Studies on assimilation, mobilization, and transport of lipids by the fat body and haemolymph of Pyrrhocoris apterus

Abstract

The incorporation and release of lipid in vitro by the fat body of adult female Pyrrhocoris apterus, and the lipid content and composition of the haemolymph were examined in relation to the cyclic growth and diminution of the fat body and the probable contribution of lipid from the fat body to the developing oöcytes. The fat body released lipid at a constant rate during most of the reproductive cycle and in non-reproducing (diapausing or ovariectomized) females. On the other hand, the rate at which the fat body incorporated lipid in vitro was markedly reduced during the period of major oöcyte growth (days 3–5 following the larval-adult ecdysis), while it remained high during the corresponding period after ovariectomy and was low in diapause. The change in rate of lipid incorporation appears to account for the change in the fat body from net accumulation of lipid (days 1–3) to net loss of lipid (during rapid oöcyte growth on days 3–5). Several characteristics of lipid incorporation and mobilization in vitro by the Pyrrhocoris fat body are different from those of the few other insect species studied and from mammalian adipose tissues. In Pyrrhocoris, haemolymph or bovine serum albumin is required for the maximum rate of incorporation, which is ten times higher than that reported for other insects. The fat body of Pyrrhocoris is not dependent on an external source of glyceride-glycerol for the esterification of fatty acids. Lipid is released at a much slower rate than found in other insect species. The primary class of lipid released is triglyceride, the form in which lipid is stored in the fat body and which predominates among lipid classes in the haemolymph. The importance of the method used to label the fat body is discussed. The haemolymph of adult female Pyrrhocoris is normally filled with lipid droplets and lipid-filled cells which closely resemble fat body cells. It is suggested that the release of lipid-filled cells from the fat body constitutes one phase of the mobilization of fat body lipid.