We previously demonstrated greater age-related loss of cold-exposed thermoregulatory ability and brown adipose tissue (BAT) thermogenic capacity in male than in female F344 rats. BAT in older males is significantly diminished in mass and less responsive to cold stimulation in vivo despite a stronger sympathetic drive than in females. This investigation tested the hypothesis that the respiratory capacity of individual brown adipocytes is less in older males than in older females and younger males. Brown adipocytes were isolated from male and female F344 rats at 6. 12, and 26 mo of age, and oxygen consumption was measured polarigraphically in response to various concentrations of norepinephrme (NE) and CL 316,243 (a specific β3-agonist). All 26 mo rats maintained stable body weights for three months prior to sacrifice. Interscapular BAT weight (mg BAT/g body weight) was greater in females than in males at 12 and 26 mo, with no difference observed at 6 mo (females: 6 mo = 0.66 ±0.03, 12 mo = 0.82 ±0.14, 26 mo = 087 ± 0.05, males S mo- 0.60± 0.05, 12 mo = 0 55 ±0.03, 26 mo = 0.51 ±0.05). In isolated brown adipocytes, there were no significant aging/gender differences in maximal rates of respiration measured in response to either NE or CL 316,243 Maximal responses to NE (nmol Oj/min/IO6 cells) were: females: 6 mo = 666 ±24, 12 mo = 534 ±32, 26 mo = 579 ±26, males: 6 mo = 814 ±86, 12 mo = 745 ±31 26 mo = 689 ±44 Similarly, the concentration required to elicit half-maximal respiration in response to either agonist did not appear to differ significantly between groups. Our data indicate that the aging/gender differences observed in cold-induced BAT thermogenesis in vivo are most likely related to differences in the amount of brown fat rather than to differences in the response of individual cells.
|Original language||English (US)|
|State||Published - 1996|
ASJC Scopus subject areas
- Agricultural and Biological Sciences (miscellaneous)
- Biochemistry, Genetics and Molecular Biology(all)
- Cell Biology