Modified adipokinetic peptides containing two tryptophan residues and their activities in vitro and in vivo in Locusta.

Locusta migratoria has three adipokinetic hormones, adipokinetic hormone-I, II and III. Adipokinetic hormone-III (<QLNFTPWWa) is surprisingly potent (EC50 = 1.33 x 10(-10)mol x 1(-1)) compared with other adipokinetic hormones (EC50 > or = 5.33 x 10(-10)mol x 1(-1)) at inhibiting acetate uptake into locust fat body in vitro, especially so when it is only moderately potent in mobilizing lipid in vivo. The Trp7 in adipokinetic hormones-III, alongside the Trp8 characteristic of adipokinetic hormones, is not seen in any other adipokinetic hormones. To test whether this is hormone-III in the assay in vitro, novel peptides were synthesised to include or remove this structural motif. Thus <QLNFTPWWGTa (Trp7-Locusta-adipokinetic hormone-I or [Gly8a-Thr8b]-Locusta-adipokinetic hormone III); <QLNFTPNWa (des[Gly9-Thr10]- Locusta-adipokinetic hormone-I or Asn7-Locusta-adipokinetic hormone III); <QLNF-SAWWa (Trp7-Locusta-adipokinetic hormone-II) and <QVNFSTWWa (Trp7-Acheta-adipokinetic hormones) were tested both in vitro and in vivo. Except for Trp7-adipokinetic hormone-I in the acetate uptake assay, each of these analogues is less potent then its respective parent, irrespective of the assay. However, the acetate uptake response is highly tolerant of peptides containing Trp7-Trp8, whereas this motif markedly reduces potency in the lipid assays. The different responses exploited in these assays may be exerted through different receptor populations.