Effect of hypothermia on baroreflex control of heart rate and renal sympathetic nerve activity in anaesthetized rats

摘要: The present study investigated the effect of acute hypothermia on baroreflex control heart rate (HR) and renal sympathetic nerve activity (RSNA) by generating logistic function curves, using bolus doses phenylephrine sodium nitroprusside, in anaesthetized male Wistar rats at a core temperature (T(b)) 37 degrees C, during severe T(b)= 25 C rewarming to C. Comparisons were made between without (euthermic, n= 6) with (acclimated, 7) prior exposure lower ambient temperatures shorter photoperiod, simulating adaptation winter conditions. In both groups rats, shifted baroreflex-RSNA curve slightly leftwards downwards decreases setpoint pressure maximal gain, whereas it markedly impaired baroreflex-HR characterized response range approximately 90% (P < 0.001), minimum 10% 0.05) maximum gain 95% from that All parameters restored precooling levels rewarming. Electrical stimulation cardiac vagal efferents induced voltage-related bradycardia, magnitude which was partially reduced hypothermia, there significant prolongation electrocardiogram intervals indicating delay conduction. Mild suppression RSNA could contribute hypothermic hypotension may primarily reflect an T(b) central drive. marked attenuation HR likely be due impairment peripheral components reflex arc. Baroreflex similar implied non-adaptive chronic cold exposure.