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Thyroid hormone modulates rabbit proximal straight tubule paracellular permeability
1Department of Pediatrics, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75235-9063, USA. michel.baum@utsouthwestern.edu
American Journal of Physiology. Renal Physiology
|December 3, 2003
Summary
Thyroid hormone influences chloride permeability in rabbit proximal straight tubules (PST). However, it does not fully explain developmental changes in the paracellular pathway, despite affecting solute transport.
Area of Science:
- Renal physiology
- Endocrinology
- Cellular biology
Background:
- Proximal straight tubules (PST) exhibit maturational changes in passive volume absorption.
- Thyroid hormone levels increase during maturation, potentially influencing PST function.
- Neonatal and hypothyroid rabbit PST show reduced passive volume absorption compared to adult PST.
Purpose of the Study:
- To investigate the role of thyroid hormone in developmental changes of PST paracellular permeability.
- To determine if thyroid hormone directly affects passive solute flux in PST.
- To assess whether thyroid hormone levels explain the observed developmental differences in PST paracellular permeability.
Main Methods:
- In vitro microperfusion of rabbit proximal straight tubules (PST).
- Measurement of passive chloride and mannitol permeability.
- Assessment of passive ion selectivity (P(Na)/P(Cl), P(HCO3)/P(Cl)).
- Determination of paracellular resistance using current injection and cable analysis.
Main Results:
- Hypothyroid rabbit PST demonstrated significantly lower chloride permeability and passive chloride transport compared to euthyroid controls.
- Thyroid hormone replacement normalized chloride permeability and transport in hypothyroid PST.
- Mannitol permeability was significantly reduced in hypothyroid PST compared to euthyroid and thyroid-replaced groups.
- Hypothyroid PST exhibited altered passive ion selectivity (higher P(Na)/P(Cl) and P(HCO3)/P(Cl)).
- Paracellular resistance was not significantly different between euthyroid, hypothyroid, and thyroid-replaced PST.
Conclusions:
- Thyroid hormone significantly impacts chloride permeability and transport in rabbit PST.
- Thyroid hormone does not fully account for the developmental changes observed in the PST paracellular pathway.
- While thyroid hormone influences solute flux, other factors likely contribute to developmental alterations in PST paracellular resistance and permeability.