Investigation the effects of insulin and glucagon hormones on fat body metabolism of silkworm, Bombyx mori during pupal period

The insect fat body, which is analogue to vertebrate adipose tissue and liver, is the principle organ that occupies most of the metabolic process, including energy storage, synthesis of carbohydrates, lipids and proteins. In vertebrates, insulin and glucagon hormones play important roles in hormonal control of sugar metabolism, maintaining the homeostasis, growth and development. Various studies showed that peptides, similar with vertebrate peptides, are found in insects. Investigation of their possible effects on insect physiology is substantial for clarification of their evolutionary development period. Because of these complex functions, fat body is a main target for insect hormones such as neural hormones, ecdysone, juvenil hormone, insulin and glucagon like peptides. In this study, we investigated the effects of vertebrate insülin and glucagon hormones on fat body of female Bombyx mori during pupal stage and first day of adult stage.pupal and adult day 0. Vertebrate insulin and glucagon were injected to female insects in a single dose during different days of pupal stage (day 0, 3, 6, 9). Analysis were carried out every 24h after the application till first day of adult stage. Fat bodies were evaluated morphologically by using Periodic Acid Schiff and Hematoxylin&Eosin staining. Fat body sugar, glycogen, lipid, protein contents and acid phosphotase enzyme activities were analyzed spectrophotometrically. Relative abundance of major hemolymph proteins, -lipophorins, storage proteins and 30K proteins-, in fat bodies were detected by using Sodium dodesil sulfate polyacrilamid gel electrophoresis and the gels were stained with silver nitrate. Our results suggested that vertebrate insulin and glucagon showed different effects on insect fat body from those in vertebrates. In addition, their affects are aplication time and developmental day specific. Possible reasons about the differences are presence of other hormonal factors like bombyxin and ecdysone and also timing of critical body weight.