Skeletal muscle blood flow response to local PO2 is impaired in high fat diet fed Sprague Dawley and Zucker Diabetic Sprague Dawley rats
Authors: Russell McEvoy Gaylene , Wells Brenda , Kiley Meghan , Fraser Graham 
Published: May 2023

Objective: Quantify the capillary blood flow responses to dynamic changes in oxygen concentrations ([O2]) in 27-week-old Sprague Dawley (SD) and Zucker Diabetic Sprague Dawley (ZDSD) type 2 diabetic (T2D) rats during hyperinsulinemic-euglycemic clamp. Hypothesis: Chronic hyperglycemia and elevated insulin in T2D causes impaired oxygen mediated blood flow regulation leading to functional defects in capillary network blood flow distribution at rest, during hyperinsulinemia, and in response to oxygen challenges. Methods: 8 SD and 10 ZDSD rats were fed high fat (HF) diet upon arrival at 15 weeks old, transitioned to a HF and high sugar diet from 16-19 weeks old, to induce T2D in the ZDSD strain, before being returned to HF until intravital video microscopy (IVVM). At 27 weeks of age, animals were fasted overnight and on the morning of the experiment animals were anaesthetized, mechanically ventilated, and catheters were introduced for systemic monitoring, fluid resuscitation and anaesthetic administration. The extensor digitorum longus muscle was isolated, blunt dissected, and reflected over a microfluidic gas exchange chamber fitted in the stage of an inverted microscope. Microvascular blood flow responses to sequential changes in [O2] (7%-12%-2%-7%) were recorded at baseline and during hyperinsulinemic-euglycemic clamp. Hyperinsulinemic-euglycemic clamp was achieved by simultaneous infusion of insulin (2U/hr/kg) and variable rate of 50% glucose until euglycemia was reached (5-7 mM). ZDSD rats with fasting blood glucose <20 mM on the day of IVVM were excluded from the hyperglycemic group. Analysis of IVVM videos was completed offline using custom MATLAB software. Animal protocols were approved by Memorial University’s Animal Care Committee. Results: SD red blood cell (RBC) saturation (SO2) significantly increased in response to 12% [O2] at both baseline and clamp (62.0 ± 5.9 vs. 75.8 ± 3.8 %, p <0.0001, and 62.7 ± 8.2 vs. 76.7 ± 6.5 %, p = 0.0001), RBC SO2 significantly decreased with 2% [O2] under both conditions compared to 7% (62.0 ± 5.9 vs. 38.1 ± 6.3 %, p <0.0001, and 62.7 ± 8.2 vs. 46.0 ± 9.5 %, p <0.0001). RBC velocity, supply rate (SR) and hematocrit showed no change from 7% (174.8 ± 59.7 μm/s, 10.7 ± 3.4 cells/s, and 27.5 ± 3.8 %) in response to increased or decreased [O2]. ZDSD rats had a significant increase between baseline and clamp in RBC SR at 12% (19.5 ± 3.3 vs 23.7 ± 9.1 cells/s, p = 0.0151) as well as at 2% (14.9 ± 2.6 vs 23.9 ± 8.0 cells/s, p = 0.0295). However, there was no change in RBC velocity or hematocrit in the ZDSD strain in response to imposed [O2] changes at baseline and clamp. Conclusion: SD and ZDSD animals lacked expected responses in capillary RBC velocity, SR, and hematocrit to imposed local [O2] changes both at baseline and during euglycemic clamp. This finding suggests that both hyperglycemia in T2D and high fat feeding alone affects microvascular blood flow responses to acute changes in local oxygen concentrations. This project was supported by the Canadian Institute of Health Research through a project grant to GMF. Studentships were supported by Memorial University's School of Graduate Studies and the Faculty of Medicine. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.