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Changes in parameters of growth hormone and thyrotrophic hormone, and of thyroid function, during the early postnatal
Insights
Early postnatal thyroid hormone and growth hormone (GH) interactions critically impact rat development. Disruptions during this period can permanently alter thyroid-pituitary function and impair body growth, but not brain growth.
Area of Science:
- Endocrinology
- Developmental Biology
- Physiology
Background:
- The early postnatal period is a critical window for endocrine system development.
- Thyroid hormones and growth hormone (GH) play crucial roles in mammalian growth and development.
- Thyroid-pituitary interrelations are sensitive to hormonal influences during early life.
Purpose of the Study:
- To investigate the relationship between thyroid hormones and growth hormone (GH) economy in rats during the first 10 days of life.
- To determine the impact of early postnatal hormonal changes on body, organ, and brain growth.
- To examine the critical developmental stage where thyroid hormone administration can disrupt thyroid-pituitary function.
Main Methods:
- Daily measurements of body length and weight, as well as liver, kidney, and brain weight in newborn rats.
- Determination of plasma and pituitary growth hormone (GH) and thyrotrophic hormone (TSH) levels.
- Measurement of thyroidal 127I content and plasma protein-bound iodine (PBI).
Main Results:
- Body, liver, and kidney growth rates significantly decreased between days 7-9 post-birth, correlating with changes in plasma and pituitary GH levels.
- Brain growth rate remained unaffected during this period, suggesting independence from GH economy changes.
- Progressive increases in pituitary TSH and thyroidal 125I content were observed, while plasma TSH showed no clear pattern.
Conclusions:
- Early postnatal thyroid hormone and GH interactions are crucial for normal growth patterns.
- The observed growth alterations highlight a critical developmental period sensitive to hormonal imbalances.
- Brain growth appears to be differentially regulated compared to somatic growth during this sensitive postnatal phase.
Abstract:
The body length, and the weight of the body, liver, kidney and brain have been measured daily in rats during the first 10 days after birth. The plasma and pituitary growth hormone and thyrotrophic hormone levels were also determined, as well as the thyroidal 127I content and the plasma PBI. This observation period comprises a critical stage during which administration of large doses of thyroid hormones result in a permanent derangement of the thyroid-pituitary interrelations, and impairment of body growth and pituitary GH economy. The rate of growth of body, liver and kidney has been found to decrease significantly from day 7th to 9th of post-natal age, later to increase again. The pattern of the changes observed in the plasma and pituitary GH levels during the same period might well account for the alterations in growth patterns. The rate of growth of the brain, however, is not decreased during this stage, and appears to be independent of the changes in GH economy. No clearcut pattern of changes was observed in plasma TSH level; the pituitary TSH and thyroidal 125I contents increased progressively during the entire observation period. Plasma from suckling rats often contained high concentrations of non identified iodinated compounds, which were not thyroid hormones. Results are discussed in terms of the possible relationships between thyroid hormone and GH economy during a critical developmental period.