Absence of Vasoconstrictor Substance in Blood of Rats with Renal Hypertension

Abstract

Using an adaptation of Griffith's and Collins' method for measuring systolic pressure 1 in rats which had developed hypertension as a result of renal insufficiency, 2 we have studied the effect of destroying the central nervous system on the blood pressure of normal and of hypertensive rats. The blood pressure was determined under light ether anesthesia, and then, after inserting a tracheal cannula connected with a device for arterial respiration, the rat was pithed and decerebrated. A cord, passed around the neck under the skin and trachea, was drawn tight crushing the cervical spine and ligating the carotid and vertebral vessels. Through a thoracic laminectomy a wire with a beaded tip was passed up and down the spinal canal. In this way the central nervous system can be destroyed quickly and with little blood-loss, and the preparation, without artificial warming, will last for 5 hours. The blood pressure remains constant during the first half hour, falling slowly thereafter. We followed the pressure during the period from 2 to 30 min. after pithing and decerebration in 10 normal and in 10 hypertensive male rats. The control level in the former was 117.6 mm. Hg average, varying from 85 to 136 mm.; in the latter the preoperative range was 151 to 209 mm., average 176.4 mm. After destroying the central nervous system the average level in the normals was 55.3 mm. Hg., range 42 to 66 mm., while the hypertensive group averaged 54.5 mm., range 45 to 66 mm. In the animals with destruction of the nervous system epinephrine and pituitrin, given intraperitoneally, caused a marked but transient rise in pressure. We therefore conclude that whatever pressor substance may be present in the plasma of rats with renal hypertension has no vasoconstrictor effect but acts through the vasomotor center.