response to thyroxine (T4).
- To determine if T4 stimulates the hepatic biosynthesis of CBG.
Main Methods:
- Hypothyroid pups (induced by n-propylthiouracil) were administered single or multiple injections of T4 at different postnatal ages.
- Dose-response studies were conducted to assess T4's effect on CBG levels.
- In vitro liver slice systems were used to measure CBG production.
Main Results:
- The CBG response to T4 was age-dependent, with older pups (day 7) showing a significant increase compared to younger pups.
- Older pups exhibited higher maximum CBG concentrations (Rmax) but similar sensitivity (D1/2) to T4.
- T4 administration was required to initiate and sustain the developmental rise in CBG, and withdrawal led to maintenance of elevated levels.
Conclusions:
- The T4-induced CBG response is primarily influenced by the animal's age, specifically affecting the Rmax rather than sensitivity.
- Thyroxine is essential for both initiating and maintaining the developmental increase in CBG.
- T4 stimulates hepatic CBG synthesis, leading to increased circulating CBG levels.