Graded occlusion of perfused rat muscle vasculature decreases insulin action
Georgie C Vollus1, Eloise A Bradley, Merren K Roberts
1Department of Biochemistry, University of Tasmania Medical School, Private Bag 58, 7001, Hobart, Tasmania, Australia.
Abstract:
Insulin increases capillary recruitment in vivo and impairment of this may contribute to muscle insulin resistance by limiting either insulin or glucose delivery. In the present study, the effect of progressively decreased rat muscle perfusion on insulin action using graded occlusion with MS (microspheres; 15 mum in diameter) was examined. EC (energy charge), PCr/Cr (phosphocreatine/creatine ratio), AMPK (AMP-activated protein kinase) phosphorylation on Thr(172) (P-AMPKalpha/total AMPK), oxygen uptake, nutritive capacity, 2-deoxyglucose uptake, Akt phosphorylation on Ser(473) (P-Akt/total Akt) and muscle 2-deoxyglucose uptake were determined. Arterial injection of MS (0, 9, 15 and 30 x 10(6) MS/15 g of hindlimb muscle, as a bolus) into the pump-perfused (0.5 ml x min(-1) x g(-1) of wet weight) rat hindlimb led to increased pressure (-0.5+/-0.8, 15.9+/-2.1, 28.7+/-4.6 and 60.3+/-9.4 mmHg respectively) with minimal changes in oxygen uptake. Nutritive capacity was decreased from 10.6+/-1.0 to 3.8+/-0.9 micromol x g(-1) of muscle x h(-1) (P<0.05) with 30 x 10(6) MS. EC was unchanged, but PCr/Cr was decreased dose-dependently to 61% of basal with 30 x 10(6) MS. Insulin-mediated increases in P-Akt/total Akt decreased from 2.15+/-0.35 to 1.41+/-0.23 (P<0.05) and muscle 2-deoxyglucose uptake decreased from 130+/-19 to 80+/-12 microg x min(-1) x g(-1) of dry weight (P<0.05) with 15 x 10(6) MS; basal P-AMPKalpha in the absence of insulin was increased, but basal P-Akt/total Akt and muscle 2-deoxyglucose uptake were unaffected. In conclusion, partial occlusion of the hindlimb muscle has no effect on basal glucose uptake and marginally impacts on oxygen uptake, but markedly impairs insulin delivery to muscle and, thus, insulin-mediated Akt phosphorylation and glucose uptake.
Insights
Reduced blood flow in muscles impairs insulin
Area of Science:
- Physiology
- Metabolism
- Endocrinology
Background:
- Insulin enhances capillary recruitment, crucial for muscle insulin sensitivity.
- Impaired insulin or glucose delivery to muscles can lead to insulin resistance.
Purpose of the Study:
- To investigate how reduced muscle perfusion affects insulin action.
- To examine the impact of graded hindlimb muscle occlusion on insulin signaling and glucose uptake in rats.
Main Methods:
- Graded occlusion of rat hindlimb muscle perfusion using microspheres (MS).
- Measurement of energy charge (EC), phosphocreatine/creatine ratio (PCr/Cr), oxygen uptake, and nutritive capacity.
- Assessment of Akt phosphorylation (P-Akt/total Akt) and 2-deoxyglucose uptake in response to insulin.
Main Results:
- Microsphere-induced occlusion increased perfusion pressure but minimally affected oxygen uptake.
- Nutritive capacity and PCr/Cr ratio decreased with increasing microsphere dosage.
- Insulin-mediated Akt phosphorylation and 2-deoxyglucose uptake were significantly reduced with partial muscle occlusion.
Conclusions:
- Partial occlusion of hindlimb muscle impairs insulin delivery.
- This impairment significantly reduces insulin-mediated Akt phosphorylation and glucose uptake.
- Reduced muscle perfusion, not oxygen availability, is a key factor in muscle insulin resistance.
