welcome to our site, so sorry to read about Adrian's problems. we are not Vets on this site I will give you a link to our Expert forum where perhaps they can give you more help.
http://www.medhelp.org/forums/Animal-Health---General/show/112?controller=forums&action=show&id=112&camp=msc
I will also include another link to a site with limited info, I do hope your research can lead to something.
I will ask what is Adrian's diet?
could this be a dietary intolerance b/c you did mention..alot of gas which makes me suspect. is he on a good brand of canned food with NO GRAIN? since grains are often the culprits in many dietary allergies. It may help to try changing the brand of food you are feeding....
here are a couple links, please post again if we can help or to update us...we are hoping a resolution can soon be found♥
http://www.petplace.com/cats/hematochezia-blood-in-stool-in-cats/page1.aspx
http://www.catinfo.org/