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IN VITRO ANGIOGENESIS INCREASES WITH CHRONIC PASSIVE HEAT THERAPY: LIKELY MECHANISM FOR IMPROVED CARDIOVASCULAR HEALTH

Abstract

Chronic passive heat therapy (CHT) shows exciting potential for improving cardiovascular health and overall quality of life. Angiogenesis occurs naturally when endothelial cells lining the inside of blood vessels proliferate and reorganize into new vasculature. Heat stress induces expression of many factors that promote angiogenesis which can decrease blood pressure. CHT may therefore be an effective means of increasing vascularization and improving vascular health. Angiogenesis can be assessed easily and non-invasively by using an in vitro endothelial tubule formation bioassay. PURPOSE: To determine if acute heating and/or chronic passive heating has a positive effect on in vitro endothelial tubule formation. METHODS: Six sedentary, healthy individuals (aged 22±1 yrs) were subjected to 8 weeks of heating via hot tub (40.5°C) 4-5 times per week for 36 sessions. During each session, rectal temperature was increased and maintained at ≥38.5°C for 60 minutes. Blood samples were collected into serum separating vacutainers before and after each heating session at weeks 0 and 8. Two in vitro angiogenesis bioassays were performed for each sample by plating cultured human umbilical vein endothelial cells (HUVECs) onto Matrigel and treating with serum from subjects. After 10 hours of incubation, tubule formation per frame was determined using phase-contrast microscopy at 2.5X magnification by two blinded experimenters using ImageJ software and results were averaged. RESULTS: Total tubule length increased after 8 weeks of CHT from 71.7±1.4 to 75.5±1.6 mm/frame (p=0.02), and tended to increase with acute heating to 74.2±1.5 mm/frame (p=0.19). CONCLUSION: Heat therapy increases the capacity for angiogenesis both acutely (single heat exposure) and chronically, suggesting CHT improves vascular health. CHT is simple enough to be used by many patient populations with little or no supervision and may be an effective means of improving cardiovascular health and therefore quality of life.

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