AA eventually gets converted into a whole host of catabolic products, including prostaglandin (PG) E series.
The idea behind the AA supplement is that PG F2 is obligate for muscle protein synthesis (which it seems to be), so more AA = more PG F2 = hypertrophy.
Of course more AA also = more PG E series, along with the other catabolic, and potentially aglesic, products.