The insect adipokinetic hormones (AKHs) are a large family of peptide hormones that are involved in the mobilization of sugar and lipids from the insect fat body during energy-requiring activities such as flight and locomotion, but that also contribute to hemolymph sugar homeostasis. Here, we have identified the first insect AKH receptors, namely those from the fruitfly Drosophila melanogaster and the silkworm Bombyx mori. These results represent a breakthrough for insect molecular endocrinology, because it will lead to the cloning of all AKH receptors from all model insects used in AKH research, and, therefore, to a better understanding of AKH heterogeneity and actions. Interestingly, the insect AKH receptors are structurally and evolutionarily related to the gonadotropin-releasing hormone receptors from vertebrates. Insects constitute the largest animal group on earth and are economically and ecologically extremely important, because most flowering plants depend on insects for their pollination, and insects can be serious pests. Despite the importance of insects, however, our knowledge of their endocrinology is still incomplete. Although in the last 20 years considerable progress has been made with the isolation and identification of peptide hormones from insects (1, 2), the identification of their receptors has remarkably lagged behind (1-4). The adipokinetic hormones (AKHs) are one of the best studied insect neurohormones with more than 30 different family members isolated from over 70 species (1, 2, 4-11). The action of AKH is comparable to that of glucagon from mammals. It contributes to hemolymph sugar homeostasis, but it is also involved in the mobilization of sugar and lipids from the fat body during energy-requiring activities, such as flight or locomotion (1, 2, 4-11). Here we describe the identification of an AKH receptor from the fruitfly Drosophila melanogaster and that from another model insect, the silkworm Bombyx mori. These findings will provide an important lead to find additional insect AKH receptors, which will help us to understand AKH heterogeneity and actions. Materials and MethodsExtraction of the Receptor Ligand. A total of 400 g of third-instar larvae from D. melanogaster (Canton S.) were ground to powder under liquid nitrogen, boiled in 3 vol of deionized water for 20 min, and cooled to 0°C. After acetic acid addition (final pH, 3.0) and homogenization with a Braun food processor, the mixture was centrifuged, and the supernatant was brought to pH 7.0 with a diluted NaOH solution. The extract was then desalted by using several SepPak C18 cartridges (Waters). After being rinsed with 5 ml of H 2 O, each cartridge was eluted with 4 ml of 50% acetonitril in 0.1% trifluoroacetic acid. All eluates were lyophilized and used as a starting material for HPLC (Table 1).HPLC of the Extracts. The HPLC system used was from Shimazu (LC-6A; SPD-6AV; SCL-6B; C-R6A). Columns 1, 2, 5, and 7 (see Table 1) were purchased from Latek (Heidelberg), columns 4 and 6 were purchased from Macherey-Nagel (Düren, Ge...

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