Changes in haemolymph lipoproteins during locust flight

Structures, assays and receptors for locust adipokinetic hormones

This review is concerned mainly with the adipokinetic hormones (AKHs) of locusts: their molecular conformations, actions and functions and the development of microfiltration assays in vitro. The physiological significance of having multiple hormones with overlapping actions whose efficacy changes during development is discussed in relation to the possibility that these reflect variations in populations of receptors and/or the pharmacokinetics of the peptides. The involvement of second messengers in the transduction mechanism of AKHs is reviewed, and we describe hormone-induced changes of intracellular calcium in single dispersed fat body cells. The structure activity relationships of the three locust AKHs and a number of analogues with variations at the N- and C-termini are discussed. A number of areas are identified where there are gaps in our understanding of these hormones, and some of these will be the focus of our future research.

Identification and initial characterization of adipokinetic hormone-like immunoreactive peptides of rat origin

An antiserum was raised to adipokinetic hormone (AKH), a 10-amino-acid-residue peptide found in the arthropod Locusta migratoria. The antiserum demonstrated not only immunocytochemical reaction with some other arthropod species, but also stained many areas of the rat CNS, certain islet cells of the pancreas, and some anterior pituitary cells. The pattern of staining was unlike that for any known rat neuropeptide or hormone. With the antiserum used as the detection system, HPLC and high-voltage electrophoresis yielded two peptides that were purified to homogeneity from rat hypothalamic median eminence. These peptides have unique amino acid compositions, indicating they may be heretofore unknown rat neuropeptides.

Chiral 1,2-diacylglycerols in the haemolymph of the locust, Locusta migratoria

A 1H-NMR method using chiral shift reagents was applied in the stereochemical analysis of the haemolymph 1,2-diacylglycerols of Locusta migratoria. Conversion of the 1,2-diacylglycerols into 1,2-diacetyl-3-tritylglycerols allowed the accurate determination of the enantiomeric purity, whereas direct trimethylsilylation of the unmodified or hydrogenated haemolymph 1,2-diacylglycerols proved to be less suitable because of signal broadening. In the haemolymph of Locusta, sn-1,2-diacylglycerols with a remarkably high optical purity were found to be present. In the resting locust, at least 96% of the haemolymph 1,2-diacylglycerols have the sn-1,2-configuration, in locusts in which the haemolymph diacylglycerol concentration was elevated by fat body triacylglycerol mobilization induced by flight activity or injection of adipokinetic hormone, over 97% of the 1,2-diacylglycerols is the sn-1,2-enantiomer. The few percent sn-2,3-enantiomer may not have been present initially. Positional distribution of the fatty acids in the fat body triacylglycerols and in the haemolymph sn-1,2-diacylglycerols obtained from locusts after a 2 h flight revealed nearly identical occupation of the sn-2-positions in both acylglycerols. The distribution patterns in the sn-1-position of the 1,2-diacylglycerols and the combined sn-1 and sn-3 positions of the triacylglycerols are compatible with the possible existence of a stereospecific sn-3-triacylglycerol lipase.

Structure of locust adipokinetic hormone, a neurohormone that regulates lipid utilisation during flight

Adipokinetic hormone, isolated from locust corpora cardiaca, has been identified as a blocked peptide: PCA-Leu-Asn-Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH2. The detailed structure is based on mass spectrometric data, substantiated in part by dansyl-Edman and carboxypeptidase data on thermolytic fragments. This is the first peptide hormone from an insect neuroendocrine organ to be fully characterised.