Hyperthermia-induced vasoconstriction of the carotid artery, a possible causative factor of heatstroke

Abstract

Clinical and experimental studies indicate that hyperthermia can cause heatstroke with cerebral ischemia and brain damage. However, no study has examined the direct effects of heating carotid artery smooth muscle and tested the hypothesis that hyperthermia induces arterial vasoconstriction and, thereby, decreases cerebral blood flow. We recorded isometric tension of rabbit carotid artery strips in organ baths during stepwise temperature elevation. The heating responses were tested at basal tone, in norepinephrine- and KCl-precontracted vessels, and after electrical field stimulation. Stepwise heating from 37 degrees C to 47 degrees C induced reproducible graded contraction proportional to temperature. The responses could be elicited at basal tone and in precontracted vessels. Heating decreased the contractile responses to norepinephrine and electrical field stimulation but increased contraction to KCl. These responses were not eliminated by pretreatment with the neuronal blocker tetrodotoxin. Our results demonstrate that heating carotid artery preparations above 37 degrees C (normothermia) induced a reversible graded vasoconstriction proportional to temperature. In vivo this reaction may lead to a decrease in cerebral blood flow and cerebral ischemia with brain damage as in heatstroke. The heating-induced contraction is not mediated by a neurogenic process but is due to altered transcellular Ca2+ transport. Cooling, in particular of the neck area, therefore, should be used in the treatment of heatstroke.

Differential effect of hyperthermia on nerves and smooth muscle of the mouse ileum

“…Similar results were found with in vivo hyperthermia in dogs, where at a core temperature of 408C systemic vascular resistance significantly decreased [19]. Other studies on the arteries of various animals have shown that hyperthermia induced vasoconstriction [9,11,20]. It was postulated that this heating-induced contraction was mediated by the inhibition of K þ channels [20].…”

“…Other studies on the arteries of various animals have shown that hyperthermia induced vasoconstriction [9,11,20]. It was postulated that this heating-induced contraction was mediated by the inhibition of K þ channels [20]. The same study showed a decrease in contractility at high temperatures in response to norepinephrine and electrical field stimulation (EFS).…”

Cerebral Vascular Control and Metabolism in Heat Stress

“…Lastly, reductions in CBF during heat stress may also be influenced by direct influences of temperature on the vascular smooth muscle cells. For example, heating isolated carotid artery rings of the rabbit induce temperature-dependent vasoconstriction, explained by the inhibition of potassium channels (316). It remains unknown if similar vasogenic consequences of temperature itself are present in the intact vessel.…”

Local heating, but not indirect whole body heating, increases human skeletal muscle blood flow

“…This stimulus may also decrease the resistance of upstream feed arteries (1). Although in some ex vivo experiments heating relaxes isolated blood vessels, especially cutaneous veins (2), it is evident that in the majority of animal studies heating per se does not change or slightly increases the tone of (arterial) blood vessels, such as in mesenteric and carotid arteries (19,22). These latter observations are in line with the understanding that warm blood is shunted from the body's core to skin so that heat can more effectively be released, although clearly sympathetically mediated vasoconstriction is the primary driver of this response.…”