No one has ever found significant amounts of DMT in any specific tissue (brain, heart, lungs, etc). There's been some evidence of it in the blood, although there's only been one study where the minimum technological requirements have really been met.
The fact of the matter is, we know jack about endogenous DMT. We don't know where it's made. We don't know what (if anything) it does. I like to say that, for all we know, it could be a neurohormone that regulates toenail growth rates and all the magic stuff is just a coincidence of biochemistry. Yes, there was that study in rats but: 1) it was one study in need of replication 2) rats and humans have different biochemistry 3) just because it's in the pineal gland doesn't mean that's it's doing anything (it could just be a metabolite, and 3) even if it is doing something, we have no reason to believe that thing is anything related to the 'magic' of the experience.
The science of endogenous DMT has a long way to go before anyone can make the kinds of claims that folks (including Merkaba) make all the time.
As for the rest of it: where did this idea of 'frequencies' come from? Why is that just a given in the world of new-age belief systems. To be honest, I've been had a psychedelic experience (or any out-of-body experience) where I thought 'hmm, frequencies are the best way to think about this.'
Why does no one ever talk about universal Fourier Transforms?
Blessings
~ND