Circulatory Control via Vagal Afferents: IV. Integration of the central control mechanisms in the circulatory-adaptation to variations of blood volume

The interrelations of receptor mechanisms localized to the central part of the cardiovascular system have been studied by alternative exclusion of afferent discharges via the laryngeal pathway, vagus trunk and sinus nerve in Sprague-Dawley rats. An initial increase of arterial pressure followed by a lasting decrease, usually coincident with the appearance of pressure waves, was found in most animals on laryngeal deafferentation but in others on vagotomy. A preceding or subsequent exclusion of afferents via, respectively, the vagus trunk and laryngeal nerves exerted no or only small effects. The pressure response to occlusion of the common carotid arteries was decreased after blood infusions, also after hemorrhage to 60 mm Hg. On a further blood loss to a level of 25 mm Hg the response increased. Occlusion exclusively of the internal carotids provoked practically the same effect under these conditions. On laryngeal deafferentation and vagotomy, respectively, the pressure response increased. Deafferentation after blood infusion, especially combined with carotid occlusion and vagotomy, provoked forced respiration and in 3 of 6 animals signs of pulmonary edema, fatal in two. It was concluded that in hypervolemia the circulation is adapted wholly and in hypovolemia in part via afferents running in the laryngeal communicans and/or vagus trunk.