Cold exposure potentiates the effect of insulin on in vivo glucose uptake

Abstract

The effects of cold exposure (48 h at 4 degrees C) and insulin injection (0.5 U/kg iv) on the rates of net 2-[3H]deoxyglucose uptake (Ki) in peripheral tissues were investigated in warm-acclimated rats (25 degrees C). Cold exposure and insulin treatment independently increased Ki values in skeletal muscles (soleus, extensor digitorum longus, and vastus lateralis), heart, white adipose tissue (subcutaneous, gonadal, and retroperitoneal), and brown adipose tissue (P less than 0.01). The effects of cold exposure were particularly evident in brown adipose tissue where the Ki increased greater than 100 times. When the two treatments were combined (insulin injection in cold-exposed rats), it was found that cold exposure synergistically enhanced the maximal insulin responses for glucose uptake in brown adipose tissue, all white adipose tissue depots, and skeletal muscles investigated. The results indicate that cold exposure induces an "insulin-like" effect on Ki that does not appear to be specifically associated with shivering thermogenesis in skeletal muscles, because that effect was observed in all insulin-sensitive tissues. The data also demonstrate that cold exposure significantly potentiates the maximal insulin responses for glucose uptake in the same tissues. This potentialization may result from an enhanced responsiveness of peripheral tissues to insulin, possibly occurring at metabolic steps lying beyond the insulin receptor and an increased tissue blood flow augmenting glucose and insulin availability and thereby amplifying glucose uptake.