Differences in brown adipose tissue thermogenic responses between Long-Evans and Sprague-Dawley rats.

Temperature experiments of 4- and 21 degrees C-acclimated conscious and anesthetized Sprague-Dawley (SD) and Long-Evans (LE) rats revealed that the LE groups or SD rats acclimated to 4 degrees C had significant increases in intracapsular brown adipose tissue (IBAT) temperature above core after ventromedial hypothalamic nucleus (VMH) electrical stimulation or after norepinephrine (NE) infusion (50 micrograms/kg total dose), whereas IBAT temperatures of SD rats (acclimated to 21 degrees C) rose only after intravenous NE. Another study of 21- or 4 degrees C-acclimated SD rats revealed that only the 4 degrees C-acclimated group showed graded increases in IBAT temperature after VMH electrical stimulation as current amplitude or total current duration (not pulse frequency) of the electrical stimulus was increased. In vitro analysis of isolated IBAT tissues of age-matched anesthetized LE or SD rats acclimated to 21 degrees C showed that many indicators of thermogenic capacity including mitochondrial uncoupling protein were significantly lower in the SD group. The results demonstrate that lean male SD rats acclimated to 21 degrees C have suppressed IBAT temperature responses to VMH electrical stimulation compared with lean LE rats due to a reduced thermogenic capacity of that tissue.