Supramaximal Intensity Hypoxic Exercise and Vascular Function Assessment in Mice

Summary

High-intensity training in hypoxia is a protocol that has been proven to induce vascular adaptations potentially beneficial in some patients and to improve athletes' repeated sprint ability. Here, we test the feasibility of training mice using that protocol and identify those vascular adaptations using ex vivo vascular function assessment.

Abstract

Exercise training is an important strategy for maintaining health and preventing many chronic diseases. It is the first line of treatment recommended by international guidelines for patients suffering from cardiovascular diseases, more specifically, lower extremity artery diseases, where the patients' walking capacity is considerably altered, affecting their quality of life.

Traditionally, both low continuous exercise and interval training have been used. Recently, supramaximal training has also been shown to improve athletes' performances via vascular adaptations, amongst other mechanisms. The combination of this type of training with hypoxia could bring an additional and/or synergic effect, which could be of interest for certain pathologies. Here, we describe how to perform supramaximal intensity training sessions in hypoxia on healthy mice at 150% of their maximal speed, using a motorized treadmill and a hypoxic box. We also show how to dissect the mouse in order to retrieve organs of interest, particularly the pulmonary artery, the abdominal aorta, and the iliac artery. Finally, we show how to perform ex vivo vascular function assessment on the retrieved vessels, using isometric tension studies.

Introduction

In hypoxia, the decreased inspired fraction of oxygen (O₂) leads to hypoxemia (lowered arterial pressure in hypoxia) and an altered O₂ transport capacity¹. Acute hypoxia induces an increased sympathetic vasoconstrictor activity directed toward skeletal muscle² and an opposed 'compensatory' vasodilatation.

At submaximal intensity in hypoxia, this 'compensatory' vasodilatation, relative to the same level of exercise under normoxic conditions, is well established³. This vasodilation is essential to ensure an augmented....

Protocol

The local state's animal care committee (Service de la Consommation et des Affaires Vétérinaires [SCAV], Lausanne, Switzerland) approved all experiments (authorization VD3224; 01.06.2017) and all experiments were carried out in accordance with the relevant guidelines and regulations.

1. Animal housing and Preparation

1. House 6 to 8 week-old C57BL/6J male mice in the animal facility for at least 1 week prior to the beginning of the experiments in order for the mice to get used to their new housing conditions. For practical reasons, mice of the same experimental group are usually housed together.
2. Keep the mic....

Results

To our knowledge, the present study is the first to describe a program of supramaximal intensity training in normoxia and in hypoxia for mice. In this protocol, mice ran four sets of five 10 s sprints with a 20 s recovery in between each sprint. The sets were interspersed with 5 min of recovery periods. It was unknown whether the mice would be capable of sustaining such a protocol and complete it properly. However, according to Figure 5, the body weight gain .......

Discussion

The first objective of this study was to assess the feasibility of hypoxic high-intensity training in mice and to determine the adequate characteristics of the protocol that would be well tolerated by mice. Purposely, since there is no data using supramaximal (i.e., more than V_max) intensity training in mice, we had to perform trials based on previous protocols developed with athletes, which consisted of four to five sets of five all-out sprints (about 200% of V_max), interspersed with 20 s active re.......

Materials

Name	Company	Catalog Number	Comments
Cotton swab	Q-tip
Gas mixer Sonimix 7100	LSI Swissgas, Geneva, Switzerland		Gas-flow: 10 L/min and 1 L/min for O2 and CO2, respectively
Hypoxic Box	Homemade		Made in Plexiglas
Motorized rodents treadmill Panlab LE-8710	Bioseb, France
Oximeter Greisinger GOX 100	GREISINGER electronic Gmbh, Regenstauf, Germany
Sedacom software	Bioseb, France
Strain gauge	PowerLab/8SP; ADInstruments