CALCIUM DEPLETION STIMULATES THYROXINE RELEASE FROM THE THYROID.

Excised mouse thyroids incubated in Ca++-free medium were stimulated to release increased amounts of stable thyroxine. This stimulation of thyroxine release by incubated thyroid tissue was not additive with TSH or (Bu)2cAMP. It was reversed by norepinephrine through an alpha adrenergic receptor, similar to TSH or (Bu)2cAMP stimulation. Depletion of Ca++ did not result, however, in an increase in the concentration of cAMP in incubated thyroid glands, suggesting that its locus of action was subsequent to TSH stimulation or cAMP production.