Dec 9 (Reuters) - United Therapeutics Corp said it received a subpoena from the U.S. Department of Health and Human Services regarding marketing practices used to sell three of its drugs to treat pulmonary arterial hypertension (PAH).

The subpoena, which follows an investigation by the Department of Justice, requires the company to submit documents regarding its Remodulin injection, Tyvaso inhalation solution and Adcirca tablets, the company said on Monday.

These three drugs are the only treatments for which United Therapeutics holds marketing approval from the U.S. Food and Drug Administration, according to the company's website.

PAH is increased pressure in the arteries of the lungs. These arteries carry blood from the heart to the lungs to pick up oxygen.

The company said it planned to cooperate with the investigation.

Shares of the Silver Spring, Maryland-based company closed at $90.97 on the Nasdaq on Friday.