Adipokinetic Hormones

Introduction

The discovery of adipokinetic hormones (AKH) dates back to half a century. Researchers found that the extract of corpus cardiacum of periplaneta americana could increase the amount of carbohydrates in hemolymph, and the extract of the locust corpus cardiacum could also obviously increase the lipid level in hemolymph. The above evidence indicates that certain hormone in the insect's parenchyma is able to regulate the metabolism of carbohydrates and lipids. In 1976, scientists first discovered AKH from locust and its amino acid sequence has been elucidated. In general, AKH contain 8-10 amino acid residues, a pyroglutamate residue at the N-terminus, and an amide group at the C-terminus. The main function of AKH is to induce the degradation of various substrates of fat bodies, providing energy for energy-consuming activities, especially flying.

Mechanism of action

AKH are derived from the gland of corpus cardiacum. The neurosecretory gland is connected to the brain of insects, which is equivalent to the pituitary of the vertebrate. After being released into the hemolymph system, AKH reach the specific areas such as a fat body, and binds to its corresponding membrane receptor, resulting in Gs or Gq protein coupling, the activation of adenylate cyclase and phospholipase C. And then Ca²⁺ and cAMP are significantly increased. Eventually, glycogen phosphorylase and TAG lipase is activated. Trehalose and diacylglycerol provide energy for energy-consuming physiological processes such as exercise.

Application of Adipokinetic Hormones

AKH are a class of neuropeptide toxins. Neuropeptides are a very important class of regulatory factor that play a key role in multiple physiological processes such as metabolism, homeostasis, development and reproduction. The mechanism of action of AKH has become the key to the identification and utilization of the dynamic balance of insect energy. At the same time, although insects and vertebrates have great differences in anatomy and physiology, their regulation mechanisms of energy dynamic balance are very conservative in the evolution process. Therefore, figuring out the regulation mechanism of insect energy dynamic balance also contributes to further understanding and control of human obesity.

References

1. Diederen, J. H., Oudejans, R. C., Harthoorn, L. F., & Van Der Horst, D. J. (2002). Cell biology of the adipokinetic hormone‐producing neurosecretory cells in the locust corpus cardiacum. Microscopy research and technique, 56(3), 227-236.
2. Oudejans, R. C., Harthoorn, L. F., Diederen, J. H., & Van Der Horst, D. J. (1999). Adipokinetic hormones: coupling between biosynthesis and release. Annals of the New York Academy of Sciences, 897(1), 291-299.