Studies on left ventricular receptors, signalling in non-medullated vagal afferents.

Left ventricular receptors, signalling in non-medullated vagal fibres and displaying a low, irregular spontaneous activity, have been analysed by recordings of impulse activity in cardiac afferent nerves. The receptors were distributed diffusely all over the ventricle and in both superficial and deep layers of the myocardium. They were activated by occlusions of the ascending aorta, by substantial elevations of arterial blood pressure and by rapid infusions of saline or dextran, whenever these procedures produced a clearcut increase of intraventricular diastolic pressure and end-diastolic volume. The endings were also excited by veratrum alkaloids, nicotine and digitalis alkaloids. When activated, the receptors usually displayed a cardiac rhytm, but with intense stimulation the activity usually became continuous. The receptors evidently function as mechano- or deformation receptors, responding primarily to a distension of the ventricle. Activation of the receptors causes a reflex bradycardia and, in all probability, vasodilatation and blood pressure fall. They may contribute to the homeostatic control of blood pressure and blood volume, but their main function seems to be to protect the heart from e.g. imminent overloading. The endings are probably of main importance for the emergence of the Bezold-Jarisch reflex.