It is certainly possible to insert information from your database into a Constant Contact email. You would want to take a look at Creating a Campaign for more more information on this. That will allow you to create a campaign through our API and you could choose to build the HTML from information contained in your database. Once the email is complete you can either schedule it for delivery through our user interface at www.constantcontact.com or you can do this through our API with permission from our AppConnect team. You can find more information for that in Sending and Scheduling an email.
I hope this answers your question. If you have any other questions or concerns regarding this please let me know. Thanks.