Clamping Skeletal Muscle PO 2 Eliminates Hyperinsulinemic Microvascular Blood Flow Response

• Published in: The FASEB journal 2022-05, Vol.36 Suppl 1 (S1)
• Main Authors: Wells, Brenda N, Russell McEvoy, Gaylene M, Shogan, Hamza, Kiley, Meghan E, Fraser, Graham M
• Format: Article
• Language: English
• ISSN: 0892-6638; 1530-6860
• DOI: 10.1096/fasebj.2022.36.S1.R4499

To determine if insulin mediated hyperemia is partially dependent on local muscle oxygen concentration. The blood flow responses to insulin are partially mediated by the local metabolic demand reflecting the increased oxygen consumption required to uptake and convert glucose into glycogen in skeletal muscle. 16 male Sprague Dawley rats (161g - 204g) were anesthetized with sodium pentobarbital, the carotid artery and jugular vein were then cannulated for blood pressure monitoring and fluid resuscitation. Following cannulation, the extensor digitorum longus (EDL) was isolated and reflected onto an inverted microscope. Intravital video microscopy sequences of the EDL microcirculation were recorded during baseline and following hyperinsulinemic euglycemia or sham in all experiments. The muscle was reflected over a glass stage insert during Experiment 1a and 1b which allowed for direct observation of microvascular blood flow response to systemic insulin infusion in Experiment 1a. Experiment 1b consisted of a sham hyperinsulinemic euglycemic clamp which involved infusing saline at similar rates as insulin and glucose in standard clamp procedures. In Experiment 2, the EDL was reflected over a gas exchange chamber and microvascular capillary blood flow was recorded during sequential changes (7%-12%-2%-7%) of oxygen concentration [O ] within the chamber during baseline and euglycemic conditions. The gas exchange chamber is fitted into the stage of an inverted microscope that interfaces directly with the EDL via a gas permeable polydimethylsiloxane membrane. By adjusting the concentration of gases flowing through the gas exchange chamber we have direct control of the [O ] within the overlying muscle. Hemodynamic measurements including capillary red blood cell (RBC) velocity, supply rate (SR), hematocrit, and oxygen saturation (SO ) were taken from in focus capillaries in the EDL during each experiment and analyzed offline using custom MATLAB software. All animal protocols were approved by Memorial University's Institutional Animal Care Committee. In Experiment 1a, the hyperinsulinemic euglycemic clamp caused a significant increase in SR from 8.9 ± 3.1 to 14.2 ± 4.9 cells/s at baseline to euglycemia (p = 0.01; N = 6, 677 capillaries at baseline and 552 at clamp), while no significant SR variation was detected after performing a sham clamp in Experiment 1b (11.0 ± 1.6 cells/sec at baseline and 11.4 ± 3.7 cells/sec at sham clamp; N = 6, 837 capillaries at baseline and