Cooling-Induced Carotid Artery Dilatation

Abstract

Background and Purpose-Clinical and experimental studies seem to indicate that hypothermia may improve outcome in stroke victims and reduce experimental brain injury. The current interpretation is that cooling has a neuroprotective effect by reducing brain metabolism. The objective of our study was to test the hypothesis that hypothermia induces arterial vasodilatation and thereby increases cerebral blood flow. Methods-We recorded isometric tension in rabbit carotid artery strips in organ baths during stepwise cooling. The cooling responses were tested at basal tone, in noradrenaline-precontracted vessels, and after electric field stimulation. Results-Stepwise cooling from 37°C to 4°C induced reproducible graded relaxation, inversely proportional to temperature. The responses could be elicited at basal tone and in precontracted vessels. Cooling decreased the contractile responses to norepinephrine and potassium chloride. Cooling at 20°C decreased the contractile responses to electric field stimulation, while at 10°C these were totally abolished. Cooling-induced vasodilatation is not dependent on an endothelial mechanism. Key Words: carotid arteries Ⅲ hypothermia Ⅲ ischemia Ⅲ neuroprotection Ⅲ stroke W e previously studied thermal responses of smooth muscle in various species and organs of the body and found that the degree of active tension is very temperature dependent. Moreover, we detected marked regional differences in the cooling-response pattern in superficial and deep blood vessels, trachea, bronchi, urinary bladder detrusor muscle, and gut. Cutaneous veins contract, whereas deep extremity vessels dilate. 1 The aorta and pulmonary artery clearly show a cooling-induced relaxation, 2 whereas airways, 3 urinary bladder, 4 and gut contract. 5 As a treatment, hypothermia has been advocated as a potent modality in protecting neurons against lethal ischemic stress. In animal experiments, intraischemic hypothermia has been shown to be neuroprotective in global 6 and focal 7-9 cerebral ischemia and even when hypothermia is initiated after temporary cerebral ischemia. 10 Kuluz et al 11 found that selective brain cooling increases cortical cerebral blood flow. Conclusions-CoolingIt has been claimed that mild hypothermia is possibly the single most effective method of cerebroprotection developed to date. 12 Krieger et al 13 recently reported that hypothermia is effective in patients with acute brain infarction, demonstrating that hypothermia appears feasible and safe in cases of acute ischemic stroke even after thrombolysis. However, many questions regarding hypothermia remain to be addressed, and recently some clinical studies have questioned the effectiveness of hypothermia for traumatic brain injury. 14 In view of these considerations and the positive reports about hypothermia treatment in stroke victims, 15 we decided to extend our studies to include the carotid artery to test the hypothesis of a cooling-induced vasodilatation of brain supply vessels. Materials and MethodsAll procedures followed were within insti...

Selective Brain Cooling with Endovascular Intracarotid Infusion of Cold Saline: A Pilot Feasibility Study

“…Studies on ex vivo specimens from ICAs of animals and MCAs from human autopsies revealed vascular relaxation during cold exposure. 42,43 Relaxation of the MCA during TCD insonation would result in a decrease in MCA FV, which we observed in this study. A concurrent increase in peripheral vascular resistance (increase in PI) suggests that there was constriction of arterioles and precapillaries.…”

Transient Receptor Potential Channel Opening Releases Endogenous Acetylcholine, which Contributes to Endothelium-Dependent Relaxation Induced by Mild Hypothermia in Spontaneously Hypertensive Rat but Not Wistar-Kyoto Rat Arteries

“…Thus, the aorta, which is minimally or not at all innervated (Nilsson et al, 1986), was used in the experiments to exclude the possible involvement of neuronal acetylcholine released from surrounding nerve endings. In rabbit carotid arteries (Mustafa and Thulesius, 2002) or Sprague-Dawley rat pulmonary arteries and aortae (Mustafa and Thulesius, 2001), cooling induced direct relaxations that were not dependent on the presence of the endothelium and the release of NO or neurotransmitters. By contrast, the present study demonstrates that hypothermia (from 37 to 20°C) induces relaxation of both the SHR and WKY rat aorta, and the comparison of the findings in rings with and without endothelium permits the conclusion that the response is mainly dependent on the endothelium in the temperature range from 37 to 31°C, while it is due to a direct effect on the smooth muscle cells when the temperature decreases below 31°C.…”

Uncomplicated Rapid Posthypothermic Rewarming Alters Cerebrovascular Responsiveness

“…10,11 In contrast, vasoconstriction in response to hypothermia at 30°C has been reported 12 ; however, in that study the space under the window underwent continuous perfusion with artificial CSF, washing out endogenous vasoactive factors. Recently, Mustafa and Thulesius, 13 who reported cooling-induced carotid artery dilation, speculated that local carotid cooling may have therapeutic potential by increasing the brain's blood supply. Cerebral vasorelaxation on cooling may lead to a loss of resting tone.…”