EFFECTS OF OUTDOOR AND INDOOR AIRBORNE PARTICULATE MATTER ON THYROID-HORMONE AND VITAMIN-A METABOLISM

Vitamin A is an important regulator of normal epithelial differentiati on and proliferation and might act in the promotion phase of carcinoge nesis. Vitamin A and thyroid hormone metabolism are linked by a common plasma carrier protein transthyretin (TTR). Results indicated that ex tracts of outdoor and indoor airborne particulate matter (APM), origin ating from different pollution sources, significantly interfered with thyroxine (T4) binding to TTR. The neutral fraction accounted for most of the inhibitory activity. Polycyclic aromatic hydrocarbons and nitr ated derivatives were not responsible for the activity of the neutral fraction. A single treatment of rats with an outdoor and cigarette smo ke APM extract depleted plasma T4 and triiodothyronine levels and incr eased plasma retinol levels, while liver and lung retinol levels were depleted. The studies show that APM extracts have the potency to inter fere with thyroid hormone metabolism both in vitro and in vivo and to deplete lung vitamin A in vivo.