Abstract
Effects of two adipokinetic hormones (Pyrap-AKH and Peram-CAH-II) on the presence of diacylglycerol (DG) molecular species and their fatty acid (FA) constituents in the haemolymph of the firebug Pyrrhocoris apterus were investigated using liquid chromatography (HPLC) and electrospray ionization mass spectrometry (ESI-MS). The results show that DGs with characteristic FAs are preferentially mobilized from the fat body (FB) by the action of both the AKHs produced by P. apterus. Both the macro- pterous and brachypterous morphs have similar DG and FA profiles. A difference in the action of the Pyrap-AKH and the Peram- CAH-II, however, results in distinct differences in the distribution of FAs in the macropterous morph. It seems that C16 to a slight extent and unsaturated C18 FAs mainly play a dominant role in the AKH based action, in particular linoleic acid (18:2), which repre- sents 50-60% of the total DG mobilized. The metabolically active C16 and C18 FAs are preferentially absorbed from the linden seeds and accumulated in the FB. The relationships between AKH action and FA distribution in DGs in P. apterus, compared to other insect species are summarized and discussed in detail.
Highlights
In insects, storage lipids, triacylglycerols (TGs), occur mainly in the fat body (FB), an organ analogous to vertebrate adipose tissue and liver, where they make up about 90% of the total lipids (Arrese & Wells, 1994; Canavoso et al, 1998, 2001; Arrese & Soulages, 2010)
The aim of the present study was to determine whether (1) the DGs and fatty acid (FA) are selectively mobilized by Pyrap-adipokinetic hormones (AKHs) and Peram-CAH-II in P. apterus, (2) the spectrum of lipids present in the bugs differs from that found in their food, and (3) the mobilization of lipids in the adults of the two wing morphs differ
The DG fractions of molecular mass 500–700 Da in the haemolymph of control brachypterous (Fig. 1A1) and macropterous (Fig. 2A1) bugs, and experimental bugs of both wing morphs injected with 10 pmol Pyrap-AKH (Figs 1B1 and 2B1) or 10 pmol Peram-CAH-II (Figs 1C1 and 2C1) were studied in detail using corresponding electrospray ionization mass spectrometry (ESI-MS) analyses (Fig. 1A2 for analysis of the data of Fig. 1A1, Fig. 1B2 for 1B1, Fig. 1C2 for 1C1, and Fig. 2A2 for Fig. 2A1, Fig. 2B2 for 2B1 and Fig. 2C2 for 2C1)
Summary
Storage lipids, triacylglycerols (TGs), occur mainly in the fat body (FB), an organ analogous to vertebrate adipose tissue and liver, where they make up about 90% of the total lipids (Arrese & Wells, 1994; Canavoso et al, 1998, 2001; Arrese & Soulages, 2010). Unlike in vertebrates, where free fatty acids (FAs) are released into the bloodstream and transported bound to albumin, the DGs serve as the major transport lipid shuttle in insect haemolymph, of which more than 90% are sn-1,2-isomers (Van der Horst, 1982; Arrese et al, 1996). HDLp stability and capacity is increased by apolipoprotein-III (apoLp-III) and the mass of the resulting particle, called a low-density lipophorin (LDLp), is about twice that of HDLp. The LDLp transports the DGs to target tissues (mostly muscles) where the DGs are hydrolyzed by lipophorin lipase to free FAs and glycerol. The apoLp-III dissociates from LDLp and is converted to HDLp, which returns to the FB to transport the DG molecule (Canavoso et al, 2001; Van der Horst & Ryan, 2005)
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