Rapid but transient atrophy of brown adipose tissue in capsaicin-desensitized rats

Our previous studies showed atrophy of brown adipose tissue (BAT) in capsaicin-desensitized rats during the period 11-28 days after injections [Cui et al., Am. J. Physiol. 259 (Regulatory Integrative Comp. Physiol. 28): R324-R332, 1990]. The objective of the present studies was to assess the rapidity with which the atrophy occurred and the extent to which recovery had occurred by 8 wk. Rats, either vehicle-injected controls or capsaicin injected, were studied 1, 3, 14, 28, and 52 days after the last injection. BAT was markedly atrophied at 1 day, having less total protein, fewer mitochondria (less total cytochrome oxidase and total uncoupling protein), and fewer cells (less DNA). Atrophy persisted for up to 14 days but had largely disappeared by 28-52 days. A transient reduction in body weight gain and white epididymal adipose tissue weight had also reversed by 28-52 days. We suggest that the rapid atrophy of BAT after capsaicin desensitization is secondary to the loss of sensory neuropeptides in its sensory nerves, neuropeptides that either exert a trophic effect on synthesis of mitochondria or an inhibitory influence on processes that promote degradation of mitochondria. The retardation of the normal age-associated increase in DNA content of BAT in the capsaicin-desensitized rat suggests that sensory neuropeptides might also modulate cell proliferation.