The following is a quote from Pete Sisco. This is the only article I've that relates liver and pancreas performance to overtraining.
"The “Dirty Little Secret” of Strength Training
Fixed training schedules are insane. Every fixed training schedule, such as "3-days-per-week", will ultimately fail you. Here’s why. As your strength increases, your workouts become more demanding and you will require more time to recover.
The average guy sitting in front of a computer has the capacity to increase his muscular strength by 300-400%. However, recovering from physical activity puts demands on many of the body’s organs, such as the liver, kidneys and pancreas, to name but three. These organs do not have the capacity to increase their metabolic functioning by the same 300-400% your muscles can.
When you think about it, this is something you already know from experience. If you do a light workout it hardly takes anything out of you. Your recovery is swift. But when you do a grueling workout involving heavy weights and high intensity overload, it can take days to feel fully recovered.
And since the indispensable key to strength training gains is progressive overload, you must find a way to increase the intensity of every workout and allow more time to recover from that workout..."