Effects of propranolol on cardiopulmonary function in the pony during submaximal exercise.

This study examines how propranolol, a beta-adrenergic receptor blocker, affects the heart and lung functions of ponies during exercise. The study finds that while the drug doesn’t affect resting ponies, it does reduce their heart function and increases their body temperature during heightened physical activity.

Experimental Design and Implementation

The research was conducted on four ponies, with standard exercise tests (SET) administered to study their cardiopulmonary responses. The exercise tests:

• Involved four 5-minute, sequentially faster running sessions on a treadmill, with speeds ranging from 1.0 to 2.8 m/sec and a 7 degrees incline.
• Included monitoring and recording data when the ponies were at rest, during exercise, and during recovery.

Propranolol Administration and its Impact

Propranolol, a drug that blocks beta-adrenergic receptors (part of the nervous system that prepares the body for physical activity), was administered to the ponies. Its effects:

• Did not change cardiopulmonary function when given to ponies at rest.
• During exercise, the drug suppressed the increase in heart rate, pulmonary artery flow (indicating decreased cardiac output), and right ventricular dP/dt (a measure of muscular contraction in the heart).
• Propranolol administration did result in notably higher body temperatures and increased pressures in the pulmonary artery and right ventricle.

Parameters Unaffected by Propranolol

Several physiological parameters were unresponsive to propranolol treatment:

• The drug had no influence on the mean arterial pressure, levels of haemoglobin and haematocrit (indicators of oxygen-carrying capacity), arterial blood gases and pH, and blood lactate (a product of high-intensity exercise).

Conclusion

Based on these observations, the researchers concluded that there is no sympathetic activity – part of the nervous system that kicks into action during “fight or flight” situations – acting on the ponies’ hearts when they are at rest. During exercise, however, the researchers suggest that the ponies’ lungs are dilating owing to the activity of beta-adrenergic receptors. This dilation is reportedly reduced by the administered propranolol.