Growth hormone responses to thyroid hormone in the neonatal rat: resistance and anamnestic response
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Summary
This summary is machine-generated.Neonatal hypothyroidism in rats does not affect growth hormone (GH) levels initially, but sensitivity to thyroid hormone (T3) develops later. Secondary T3 stimulation shows a faster GH response than primary stimulation.
Area Of Science
- Endocrinology
- Developmental Biology
- Molecular Endocrinology
Background
- Thyroid hormones are crucial for mammalian development and metabolic regulation.
- Neonatal hypothyroidism can lead to impaired growth and developmental deficits.
- Growth hormone (GH) synthesis and secretion are known to be influenced by thyroid hormones.
Purpose Of The Study
- To investigate the developmental acquisition of growth hormone (GH) responsiveness to triiodothyronine (T3) in neonatally thyroid-deprived rats.
- To compare the effects of primary and secondary T3 stimulation on GH synthesis and GH messenger RNA (mRNA) activity.
- To determine the timing of GH dependence on thyroid hormone during early life.
Main Methods
- Neonatal hypothyroidism induced in rat pups using an iodine-deficient, propylthiouracil-containing diet.
- Triiodothyronine (T3) administered via subcutaneous injection for primary and secondary stimulation.
- Measurement of pituitary GH content, in vitro GH synthesis rate, and GH mRNA activity using cell-free translation.
Main Results
- Hypothyroid pups showed growth arrest and decreased pituitary GH content from 10 days of age.
- GH synthesis and GH mRNA activity were significantly elevated after both primary and secondary T3 stimulation in hypothyroid rats.
- Secondary T3 stimulation resulted in a 2.5-fold faster response in GH synthesis and mRNA activity compared to primary stimulation.
- GH responsiveness to T3 was acquired between 6 and 10 days of neonatal life.
Conclusions
- Growth hormone accumulation in neonatal rat pituitaries is initially independent of thyroid hormone.
- Sensitivity to thyroid hormone for GH regulation is established between the 6th and 10th postnatal days.
- Secondary T3 stimulation elicits an enhanced, anamnestic response in GH synthesis and mRNA activity, similar to adult responses.