Vascular effects of the carotid baroreceptor reflex upon increased tissue osmolarity

Acute experiments were carried out on the vascular bed of cat hind leg upon perfusion at constant blood flow and increased tissue osmolarity through intraarterial hypertonic infusion. The activity of the carotid baroreceptors was changed by means of bilateral carotid fusion. The activity of the carotid baroreceptors was changed by means of bilateral carotid occlusion and by increasing or decreasing the carotid blood flow. Hyperosmolarity reduced both the increase in the vascular contraction in response to the decreased baroreceptor activity and the decrease of the contraction resulting from the increased baroreceptor activation. The smaller rise in the contraction was connected with the direct hyperosmolarity inhibition of vascular contractility. The smaller decrease in the vascular response was connected with the smaller initial contraction of the vascular muscle due to hyperosmolarity inhibition of the spontaneous contractile activity. The results presented show that upon increasing tissue osmolarity the resistance vessels manifest the same behaviour with respect to the changes in the activity of the carotid baroreceptors as in the case of muscle exercises. This supports the assumption of the possible participation of the decrease in the neurogenic vascular tone in the appearance of hyperosmolarity vasodilation and of exercise hyperemia.