The credit rating agency Moody's has downgraded Martin Marietta Materials to junk status, partially in response to the Raleigh company's hostile takeover bid of rival Vulcan Materials.

Moody's announced Thursday that it was lowering Martin Marietta's credit rating to Ba1, one level below investment grade.

In explaining the downgrade, Moody's cited Martin Marietta's "willingness to take on greater financial and strategic risk than previously indicated by its unsolicited bid for Vulcan Materials Company. The rating incorporates the risk that the company may re-initiate its bid for Vulcan once allowed to do so, or may seek other, potentially debt financed, acquisitions to bolster languishing organic growth."

Moody's also said that Martin Marietta's rating would be placed on review if it reinitiates its acquisition attempt for Vulcan.

Moody's on Thursday also downgraded Birmingham-based Vulcan.

A bond-research agency upgraded its rating of Highwoods Properties after the Raleigh-based real estate developer secured a $400 million credit line.

The upgrade from Moody's Investors Service reflects Highwoods' "solid liquidity profile and improved asset quality." Moody's boosted its rating to "Baa3" from "Ba1."

"Highwoods' high quality property portfolio should help Highwoods weather what is expected to be a protracted downcycle for the office market," Moody's analysts wrote.

Highwoods is one of the Southeast's largest office landlords, with about 35.4 million square feet of property. The real-estate investment trust worked with 12 banks on its new credit line, which replaces one that was scheduled to mature in May.

The new credit facility "strengthens our ability to capitalize on strategic acquisitions and build-to-suit development opportunities that enhance long-term value for our shareholders," Highwoods CEO Ed Fritsch said in a prepared statement.

The company's shares rose 79 cents to close at $33.65 today, and are up 30 percent in the past year.

According to the city's public-information office, Standard & Poor's, Fitch Ratings and Moody's Investors Service have reaffirmed Durham's AAA credit rating -- the best that it can be in the eyes of the three main credit-rating firms.