Modulation of temperature-induced tone by vasoconstrictor agents

Area of Science:

• Cardiovascular Physiology
• Vascular Smooth Muscle Biology
• Thermoregulation

Background:

• Hyperthermia triggers cardiovascular adjustments, including increased vascular resistance.
• Non-neural factors, like vascular tone, may also influence this response.
• Understanding vascular smooth muscle behavior during heating is crucial.

Purpose of the Study:

• To investigate alterations in vascular smooth muscle tone during heating to physiologically relevant temperatures (>37°C).
• To determine the role of extracellular calcium in hyperthermia-induced vascular contractions.

Main Methods:

• Vascular ring segments from rat mesenteric arteries and thoracic aortae were used.
• Temperature was gradually increased from 37°C to 43°C.
• Contractions were measured with and without prior constriction (phenylephrine or KCl) and in the presence of calcium channel blockers (nifedipine, diltiazem).

Main Results:

• Heating induced graded contractions in vascular rings, more pronounced with pre-existing tone.
• Hyperthermia-induced contractions were significantly attenuated by calcium channel antagonists.
• Vascular smooth muscle shows limited tension generation during heating without tone, but enhanced responses with agonist-induced tone.

Conclusions:

• Hyperthermia enhances vascular smooth muscle tension generation in the presence of agonist-induced tone.
• Extracellular calcium influx is critical for these enhanced contractile responses.
• Local regulation of vascular tone plays a role in hemodynamic adjustments to hyperthermia.