Hi.
The Release endpoint will be the one you'd want to query using WSAPI (which is a REST call). Essentially you can get the information on your releases, you can apply a filter if you'd like.
You can learn more on the available fields of this endpoint if you go to: https://rally1.rallydev.com/slm/doc/webservice/ , then click the Release endpoint (in list on the left), then check the 'Child Elements' which has this endpoint's fields.
For what you asked you can simply fetch the Name, ReleaseStartDate and ReleaseDate fields.
Please let us know if that helped.
Sagi