Evaluation of neurogenic and humoral factors in blood pressure maintenance in normal and toxemic pregnancy using tetraethylammonium chloride.

Elevation of the arterial blood pressure is one of the most characteristic signs of toxemia of pregnancy. That this blood pressure elevation must reflect an increase in peripheral resistance in the toxemic patient is well recognized. More and more emphasis has been placed on the observation of vasoconstrictor phenomena in this illness so that arteriolar spasm is now thought to represent a frequent if not universal concomitant of toxemia. Since, however, it is well established that constrictor responses may be initiated through both neurogenic and humoral mechanisms, the question as to the primacy of either of these factors in the hypertension of toxemia remains unanswered. Designation of the specific hypertensive disease of pregnancy as toxemia implies a primary humoral disorder. Despite the lack of conclusive evidence to support this concept, it has gained wide acceptance. Investigators have been occupied with the search for hormones, pressor agents and enzyme inhibitors peculiar to gestation. Although significant discoveries have been made, none has clarified the nature of blood pressure control in either toxemia or normal pregnancy. The recent development of pharmacologic agents which induce transient paralysis of the autonomic nervous system has provided a valuable adjunct for study of the mechanisms involved in blood pressure control. Tetraethylammonium chloride (TEAC), by blocking sympathetic impulse transmission at the ganglionic level, abolishes neurogenic tone. Failure to obtain a fall in blood pressure following TEAC suggests the activity of humoral agents. After sympathetic block, the blood pressure remains responsive to pressor substances and thus must be maintained by humoral mechanisms together with intrinsic vascular tone. Accordingly, an assay of TEAC responses in normal and toxemic pregnancy was undertaken in an effort to throw light on the relative importance of humoral and neurogenic factors in blood pressure maintenance in these conditions.