I have a number of papers that describe how DMT was detected in human fluid etc. But yes there is no evidence that it is happening in the pineal gland that was an idea because melatonin which is closely related gets made there.

I recommend checking out this paper:

Endogenous psychoactive tryptamines reconsidered: an anxiolytic role for Dimethyltryptamine

authors: Jacob and Presti 2004

I will summarize some of the latest findings (sorry dont have all the papers on hand). The trace amines as DMT tryptamine and phenethylamine that are all found in the human body are now known to interact with a receptor system called the trace amine system and these compounds may be the natural endogenous ligands of this receptor system but the precise role of this system is not known yet.