THE INHIBITORY EFFECT OF NORADRENALINE ON THYROTROPIN-STIMULATED 3,5,3'-TRI-IODOTHYRONINE AND THYROXINE RELEASE IS MEDIATED THROUGH A CA2-DEPENDENT PROCESS IN THE THYROID-GLAND OF THE MOUSE()

We examined the effect of noradrenaline on the release of 3,5,3'-tri-i odothyronine (T3) and thyroxine (T4) from perifused mouse thyroid. Nor adrenaline suppressed the thyrotrophin (TSH)-stimulated release of T3 and T4. The addition of prazosin, which is a specific alpha1 antagonis t, or the depletion of Ca2+ from the perifusion buffer completely abol ished the inhibitory effect of noradrenaline on TSH-stimulated T3 and T4 release. Noradrenaline did not inhibit TSH-stimulated cyclic adenos ine 3',5'-monophosphate (cAMP) release in the presence of 3-isobutyl-1 -methylxanthine (IBMX), which inhibits both cAMP-specific and calmodul in-sensitive phosphodiesterases. Noradrenaline significantly suppresse d the TSH-stimulated release of T3 and T4 in the presence of IBMX. The se results suggest that the inhibitory effect of noradrenaline on TSH- stimulated T3 and T4 release is not mediated through a cAMP-dependent process or the activation of a calmodulin-sensitive phosphodiesterase, and that this inhibition is mediated through a Ca2+-dependent process regulated by the alpha1-adrenergic system in the mouse thyroid.