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Thyroxine effect on intestinal Cl-/HCO3- exchange in hypo- and hyperthyroid rats
A Tenore1, A Fasano, N Gasparini
1Department of Pediatrics, University of Udine School of Medicine, DPMSC, Italy.
The Journal of Endocrinology
|December 1, 1996
Summary
Thyroid hormones significantly impact intestinal function. Hypothyroidism increases ion absorption and transit time, while hyperthyroidism decreases chloride transport, explaining associated constipation and diarrhea.
Area of Science:
- Gastroenterology
- Endocrinology
- Physiology
Background:
- Thyroid dysfunction is associated with gastrointestinal motility disorders, including constipation and diarrhea.
- The precise mechanisms linking thyroid hormones to intestinal electrolyte transport remain incompletely understood.
Purpose of the Study:
- To investigate the role of thyroid hormones in regulating transepithelial water and electrolyte transport in the small intestine.
- To correlate changes in thyroid physiology with alterations in intestinal function and motility.
Main Methods:
- Pharmacological induction of hypothyroidism and hyperthyroidism in Albino Wistar rats.
- In vitro measurement of ion net fluxes in rat small intestine using Ussing chambers under short-circuit conditions.
- Correlation analysis between serum L-thyroxine (T4) levels and measured ion transport parameters.
Main Results:
- Hypothyroid rats exhibited increased intestinal transit time, enhanced chloride absorption, and elevated residual ion flux (indicating bicarbonate secretion).
- Hyperthyroid rats demonstrated decreased mucosal-to-serosal chloride transport.
- Significant negative correlations were observed between serum T4 levels and net chloride transport (r = -0.74) and residual ion flux (r = -0.55).
Conclusions:
- Thyroid hormones (T4) inhibit chloride/bicarbonate anion exchange, influencing transepithelial transport and intestinal motility.
- The observed effects on electrolyte transport likely require protein synthesis, as acute T4 addition did not yield similar results.
- These findings provide an in vitro explanation for the clinical manifestations of constipation and diarrhea in hypothyroidism and hyperthyroidism, respectively.