In PowerPoint 2011, you can change the direction of rotation for text contained within a shape. However you actually cannot find an option to rotate your text within a shape by 180°! Funnily enough, there are options called Rotate to 90° Counterclockwise which actually rotates your text by 270° and Rotate to 90° Clockwise which rotates your text by 90°. So, you can rotate your shape text by 90° and 270°, but there is no option to rotate your text by 180°.
Microsoft and the Office logo are trademarks or registered trademarks of Microsoft Corporation in the United States and/or other countries.