Abstract
The decrease of plasma insulin levels after physical training is explained mainly
by a decreased insulin secretion, but also to a significant degree by an increased
peripheral insulin metabolic clearance rate in several peripheral tissues and increased
insulin uptake in the liver. The peripheral tissues demonstrate an increased insulin
sensitivity, but this seems to be due to factors after the insulin receptor level.
An increased turnover of insulin at the receptor level might be postulated.
The explanation for the decrease of insulin secretion has been studied extensively.
A decreased Cortisol secretion might be a primary factor in physical training, followed
by lower insulin levels. Autonomic nervous system adaptations could also be involved
in the form of an increased α-adrenergic activity. Another alternative is that the
effect is mediated via an influence of physical training on a gut “incretin” factor,
facilitating insulin secretion. Finally, it might be considered that the increased
insulin sensitivity of muscle following physical training is regulating insulin secretion
via feedback mechanisms to the β cell. Recent demonstrations of inhibited glucose
uptake in the liver after exercise facilitates an explanation along these lines.
Key words
insulin secretion - insulin clearance - insulin receptor - α-receptor - β-receptor
- incretin - muscle - exercise
