If you don't have a previous relationship with these bloggers, then the subject line will be very important. You have to come across as delivering some value rather than a means to an end. I would recommend emailing them first and asking if it's already for you to send them your press release, to establish they are interested in receiving news releases like this from you. To get them to say it's ok, otherwise you run the risk of coming across as spamming them. Once you gain their acceptance you can ensure that what you are sending them will be well received and done something with. If you don't take the time to build the relationship, don't be surprised if they don't do anything with what you send them and you can even expect them to mark it as spam. So my best advice is to contact them and ask them very nicely if you are permitted to send them your new release to gain their permission.