TWO TYPES OF CORONARY VASOMOTOR REFLEXES

¹ Institute of Physiology, Medical University of Debrecen, Hungary

There are two receptor zones in the area of the coronary system. The reflex elicitable from the coronary sinus by stretching its wall serves to set blood pressure to a new level, whereas the coronary depressor reflex is similar in its properties to the simple depressor reflexes and as such serves to maintain blood pressure at a given level. The receptors of the latter reflex are located elsewhere in the left coronary bed, but not in the coronary sinus.

The coronary sinus reflex is characterized by its all-or-nothing nature: wall-stretching over the threshold does not further modify the reaction.

In contrast with this, the size of the coronary depressor response is proportionate to the increase of pressure.

Another feature in which coronary sinus reflex differs from the coronary depressor reflex is its trigger-like function; i.e. the reaction, once elicited, may persist even after the stimulus applied is no longer active.

In spite of the differences in their properties, the two reflexes form a functional unit, insofar as the coronary depressor reflex is capable of modulating the effect of the coronary sinus reflex.

On the basis of the experimental evidence, one branch of the left thoracic vagus may be assumed to play a specific role in the elicitation of these reflexes.