The effects of temperature on isolated hearts from neonatal through post-weanling rats

Effects of low temperature on contraction in papillary muscles from rabbit, rat, and hedgehog

During hibernation the body temperature may fall to only a few degrees above 0 degree C. The heart of the hedgehog continues to function whereas the hearts of nonhibernating mammals stop beating. The present study was performed to investigate and compare the mechanical responses to hypothermia in rabbits, rats, and hedgehogs. Isometric force was recorded from papillary muscles mounted in an organ bath and effects of hypothermia on the mechanical restitution curve were also compared. A reduction of bath temperature from 35 degrees C caused an increase in peak developed force. Maximum force was seen at 20 degrees C in the rabbit, 15 degrees C in the rat, and 10 degrees C in the hedgehog preparations. In all the species there was a similar prolongation of time to peak force and of time from peak to half-relaxation as temperature was lowered. An increase in resting force and after-contractions were recorded in the rabbit and rat muscles at temperatures below 15 and 10 degrees C, respectively. The rabbit and rat preparations became inexcitable at temperatures below 10 and 5 degrees C, respectively. The hedgehog papillary muscle, on the other hand, still contracted at 0 degree C and did not show increased resting force nor after-contractions. The results are consistent with the hypothesis that there is a calcium overload in cardiac cells from rabbit and rat at low temperatures but there is no calcium overload in the hedgehog muscle during hypothermia.

The effect of temperature on isolated perfused hearts of heterothermic marsupials

1. The thermal response of isolated perfused hearts of four dasyurid marsupials was determined and compared with that of two rodents. 2. Heart beat rate was strongly temperature dependent in all species. 3. The temperature of cardiac arrest in the species investigated in the present study and of others collected from the literature occurred at a mean of about 13 degrees C in homeotherms, 7 degrees C in daily heterotherms, and 1 degrees C in hibernators. 4. For both marsupials and placentals the temperature of cardiac arrest in hibernators and daily heterotherms correlated with the minimum body temperature during torpor.