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Changes in the hypothalamic-pituitary somatotropic function of infant hypothyroid rats
V De Gennaro Colonna1, G Bertola, C B Coco
1Department of Pharmacology, University of Milan, Italy.
Summary
Infant hypothyroidism in rats affects growth hormone (GH) regulation. While GH-releasing hormone (GHRH) system changes appear later, somatostatin (SS) neurons show less sensitivity to thyroid axis disruption.
Area of Science:
- Endocrinology
- Neuroscience
- Developmental Biology
Background:
- The pituitary-thyroid axis is crucial for development and regulates growth hormone (GH) secretion.
- Hypothyroidism during development can impact neuroendocrine systems controlling GH release.
Purpose of the Study:
- To investigate the effects of developmental hypothyroidism on GH-releasing hormone (GHRH) and somatostatin (SS) neuronal systems.
- To determine the timing and nature of functional changes in these regulatory systems.
Main Methods:
- Rats were made hypothyroid using propylthiouracil from parturition.
- Plasma GH, thyroid-stimulating hormone (TSH), and hypothalamic GHRH/SS levels and mRNA were measured at 14 and 21 days.
- Hypothyroid and age-matched control groups were compared.
Main Results:
- Hypothyroid rats exhibited elevated TSH and decreased GH levels at both ages.
- At 14 days, no differences in hypothalamic GHRH/SS were observed.
- At 21 days, hypothyroid rats showed reduced GHRH content and increased GHRH mRNA, while SS remained unchanged.
Conclusions:
- Functional changes in the GHRH system emerge later than GH secretion deficits in infant hypothyroid rats.
- These GHRH alterations appear dependent on GH deficiency.
- Somatostatin neurons demonstrate lower sensitivity to pituitary-thyroid axis perturbations during development.