Reflex and neuro-humoral pressor action of the hypertonic solutions.

The intraarterial injections of 50% urea or 20% NaCl induced a rise of the systemic arterial blood pressure simultaneously with a constriction of the vessels of the legs. The mechanism which is responsible for these phenomena is very complex. It includes a reflex arising from the arterial wall, which is mediated through the spinal cord, the release of catecholamines and of some still nonidentified pressor substances and a central component which is normally masked by the depressor sinus reflex.