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Lipid and carbohydrate metabolism in euthyroid and hypothyroid chick embryo (Gallus domesticus)
1Department of Pharmacology, Veterans Administration Medical Center, Syracuse, NY.
Insights
Propylthiouracil (PTU) induced hypothyroidism in chick embryos significantly altered carbohydrate and lipid metabolism. Hypothyroid embryos showed lower glucose and higher phospholipids, with no change in liver lipids compared to controls.
Area of Science:
- Endocrinology
- Developmental Biology
- Metabolic Research
Background:
- Thyroid hormones are crucial for regulating metabolism in developing organisms.
- Propylthiouracil (PTU) is a known inhibitor of thyroid hormone synthesis.
- Chick embryos provide a valuable model for studying early metabolic development.
Purpose of the Study:
- To investigate the impact of PTU-induced hypothyroidism on carbohydrate and lipid metabolism in chick embryos.
- To understand how thyroid hormone deficiency affects key metabolic pathways during embryonic development.
Main Methods:
- A single dose of PTU (250 µg/embryo) was administered on day 11 of incubation.
- Embryos were sacrificed on day 20 for analysis.
- Measurements included thyroid gland weight, plasma thyroxine, plasma glucose, plasma phospholipids, and liver lipid and glycogen concentrations.
Main Results:
- PTU administration significantly enlarged thyroid glands (6-fold) and caused growth retardation.
- Plasma thyroxine levels were decreased in hypothyroid embryos.
- Hypothyroid embryos exhibited lower plasma glucose and significantly higher plasma phospholipids.
- Liver lipid concentrations were similar between control and hypothyroid embryos but higher than in young chicks.
- Unlike post-hatching PTU treatment, liver glycogen levels were not increased in hypothyroid chick embryos.
Conclusions:
- PTU-induced hypothyroidism in chick embryos leads to distinct alterations in carbohydrate and lipid metabolism.
- The embryonic metabolic response to hypothyroidism differs from that of post-hatching chicks, potentially due to the high lipid nutrient environment.
- These findings highlight the critical role of thyroid hormones in regulating embryonic metabolism.
Abstract:
1. The effect of propylthiouracil (PTU)-induced hypothyroidism on carbohydrate and lipid metabolism was studied in the chick embryo. 2. A single dose of PTU (250 micrograms/embryo) was administered on day 11 and embryos sacrificed on day 20 of incubation. 3. Thyroid glands were significantly enlarged (6 fold) by PTU administration. 4. Increased thyroid weight was associated with growth retardation and decreased plasma thyroxine levels. 5. Plasma glucose level was lower and phospholipids were significantly higher in the hypothyroid embryo. 6. Liver lipid concentrations in the control and hypothyroid embryos were not different but were significantly higher in both groups when compared to previously reported values in the young chick. 7. In contrast to PTU treatment after hatching, liver glycogen levels were not increased in the hypothyroid chick embryo. This was attributed to the high lipid nutrient condition of the chick embryo since a high lipid diet in the young chick decreased hepatic glycogen accumulation significantly.
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