Leucine reduces the duration of insulin-induced PI 3-kinase activity in rat skeletal muscle.
Level 5 - mechanism / opinion, no new human data
Animal physiological and molecular study
PubMed 15339747 · doi:10.1152/ajpendo.00272.2004
What was done
Fasted rats (~200 g, 12 h fast) were administered oral doses of carbohydrate (1.31 g glucose, 1.31 g sucrose), leucine (270 mg), or carbohydrate plus leucine. Rats were killed at 15, 30, 60, and 90 min after treatment. Plasma and gastrocnemius muscles were collected to measure PI 3-kinase activity, glucose uptake, and the release of translation initiation factor eIF4E from 4E-BP1. Sample size is not reported in the abstract.
What was found
Carbohydrate alone stimulated PI 3-kinase activity and glucose uptake with no effect on eIF4E. Leucine alone stimulated eIF4E release from 4E-BP1 without altering PI 3-kinase activity or glucose uptake. Carbohydrate plus leucine reduced the magnitude and duration of the PI 3-kinase response, while maintaining glucose uptake similar to carbohydrate alone and eIF4E levels similar to leucine alone. The abstract reports directional changes without numerical values or confidence intervals.
Why it matters
The study shows that leucine can negatively modulate upstream insulin signaling via PI 3-kinase in skeletal muscle without compromising acute glucose transport.
Limits
Findings from an acute bolus in rodents may not reflect human metabolic responses or long-term dietary patterns. The abstract omits sample sizes, quantitative values, and variance metrics.
Cited by
- context A single dose of insulin activates mTOR for up to 24 hours, whereas leucine only activates mTOR for approximately one to two hours.