Daily voluntary exercise alters the cardiovascular response to hemorrhage in conscious male rats

By: Joslyn K. Ahlgren, Linda F. Hayward (Autonomic Neuroscience: Basic and Clinical 160 (2011) 42–52)

Blood loss is described by the response called hemorrhage (HEM). The first phase is called the "compensatory" phase, which consists of an increased heart rate (HR) and sympathetic activity. This is maintained until blood loss reaches 15-20% of total blood volume (TBV). Once blood volume drops past the critical point, the body goes into the "decompensatory" phase, where there is a decline in HR and AP. This will lead to increased levels of renin, vasopressin, and epinephrine. This leads to the "recovery" phase where sympathetic tone is restored. The longer the body is exposed to a hemorrhage, the harder the chance of recovery becomes.

Exercise has been shown to contribute to the cardiovascular system. Chronic exercise has been associated with enhanced health outcomes. It also affects areas of the brain that control AP and HR. These same regions of the brain have also been seen to contribute to the autonomic functions during HEM. The hypothesis was that exercise rats would display a change in autonomic responses to severe HEM. More specifically, he compensatory would be altered slightly, but the decompensatory phase would be significantly altered.

36 male rats were pair housed for 6 weeks in active (running wheel) or sedentary (no running) wheel conditions. The rats were at rest for 30-60 min where AP, MAP, and HR were recorded. Rats were then subjected to either a 30% TBV HEM over 15 min, sit quietly, or underwent baroreflex testing.

The results showed that following HEM, HR and MAP declined in both groups, but overall, SED animals had a greater drop in MAP and HR in response to HEM, than active animals. HR was also significantly lower in SEDs. Also, the HRV analysis revealed putative alterations in EX vs. SED .The results support previous reports of daily exercise modifying neuronal excitability.

When blood loss initially occurs, baroreflex adjustments occur to compensate for this loss. This study showed that during this phase, exercise significantly augmented the baroreflex increases in HR in response to the drop in AP. During the decompensatory phase, MAP was significantly higher at the end of HEM in exercise animals. At 60 min, post HEM, HR was significantly higher in EX. This shows that EX does indeed affect the recovery phase and can help increase survival rates. The results in the study also support that exercise training improves the cardiovascular activity during hypotensive periods.

This study relates to our lab by focusing on how exercise affects the body as well as the brains ability to recover from a hemorrhage. The SNS is vital to this process and contributes to the animals overall health. I would like to see how the RVLM specifically changes during times of blood loss. I would predict that it would fire at a greater rate once barorelex receptors sense blood volume decrease.


-Tsetse Fly