Humoral factor(s) circulating in the blood of spontaneously hypertensive rats increases vascular tone and reduces constrictive responses of isolated rat caudal artery to stimulation of sympathetic fibers of the vascular wall

Abstract

It is shown that the perfusion pressure in isolated rat caudal artery rises and constrictive responses to electrical stimulation decrease when the blood of normotensive Wistar-Kyoto rats perfusing the vessel was replaced by the blood of spontaneously hypertensive rats. The norepinephrine release from the sympathetic terminals is reduced. Key Words: isolated vessel; humoral factors; electrical stimulation; norepinephrine release; spontaneously hypertensive ratsBoth pro-and antihypertensive humoral factors which are known to circulate in the blood of spontaneously hypertensive rats [3,4] are able to modulate the arterial pressure by affecting the tone and reactivity of vessels. However, the mechanism of action of many humoral factors remains unclear, since the effects of nervous and humoral factors on the cardiovascular system are hard to distinguish in the whole organism.A new method we proposed previously, namely perfusion of an isolated segment of rat caudal artery with blood from a conscious donor rat, allowed us to study the humoral factors circulating in the blood of spontaneously hypertensive rats (SHR) and their influence on the constrictive responses to stimulation of sympathetic fibers in the vascular wall. A modification of this method supplemented by measurement of the norepinephrine (NE) release from presynaptic terminals of sympathetic fibers has en- MATERIALS AND METHODSThe experiments were carried out on 6-7-monthold normotensive Wistar-Kyoto rats (WKY) and SHR weighing 250-350 g. The animals were used as blood donors. To this end the rats were narcotized with Nembutal (40 mg/kg, intraperitoneally), and the carotid and femoral arteries and the femoral vein were catheterized. In the course of the experiment blood for perfusion of the isolated caudal artery was drawn by means of a roll pump through the catheter introduced in the carotid artery and returned to the donor through the catheter introduced in the femoral vein, and the arterial pressure and heart rate in the donor rats were recorded using the catheter implanted in the femoral artery. The animals were conscious and moved freely in the cage throughout the experiment.The isolated segments of the caudal artery were obtained from decapitated WKY. The segment