Differentiation of frog skin active Na+ transport during metamorphosis is induced by thyroid hormone

Hormonal control of differentiation of the active Na+ transport system across the skin of the Rana catesbeiana tadpole during metamorphosis was investigated. Active Na+ transport in the tadpole does not operate before climax stages (stage XX) because of the lack of a Na+ channel, even though the skin already has a Na+ pump. Injection of aldosterone (200 nmol/kg body wt), corticosterone (500 nmol/kg body wt), or hydrocortisone (300 nmol/kg body wt) at stages XIII-XV and administered for 2 weeks neither induced differentiation of the Na+ channel nor stimulated the Na+ pump. On the other hand, differentiation of the Na+ channel (increase in active Na+ transport) was induced by thyroid hormone without supplementary mineralicorticoid or glucocorticoid treatment. Triiodothyronine (10 nmol/kg body wt every other day for 2 weeks) increased Na+ channel density, even when the mineralicorticoid antagonist spironolactone (20 mumol/kg body wt) or glucocorticoid antagonist metyrapon (442 nmol/kg body wt) were injected. The skin active Na+ transport system acquires aldosterone sensitivity only after differentiation of the Na+ channel is induced by thyroid hormone.