aug 19 reuters  us stocks opened lower on thursday on concerns the federal reserve could begin to rein in its massive monetary stimulus while commoditylinked stocks sank as oil and metal prices tumbled to multimonth lows the dow jones industrial average dji fell 8602 points or 025 at the open to 3487467 the sp 500 spx opened lower by 1783 points or 041 at 438244 the nasdaq composite ixic dropped 10275 points or 071 to 1442316 at the opening bell