Related Experiment Videos
Effect of carbenoxolone on glucocorticoid metabolism and Na transport in toad bladder
A S Brem1, K L Matheson, T Conca
1Division of Pediatric Nephrology, Rhode Island Hospital, Providence 02902.
Abstract:
In humans, diminished 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) enzyme activity has been associated with sodium retention and hypertension. These studies show that the toad bladder, another target tissue epithelium displaying steroid-induced sodium transport, possesses the enzyme 11 beta-OHSD. The toad urinary bladder rapidly transformed corticosterone (3 x 10(-8) M) (50% by 10 min and 90% by 180 min) with 11-dehydrocorticosterone being the major metabolite. The 11-dehydrocorticosterone produced reached an apparent plateau when the tissue incubations were repeated with higher concentrations of corticosterone (10(-7) and 10(-6) M). Carbenoxolone sodium (2.5 x 10(-5) M), a water soluble derivative of glycyrrhetinic acid, markedly inhibited the metabolism of corticosterone (3 x 10(-8) M) to 11-dehydrocorticosterone similar to previous observations in the mammalian kidney. Carbenoxolone sodium (2.5 x 10(-5) M) did not significantly affect short-circuit current (SCC) in toad bladders when added to either the serosal or mucosal bath. However, when carbenoxolone sodium was added to the mucosal bath and 60 min later corticosterone 10(-6) M was placed in the serosal bath, bladders generated a SCC 2.07 +/- 0.17 (mean +/- SE) times above base line at 360 min compared with 1.48 +/- 0.11 in bladders exposed to corticosterone alone (P less than 0.02). In parallel experiments, carbenoxolone sodium in the mucosal bath enhanced the rise in SCC induced by cortisol 10(-6) M; 1.66 +/- 0.16 times above base line at 360 min compared with 1.07 +/- 0.14 with cortisol alone (P less than 0.02). We conclude that the toad bladder contains 11 beta-OHSD and inhibition of this enzyme with carbenoxolone sodium is associated with amplification of glucocorticoid-induced transepithelial sodium transport in this tissue. However, since the quantity of 11-dehydro-product produced appears to be limited, other factors in addition to inhibition of 11 beta-OHSD may play a role in this amplification of sodium transport.
Insights
The toad bladder possesses 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) enzyme activity, which transforms corticosterone. Inhibiting this enzyme with carbenoxolone sodium amplifies glucocorticoid-induced sodium transport in toad bladders.
Area of Science:
- Endocrinology
- Physiology
- Molecular Biology
Background:
- Diminished 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) activity in humans is linked to sodium retention and hypertension.
- The toad urinary bladder, a model for steroid-induced sodium transport, exhibits 11 beta-OHSD activity.
- Understanding 11 beta-OHSD function in non-mammalian tissues can provide insights into its role in sodium homeostasis.
Purpose of the Study:
- To investigate the presence and activity of 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) in the toad urinary bladder.
- To determine the effect of carbenoxolone sodium, an 11 beta-OHSD inhibitor, on steroid metabolism and sodium transport in toad bladders.
- To explore the potential role of 11 beta-OHSD in regulating transepithelial sodium transport in response to glucocorticoids.
Main Methods:
- Incubation of toad urinary bladders with corticosterone to assess steroid metabolism.
- Measurement of metabolite formation (11-dehydrocorticosterone) using chromatographic techniques.
- Assessment of short-circuit current (SCC) to quantify transepithelial sodium transport under various experimental conditions, including the presence of carbenoxolone sodium and glucocorticoids (corticosterone, cortisol).
Main Results:
- The toad urinary bladder rapidly metabolized corticosterone to 11-dehydrocorticosterone, indicating the presence of 11 beta-OHSD activity.
- Carbenoxolone sodium significantly inhibited the conversion of corticosterone to 11-dehydrocorticosterone.
- Carbenoxolone sodium, when applied to the mucosal bath, amplified the short-circuit current (sodium transport) induced by serosal corticosterone or cortisol, suggesting a modulatory role in glucocorticoid action.
Conclusions:
- The toad bladder possesses 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) activity.
- Inhibition of 11 beta-OHSD by carbenoxolone sodium enhances glucocorticoid-stimulated sodium transport in the toad bladder.
- While 11 beta-OHSD inhibition plays a role, other factors likely contribute to the amplification of sodium transport.