Morgan Stanley, the second-biggest shareholder in New York Times Co., sold its entire 7.3 percent stake today, according to a person briefed on the transaction, sending the stock to its lowest in more than 10 years.

The person declined to be identified because Morgan Stanley hasn’t made the sale public yet. Traders with knowledge of the transaction said Merrill Lynch & Co. brokered a $183 million block trade of 10 million New York Times shares this morning.

Hassan Elmasry, managing director of Morgan Stanley Investment Management, unsuccessfully challenged the Sulzberger family’s control of New York Times Co. through super-voting stock that gives them a board majority. Shareholders owning 42 percent of the company, parent of the namesake newspaper and Boston Globe, withheld support for directors at the publisher’s April annual meeting.

``This guy has been speaking for a lot of people who are too discreet to speak up and challenge management,’‘ said Porter Bibb, a managing partner at Mediatech Capital Partners LLC in New York and a former New York Times Co. executive.

New York Times shares slid 54 cents, or 2.9 percent, to $18.37 at 2:51 p.m. in New York Stock Exchange composite trading and fell as low as $18.24, a level not seen since January 1997.

Other newspaper stocks, including Gannett Co., owner of USA Today, and McClatchy Co., publisher of the Miami Herald, are also trading at 10-year lows because of the loss of advertising to new media such as the Internet and the decline in classified ads linked to tumbling housing sales.