Guys, pretty sure they were ambushed. I don't see any of Zoro's swords drawn (looks like Nami's staff thing and Brook's cane sword are stuck in the snow).
And also, even if the pituitary hormone comment wasn't EXACTLY correct, it's more or less right (for a manga). Anterior pituitary does secrete growth hormone
He's pretty much saying that if the kids aren't normally big (ie if their GH isn't normally raised, who knows how Giant physiology works :P) then they've been experimented on to make them big (increase their GH). Sorry for the unnecessary rant, med student nearing exams lol :/