MAMMARY 5'DEIODINASE (5'D) DURING THE BREEDING CYCLE OF THE RAT - INDIRECT EVIDENCE THAT 5'D TYPE-I IS SPECIFIC TO THE ALVEOLAR EPITHELIUM

The present study analyses the activity of 5'deiodinases type I and II in mammary gland during the breeding and estrous cycle of the rat, an d includes indirect evidence that 5'D-I is present only in the alveola r epithelium. Data show that the mammary gland exhibits 5'D-II activit y throughout the developmental period and its activity varies along th e allometric growth of the gland. 5'D-I is detected during the differe ntiation stages of the alveolar epithelium (puberty, late pregnancy) a nd its activity rises significantly (10-fold) 24 h after delivery. Dat a also show that 5'D-I activity is not present in the fat pads of the gland. These findings suggest that during its differentiation and func tional stages, the mammary gland requires an elevated and compartmenta lized production of T3.