Changes in thyroid ribonucleic acid, ribonucleases and alkaline ribonuclease inhibitor.

Abstract

The thyroid of the rat, mouse, dog and pig contains an inhibitor (RI) which affects thyroid alkaline ribonuclease and bovine pancreatic ribonuclease. For thyroid ribonuclease there were two pH optima, viz. pH 5.5 and 7.5, the latter being predominantly latent activity that was released by 0.2 to 0.5 HIM parahydroxy mercuribenzoate. Low-iodine diet (LID) was fed to rats and mice and thyroid RI activity increased; the change was prevented by the inclusion of thyroid USP in the diet. Addition of propylthiouracil to the diet also resulted in enhanced thyroid RI. LID given to mice led to increases in thyroid RNA and acid ribonuclease whereas alkaline ribonuclease tended to decrease. Changes in thyroid RI activity, similar to those produced by diet, were reproduced by thyrotropin both in vivo and in vitro arid by dibutyryl cyclic AMP or theophylline in vitro, indicating that the effects probably were mediated through the cyclic AMP system. (Endocrinology 94: 74, 1974)