http://www.anabolicscience.com/forums/showthread.php?threadid=10122
Other than the slight diff in price

there is a slight difference in purity. Quote from the manufacturer:
"Receptor Grade is highly purified > 95%, and often is 98% as checked by all qc methods. Media Grade is little lower quality compared to receptor grade, as the major component is similar to the receptor grade, but carries minor contaminants. The receptor grade is 98% pure and its application is to study the receptor-ligand interactions. The Media Grade material was principally formulated to be high quality inexpensive reagent for in-vivo animal studies or in serum-free or low serum cell culture conditions and other in-vitro applications."
Seems that this would indicate it
should be the same effects-wise, just not quite as "clean".
The Media Grade material was principally formulated to be high quality inexpensive reagent for in-vivo animal studies
rugger