PARATHYROID-HORMONE MESSENGER-RNA LEVELS ARE INCREASED BY PROGESTINS AND VARY DURING RAT ESTROUS-CYCLE

Estrogen increases parathyroid hormone (PTH) mRNA levels in vivo in ov ariectomized rats. We now show that the 19-norprogestin R-5020 given t o weanling rats or mature ovariectomized rats led to a twofold increas e in thyroparathyroid PTH mRNA levels. This increase in PTH mRNA occur red at 24 and 48 h after progesterone but not at 72 h. There were no c hanges in serum calcium. In vitro, in primary cultures of bovine parat hyroid cells, progesterone increased PTH mRNA levels threefold at 10(- 8) M and twofold at 10(-9) M after 24 h. Progesterone receptor (PR) mR NA was demonstrated in rat parathyroid tissue by in situ hybridization and in human parathyroid adenoma by immunohistochemistry. Changes in PTH mRNA levels during the rat estrous cycle were also studied. At pro estrus and estrus PTH mRNA levels were increased significantly by thre e- and fourfold compared with diestrus. Our results confirm that the p arathyroid gland is a target organ for the ovarian sex a steroids estr ogen and progesterone and are of physiological relevance as shown by t he changes during estrus.