How sweet it is: sensing low glucose in the carotid body

摘要

The paper by Zhang et al. (2006) in this issue of The Journal of Physiology suggests that the mammalian carotid body may, in addition to sensing hypoxia, function as a peripheral glucosensor. The carotid body might therefore join a group of other extracranial, glucose-sensitive areas including the pancreas, the liver and the hepatic portal vein, and play a role in initiating the reflex, counter-regulatory responses to hypoglycaemia that are initiated in vivo when blood glucose levels fall below the normal range of 4-6 mM (ca 70-110 mg dl~(-1)). This is an intriguing possibility and confirms findings made previously both in vivo and in vitro, but is not without some controversy. Thus, insulin-induced hypoglycaemia does initiate a carotid body-dependent, counter-regulation via elevations in blood glucagon and cortisol (Koyama et al. 2000), but a direct role for glucose sensing has been questioned (Bin-Jaliah et al. 2004) and the stimulus sensed in vivo has been suggested to be hypermetabolic rate rather than hypoglycaemia per se - a suggestion that maybe borne out by a recent, preliminary study on man (Ward, 2006).