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Hormonal interactions with the proximal Na(+)-H+ exchanger.
1Department of Internal Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298-0160.
The American Journal of Physiology
|March 1, 1990
Summary
Hormones like alpha-adrenergic agonists and angiotensin II (ANG II) stimulate proximal tubule sodium (Na+) transport, while parathyroid hormone (PTH) and dopamine (DA) inhibit it, with synergistic effects noted between alpha 2-agonists and ANG II.
Area of Science:
- Nephrology
- Endocrinology
- Molecular Physiology
Background:
- Renal proximal tubules possess receptors for various hormones, including alpha-adrenergic, angiotensin II (ANG II), parathyroid hormone (PTH), and dopamine (DA).
- Sodium (Na+) transport in the proximal nephron is significantly mediated by the Na(+)-H+ exchanger, influenced by these hormonal signals.
Purpose of the Study:
- To investigate the interactive effects of catecholamines and peptide hormones on proximal nephron Na(+)-H+ exchange.
- To determine these interactions at both physiological and pharmacological concentrations.
Main Methods:
- Isolated rat proximal tubule segments were used to measure Na(+)-H+ exchange activity.
- Activity was assessed by quantifying 22Na+ uptake, specifically the portion inhibited by ethylisopropylamiloride (EIPA).
- Hormone preincubation and 22Na+ exposure times were optimized for steady-state measurements.
Main Results:
- Alpha-adrenergic agonists and ANG II significantly stimulated Na+ uptake, with maximal effects at 10(-6) M and 10(-12) M, respectively.
- PTH and DA inhibited Na+ uptake, with optimal concentrations at 10(-8) M and 10(-6) M.
- Synergistic Na+ uptake stimulation occurred when submaximal concentrations of alpha 2-agonists were combined with ANG II.
Conclusions:
- Hormonal regulation of proximal tubule Na(+)-H+ exchange is complex, involving both stimulatory and inhibitory pathways.
- Specific interactions, such as the synergy between alpha 2-adrenergic agonists and ANG II, highlight intricate signaling networks in renal sodium handling.