Exercise and cardiac performance capacity in rats with partial sympathectomy

Area of Science:

• Cardiovascular Physiology
• Exercise Physiology
• Sympathetic Nervous System

Background:

• The sympathetic nervous system plays a crucial role in regulating cardiovascular function during exercise.
• Understanding the impact of sympathectomy on exercise capacity is vital for comprehending cardiovascular control mechanisms.

Purpose of the Study:

• To investigate the effects of partial sympathectomy (SYMX) on maximal oxygen uptake (VO2 max), heart rate (HR), cardiac contractile capacity, and myofibril ATPase activity in rats.
• To compare exercise responses between normal control (NC) rats and SYMX rats, and to assess the role of beta-1 blockade in NC rats.

Main Methods:

• Partial sympathectomy was induced in rats using chronic guanethidine injections.
• Maximal oxygen uptake (VO2 max) and heart rate (HR) were measured during exercise.
• Cardiac contractile capacity was assessed in situ.
• Ca2+ regulation of cardiac myofibril ATPase activity was analyzed.
• Normal rats were studied with and without atenolol (a beta-1 blocker).

Main Results:

• SYMX did not alter Ca2+-regulated cardiac myofibril ATPase activity.
• Cardiac functional capacity (left ventricular pressure, +dP/dtmax) was similar between NC and SYMX groups under stress.
• Exercise VO2 max was 15% lower in SYMX rats compared to NC rats (P < 0.05).
• This VO2 max reduction in SYMX rats correlated with a decrease in maximal heart rate (HRmax).
• Normal rats with beta-blockade achieved normal VO2 max despite lower HRmax than SYMX rats.

Conclusions:

• Partial sympathectomy reduces exercise VO2 max and HRmax in rats.
• Despite reduced HRmax, beta-blockade in normal rats allowed for normal VO2 max attainment.
• These findings suggest that attenuated heart rate and contractility may enhance the capacity to maintain VO2 max during acute exercise compared to chemical sympathectomy.