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Vascular reactivity and baroreflex function during hyperthermia in conscious rats
M P Massett1, S J Lewis, H M Stauss
1Department of Exercise Science, The University of Iowa, Iowa City, Iowa 52242, USA.
Summary
Hyperthermia alters cardiovascular responses to vasoactive agents. While hemodynamic effects are blunted, sympathetic neural activity is augmented, impacting baroreflex control differently for heart rate and nerve activity.
Area of Science:
- Cardiovascular Physiology
- Autonomic Nervous System Regulation
- Thermoregulation
Background:
- Hemodynamic responses to vasoconstrictors are blunted during heating.
- The impact of hyperthermia on reflex neural responses to vasoactive agents remains unclear.
Purpose of the Study:
- To investigate the effects of hyperthermia on hemodynamic and baroreflex-mediated sympathetic neural responses to vasoactive agents.
- To compare these responses in conscious, unrestrained rats under normothermic and hyperthermic conditions.
Main Methods:
- Measured splanchnic sympathetic nerve activity (SpNA) and systemic/regional hemodynamics.
- Administered phenylephrine and sodium nitroprusside during normothermia (37°C) and hyperthermia (41.5°C).
- Analyzed baroreflex curves relating heart rate (HR) and SpNA to mean arterial blood pressure (BP).
Main Results:
- Hemodynamic responses to phenylephrine and sodium nitroprusside were blunted during hyperthermia.
- SpNA responses to both agents were augmented or unchanged during heating.
- Baroreflex curves shifted rightward at 41.5°C, reducing BP-HR reflex range/gain but augmenting BP-SpNA reflex range.
Conclusions:
- Hyperthermia alters in vivo cardiovascular and sympathetic neural responses to vasoactive agents.
- Heating differentially affects arterial baroreflex control of HR and SpNA.
- Hyperthermia shifts baroreflex curves toward higher BP but selectively attenuates HR control.