It’s my understanding that he didn’t put himself at risk for the adrenaline, he did it because he valued the safety of the animals he cared for above his own. I seem to remember him explaining his reasoning on his show. There are lots of devices and drugs that can be used for protected contact so that animal handlers are never put at serious risk, but all of them can and do sometimes go horribly wrong for the animals in addition to being very traumatic in ways that it can be difficult for humans to conceive. He didn’t do it without thought either, it being clear that the techniques he used required an intimate knowledge of those animals and their behaviors. He didn’t die wrestling a croc or handling a venomous snake. He died from being to close to an animal he likely had much less familiarity with.