Neuronal regulation of substrate cycle between glucose 6‐phosphate and glucose in brown adipose tissues of cold‐exposed mice

Abstract

The increase in both glucose 6-phosphatase and hexokinase activities in brown adipose tissues of cold-exposed mice probably relates to thermogenesis by the substrate cycle between glucose 6-phosphate and glucose (Watanabe et al.: Anatomical Record 219:39-44, 1987). To clarify the factors causing the simultaneous increase, we examined biochemically the effects of uni- or bilateral surgical denervation of brown adipose tissues, of adrenalectomy, or of streptozotocin injection on the increase in the two activities in the tissues of cold-exposed mice. Further, the effects of denervation on the increase were also examined histochemically. The simultaneous increase in the two activities was inhibited in the denervated tissues of cold-exposed animals in biochemical and histochemical experiments. However, the increase in the activities was not inhibited in the tissues of animals exposed to cold after adrenalectomy or streptozotocin injection. The results suggest strongly that the activation of the substrate cycle in brown adipose tissues of cold-exposed mice is caused by a transmitter released from sympathetic nerve endings, probably norepinephrine.

Characterization of non-cytosolic hexokinase activity in white skeletal muscle from goldfish (Carassius auratus L.) and the effect of cold acclimation

“…In rats exposed to low temperatures, HK activity was 1.15-and 1.17-fold higher in cardiac and gastrocnemius muscles respectively [51]. The exception in mammals was observed in the thermogenic brown adipose tissue of mice, where the increase in HK activity was between 1.9-and 2.5-fold [52,53].…”

Identification and Characterization of Basal and Cyclic AMP Response Elements in the Promoter of the Rat Hexokinase II Gene

“…For example, skeletal muscle glucose utilization is increased by exercise (9), an effect that can be explained in part by the observation that a single bout of acute exercise increases HKII gene transcription, mRNA, and protein in rat skeletal muscle (10,71). Other physiologic stimuli, such as cold stress, swimming, or the administration of ␤-adrenergic agonists, increase total hexokinase activity in rat and mouse brown adipose tissue and muscle (11)(12)(13)(14). The mechanism of these effects is unknown but could involve cAMP.…”