Hmmm....I have some couplings as well. I don't know if they are "high pressure" or not. I got them from a local shop specializing in tubing and associated hardware.
I don't know what they are rated at, but I walked in with the line in hand asking to order a new one and they said "are you sure, we just use these".
The line only pressurizes to about 210 PSI when the system is making adjustments and filling the reservoir then depressurizes.