It is all here:
note links and diagrams
Unless pregnenolone is low, there would be no reason to take it as a supplement. If low that can be from low LH and/or other imbalances that affect the mitochondria. Increasing pregnenolone or DHEA from normal to high levels will not increase hormones that are under feedback control. And in some [rare] cases, can increase estrogens and thus drive down T levels.
The http://en.wikipedia.org/wiki/Mitochondrion are the foundation of your metabolism and also produce pregnenolone. Pregnenolone levels can be considered a measure of metabolic fitness.