The team used their two vacant roster spots to activate running back Kevin Faulk and defensive end Brandon Deaderick.
The Patriots -- who rank at the bottom of the league in pass defense -- are left with six defensive backs on their roster. Only two -- Devin McCourty and Kyle Arrington -- have significant starting experience.
Dowling, selected in the second round of April's draft, appeared in two games this season, both as a starter. A hip injury has kept him out of action since Week 2 and now will cut short his first season.