Studies on corticoid action on the toad tadpole tail in vitro

Area of Science:

• Endocrinology
• Developmental Biology
• Amphibian Physiology

Background:

• Hormonal regulation of amphibian metamorphosis is complex.
• Thyroid hormones are known inducers of tadpole tail resorption.
• The role of adrenal corticoids in this process requires further elucidation.

Purpose of the Study:

• To investigate the in vitro effect of adrenal corticoids on tadpole tail segment shrinkage.
• To determine the synergistic or antagonistic interactions between corticoids and thyroid hormones in tail resorption.
• To explore the influence of prolactin on corticoid-mediated tail resorption.

Main Methods:

• In vitro incubation of tail segments from Bufo bufo japonicus tadpoles.
• Treatment with various steroid hormones, including deoxycorticosterone acetate (DCA), aldosterone, and corticosterone.
• Co-administration with thyroid hormones (thyroxine [T4] and triiodothyronine [T3]).
• Assessment of tail segment shrinkage and blockade by prolactin.

Main Results:

• Deoxycorticosterone acetate (DCA) significantly accelerated tail segment shrinkage only in the presence of thyroxine (T4) or triiodothyronine (T3).
• DCA-induced shrinkage was dose-dependent and absent without thyroid hormone.
• Prolactin effectively blocked tail resorption induced by DCA and T4.
• Aldosterone and corticosterone also demonstrated potent activity in accelerating tail shrinkage when T4 was present.

Conclusions:

• Adrenal corticoids potentiate thyroid hormone-induced tadpole tail resorption in vitro.
• Thyroid hormone is essential for corticoid-mediated tail resorption.
• Prolactin acts as an antagonist to this hormonal interaction.
• Specific corticoids like aldosterone and corticosterone play a significant role in amphibian metamorphosis.