In August 1995 Quinn et al released a study called “Interleukin-15: a novel cytokine anabolic for skeletal muscle.”
We all know most pro-bodybuilders don’t read all the new studies, but most athletes hire people that make a living by supervising professional bodybuilders and other athletes such a tennisplayers, footballplayers, cyclists etc etc.. In bodybuilding were nutrition and supplementation is very important these people are mostly called “nutritionists.”
As Dr Larkins from Australia said: "There's a whole generation of sports science people coming through who are well trained in sports performance areas and what I call genuine 
areas but many, many sports and clubs have got these people.”
Well the keywords “anabolic for skeletal muscle” did ring a bell. Of course bodybuilders already worked with other interleukins, like by example IL-6. Soon several studies on Il-15 popped up, also again from Quinn in 2002 “Overexpression of interleukin-15 Induces skeletal muscle hypertrophy in vitro.” Most studies were performed on rodents in high amounts. Thus it was hard to translate results to bodybuilders and athletes dieting and training hard.
Vascularity in bodybuilding is controversial. The term refers to the extent of superficial prominence of blood vessels, or veins, that are just below the skin’s surface. Of course, you don’t have to be a bodybuilder to show prominent vascularity. You can readily see a lot of veins on many thin people.