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Site of thyroxine-evoked decrease of jejunal lactase in the rat.

J T Boyle, K Kelly, L Krulich

The American Journal of Physiology

|November 1, 1982

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Thyroid hormone (L-thyroxine) reduces lactase activity in adult rat jejunum. This decrease occurs in mature enterocytes on the villus, not in newly forming cells.

Area of Science:

Gastroenterology
Endocrinology
Cell Biology

Background:

Thyroid hormones play a crucial role in regulating various physiological processes, including intestinal function.
Lactase activity is essential for lactose digestion in the small intestine.
The impact of thyroid hormones on the precise localization of lactase activity within the villus-crypt unit requires further elucidation.

Purpose of the Study:

To investigate the localization of thyroid-mediated decrease in lactase activity along the villus-crypt unit in adult rat jejunum.
To determine the temporal dynamics of this decrease following L-thyroxine administration.
To assess the role of enterocyte migration in this thyroid-induced response.

Main Methods:

Adult rats were injected with L-thyroxine, and lactase activity was measured at 24 and 48 hours.

Related Experiment Videos

[3H]thymidine was administered to track epithelial cell migration.

Serial sectioning of the jejunal villus-crypt unit and histoautoradiography were employed to localize changes in activity and cell migration.

Main Results:

L-thyroxine significantly decreased serum thyroid-stimulating hormone, food intake, and body weight within 24 hours.
Lactase activity decreased in the jejunum and midjejunum within 24 hours, localized initially to the apical villus and later extending along the entire villus.
No significant difference in epithelial cell migration was observed between control and thyroid-treated animals.

Conclusions:

Thyroid hormone administration leads to a decrease in lactase activity in mature enterocytes on the villus.
The observed decrease in lactase activity precedes significant enterocyte migration, indicating an effect on existing villus cells.
Thyroid hormones modulate lactase expression in differentiated enterocytes within the jejunal villus-crypt axis.