ONTOGENY OF CARDIAC RATE REGULATION AND BROWN FAT THERMOGENESIS IN GOLDEN-HAMSTERS (MESOCRICETUS-AURATUS)

It was shown previously in infant rats (Rattus norvegicus) that the ab ility to produce heat in the cold using brown adipose tissue (BAT) is closely related to the ability to maintain cardiac rate. When the limi ts of BAT thermogenesis were exceeded, interscapular temperature (whic h reflects the temperature of the interscapular BAT depot) and cardiac rate fell together. As an extension of this earlier study. the relati on between BAT thermogenesis and cardiac rate was examined here in the golden hamster (Mesocricetus auratus), a species whose young do not e xhibit BAT thermogenesis until the end of the 2nd week postpartum. It was found that 3 to 12-day-old hamsters were unable to increase shiver ing or nonshivering thermogenesis in the cold and exhibited decreases in cardiac rate that proceeded in lock-step with decreases in intersca pular temperature. In contrast, as the thermogenic capability of hamst ers increased after 12 days of age, cardiac rate was maintained within narrow limits across a wide range of air temperatures. These results support the hypothesis that heat produced by BAT helps to warm the hea rt and thus aids in the maintenance of cardiac rate during cold exposu re.