All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
If those secretions are saliva, then fasting is not nullified by deliberately swallowing it, but if it is something else, then you have to spit it out and not deliberately swallow it; nevertheless, if some of it involuntarily went down your throat, then this does not nullify your fast.
For more benefit, please refer to fataawa 89979and 86928.
Allaah knows best.