Hormonal control of lipid synthesis in the fat body of the adult female tsetse fly, Glossina morsitans

Abstract

Aqueous extracts of brain, thoracic ganglion or corpora cardiaca of female Glossina morsitans were shown to contain a substance which inhibited the synthesis of lipid from l[U- 14C] leucine by fat cells incubated in vitro. The highest concentration of this substance was found in the corpora cardiaca; approximately 1 × 10 −6 gland pairs μl −1 were required for maximum inhibition. At concentrations greater than 1 × 10 −4 gland pairs μl −1 the lipid synthesis inhibiting factor (hereafter referred to as the LSIF) was inactivated by the presence of a substance which could be removed by gel filtration. The concentration of LSIF in the corpora cardiaca and midbrain varied throughout the reproductive cycle of the female. Net release of LSIF from the midbrain occurred between the 2nd and 7th day of the 9-day reproductive cycle. Net release from the corpora cardiaca began on day 5 and continued until the end of the interlarval period on day 9. Results are consistent with the hypothesis that LSIF is synthesised mainly in the medial neurosecretory cells of the midbrain whereas the corpora cardiaca are the site of storage and release into the haemolymph. LSIF was present in midbrain and corpora cardiaca extracts from male G. morsitans but at lower concentrations than in females. No variation in LSIF concentration could be correlated with the feeding cycle. LSIF activity was not detected in fresh haemolymph but was found at high concentration in boiled haemolymph, suggesting the presence of an inhibitor which was inactivated at high temperature. Preliminary investigations into the nature of LSIF have shown it to be inactivated by proteolytic enzymes and to be recoverable in a single peak from a Sephadex G15 column. Results support the view that LSIF is a peptide hormone which, in conjunction with an inhibitor, controls the lipid synthetic ability of the fat cells of the adult female tsetse fly throughout the reproductive cycle.