Stocks that moved substantially or traded heavily Monday on the New York Stock Exchange and Nasdaq Stock Market:

NYSE

AK Steel Holding Corp., down 81 cents at $4.99

Citing weakening flat steel prices, a Goldman Sachs analyst downgraded the steel products manufacturer's stock rating to "Sell."

Centene Corp., down $7.89 at $27.58

The insurer cut its full-year earnings forecast on weak results on some of its health plans. It also expects a second-quarter loss.

Under Armour Inc., down 57 cents at $102.74

The athletic clothing and shoe maker's board approved a 2-for-1 stock split saying that the move could appeal to more investors.

Skechers USA Inc., up 59 cents at $19.88

Saying that orders for the company's shoes are rising, a Sterne Agee analyst upgraded the footwear maker's stock to a "Buy" rating.

Forest Laboratories Inc., down $1.26 at $34.43

The drugmaker cut its annual profit forecast, citing falling sales of its antidepressant Lexapro against tough generic competition.

Nasdaq

Diamond Foods Inc., down $1.53 at $18.63

The maker of Emerald Nuts and Pop Secret popcorn announced that it won't be able to file some quarterly financial reports on time.

IntegraMed America Inc., up $2.34 at $13.68

The specialty health care services company is being acquired for $168.6 million by a group led by Sagard Capital.

ZaZa Energy Corp., up 71 cents at $3.96

The oil exploration company reached an agreement with Hess that will pay ZaZa $85 million and increase its acreage in Texas.