The metabolic actions of glucagon

Abstract

It seems well established that the A-cells of the islets of Langerhans are the main or the only cells containing glucagon in the pancreas. An impressive number of morphological observations showing that the A-cells are influenced by metabolic and hormonal factors constitute at the present time the strongest evidence of the hormonal nature of glucagon. For instance, the observation made initially by Kracht (21), and repeated since by others, that glucagon administration induces an atrophy of the A-cells provides the most direct indication to date that glucagon is indeed secreted and that its secretion is under some “feed-back” control. However, the physiologists have not provided much support for this hypothesis. The consequences of the removal of the A-cells are not clear and many experiments suggest that they would not be very important. A few scattered observations of hypoglycaemia following pancreatectomy in birds (25) or reptiles (27), suggestive as they may be, do not compensate for the lack of conclusive information in mammals. Much weight was given in the past to the differences between depan-creatized and alloxan diabetic animals. Although the evidence may still be valid, it is not as clear-cut as one would like. A substance very similar to glucagon has been isolated from the blood of dogs (23) and rabbits (35) but its chemical identification is not yet conclusive, its pancreatic origin could not be demonstrated, and its concentration in the blood was apparently not influenced by various metabolic or endocrinological factors.