I have recently started beta sitosterol for my enlarged prostate and I'm wondering what if any interaction there may be (beneficial or detrimental) with Ainterol PM?  

I searched the web and found nothing.

I thought beta-sitosterol was one of the main components of Pygeum bark, the stuff that some people use to reduce the size of their prostate, to try to increase precum production, and to decrease DHT hormone levels.

https://en.wikipedia.org/wiki/List_of_5%CE%B1-reductase_inhibitors

The link above shows *both* Pygeum and beta-sitosterol as 5ar inhibitors, thus reducing DHT.
The herb pygeum might also cause sexual drive problems like Finasteride (also in the above list) might cause (search for Post-Finasteride Syndrome).

Whether crashing DHT is good or bad for your specific case and circumstance, only you can tell.
I've tried large doses of Pygeum (before I knew about all this) and I think it's crashed my libido, which I'm not too happy about.

Edit: I'm also not sure what the interaction is with b-sitosterol + PM is.