Middlesex County Sheriff Peter Koutoujian, one of five Democrats running in a special-election primary in Massachusetts’ 5th District, released his first ad of the campaign, less than three weeks before the Oct. 15 primary.

The 30-second spot touches on Koutoujian’s stance on gun control, Social Security and women’s rights. The campaign says the “six-figure buy” will air on cable and broadcast stations in the 5th District, located in the suburbs of Boston.

The special election to replace Edward J. Markey, the district’s longtime representative who was elected to the Senate earlier this year, is a wide-open contest among the five Democrats in the race.

Koutoujian and state Sens. Karen Spilka and Katherine Clark are currently in a statistical dead heat, according to a recent poll sponsored by Spilka’s campaign. In the survey, Clark leads with 19 percent, followed by Spilka with 18 percent and Koutoujian with 15 percent — and all three are within the 4.9-point margin of error.

State Rep. Carl Sciortino has climbed in the polls since he released a witty ad earlier this month, but he still lags behind the three top-tier Democrats in the contest. Sciortino is tied with state Sen. Will Brownsberger, another Democrat in the contest, each receiving 11 percent, according to the poll.

The poll was conducted by Greenberg Quinlan Rosner Research from Sept. 22 to Sept. 24. The “interactive voice response” survey — essentially an automated poll — questioned 400 likely Democratic voters in the district.

Massachusetts’ 5th District is rated a Safe Democrat contest by Rothenberg Political Report/Roll Call. Whoever wins the Democratic primary will be the successor to Markey in this strong Democratic district.