Effects of Adrenaline

Autonomic nerve fibres controlling the heart arise in the brain stem. Sympathetic fibres innervate all regions of the frog heart (sinus venosus, atria and ventricle), while parasympathetic fibres go to the sinus and atria but virtually none go to the ventricle. Stimulation of sympathetic fibres can be mimicked in the pithed frog by pipetting a few drops of Ringer's solution containing adrenaline (50 µg/ml) directly onto the heart. The adrenaline will act at the receptor sites on cardiac muscle cells in the same way as the neurotransmitter released by sympathetic nerves.

The record trace shows a normal heart beat followed by a trace recorded after dropwise application of adrenaline to the heart in the region of the sinus-venosus.

Task
You should measure the rate of contraction (number of beats per minute) before and after application of adrenaline until maximal effects are observed. At this point normal Ringer's is pipetted onto the heart and the heart is allowed to recover. Recovery can take several minutes.

Changes in the force of both atrial and ventricular contraction should also be observed.

Use the play/pause button to halt the display to enable you to take your measurements more easily.