When does gluconeogenesis kick in during physical activity?

[Aymeric]

Hello,

I'm a dietetics student, and my course is really unclear about gluconeogenesis regulation, and exactly WHEN it happens.

What my coursebook teaches me is that glycogenolysis is the main purveyor of energy during physical exercise, and it is triggered by LOW INSULIN, HIGH GLUCAGON and HIGH ADRENALINE, which is exactly what happens when you start working out. So far so good.

But then they tell me that gluconeogenesis is triggered by LOW INSULIN, HIGH GLUCAGON and HIGH ADRENALINE, so: exactly the same conditions as above. And yet they keep saying throughout the chapter that gluconeogenesis SELDOM occurs during physical exertion itself, and that aminoacids are used only as a last resort, even though they specified a few pages before that the main substrate for GNG is alanine (followed by lactate and glycerol).

So there HAS to exist some factor that apparently delays GNG other than the aforementionned hormones, otherwise both metabolisms would start at the same time since they respond to the same hormonal changes. Right? But there is no mention of any such thing in my course.

I'm lost! If anyone could clear that up for me, I'd be really thankful.

 

[jim mcnamara]

Gluconeogensis is triggered by low blood glucose levels in tandem with increased metabolic requirements. Starvation, low carbohydrate intake, lack of glycogen are the usual precursors to gluconeogenesis. Gluconeogenesis from an evolutionary point of view is purely a last ditch effort to keep blood glucose levels high enough to support CNS activity. Ketogenic diets can trigger gluconeogenesis.