Effect of allatectomy on fat body lipogenic enzymes of the male desert locust during adult development

The effect of allatectomy on the changes in activity of enzymes concerned with the conversion of dietary carbohydrate to lipid by the fat body during development has been investigated. The enzymes studied were phosphofructokinase, pyruvate kinase, malic enzyme, glucose-6-phosphate dehydrogenase isocitrate dehydrogenase, ATP citrate lyase, and fructose-1,6-diphosphatase. All operations were carried out at 4 days after emergence and allatectomized insects were compared with sham operated controls. The sham-operated controls showed similar enzyme changes to normal insects during development, thus the physical stress of the operation does not affect fat body metabolism.     

A comparison of the properties of the phosphofructokinases of the fat body and flight muscle of the adult male desert locust

1. Phosphofructokinase was isolated, and partially purified by ammonium sulphate fractionation, from the fat body and flight muscle of the desert locust. 2. Ammonium sulphate appears to stabilize the enzymes, but does not activate them. 3. Both flight-muscle and fat-body enzymes give sigmoidal hexose monophosphate concentration-activity curves, which are characteristic of regulatory enzymes. 4. At low ATP concentrations both the enzyme activities increase rapidly with increasing ATP concentrations, but above an optimum concentration ATP becomes inhibitory. This optimum concentration is 0.2mm for the fat-body enzyme and 0.1mm for the flight-muscle enzyme. 5. AMP activates both the enzymes; half-maximal activation occurs at 10mum in each case, the effect being independent of substrate concentration. 6. 3',5'-(cyclic)-AMP (0.5mm) and P(i) (1mm) activate the flight-muscle enzyme, but have no effect on the fat-body enzyme. 7. FDP (1mm) inhibits both enzymes, and with the flight-muscle enzyme this inhibition is increased by increasing the ATP concentration. 8. Citrate, phosphoenolpyruvate and alpha-glycerophosphate have no effect on either enzyme under the assay conditions used. 9. The properties of phosphofructokinases from the locust are compared with those of phosphofructokinases from other sources.     

A comparison of the properties of the pyruvate kinases of the fat body and flight muscle of the adult male desert locust

1. The pyruvate kinases of the desert locust fat body and flight muscle were partially purified by ammonium sulphate fractionation. 2. The fat-body enzyme is allosterically activated by very low (1mum) concentrations of fructose 1,6-diphosphate, whereas the flight-muscle enzyme is unaffected by this metabolite at physiological pH. 3. Flight-muscle pyruvate kinase is activated by preincubation at 25 degrees for 5min., whereas the fat-body enzyme is unaffected by such treatment. 4. Both enzymes require 1-2mm-ADP for maximal activity and are inhibited at higher concentrations. With the fat-body enzyme inhibition by ADP is prevented by the presence of fructose 1,6-diphosphate. 5. Both enzymes are inhibited by ATP, half-maximal inhibition occurring at about 5mm-ATP. With the fat-body enzyme ATP inhibition can be reversed by fructose 1,6-diphosphate. 6. The fat-body enzyme exhibits maximal activity at about pH7.2 and the activity decreases rapidly above this pH. This inactivation at high pH is not observed in the presence of fructose 1,6-diphosphate, i.e. maximum stimulating effects of fructose 1,6-diphosphate are observed at high pH. The flight-muscle enzyme exhibits two optima, one at about pH7.2 as with the fat-body enzyme and the other at about pH8.5. Stimulation of the enzyme activity by fructose 1,6-diphosphate was observed at pH8.5 and above.     

The relationships between corpora allata and fat body and haemolymph lipids in the adult female desert locust

Allatectomy of 1-day-old female desert locusts resulted in an accumulation of lipid in the fat body. This accumulation of lipid was due to the continuation of lipid deposition in the fat body after the period of somatic growth. Somatic growth and feeding activity were unaffected by allatectomy, and so could not be indirect causes of fat body lipid accumulation. Lipid accumulation in allatectomized locusts is more likely to be related directly to a lack of juvenile hormone. Implantation of active corpora allata into 1-day-old adult female locusts resulted in a premature development of oöcytes and a decrease in fat body lipid accumulation; somatic growth was not inhibited. Implantation of active corpora allata into old allatectomized locusts resulted in a decrease in the fat body lipid content and the onset of oöcyte development. The lipid synthetic activity of the fat body, measured by the incorporation of ¹⁴C-actate into total fat body lipid, was greatly increased in allatectomized locusts after the period of somatic growth. The protein synthetic activity of the fat body, measured by the incorporation of ³H-leucine into total fat body protein, remained low after the period of somatic growth in allatectomized insects. Juvenile hormone might thus have a dual effect on fat body metabolism, that is suppressing lipid synthesis and stimulating vitellogenic protein synthesis. Increased synthesis of lipid by the fat body would then account for the accumulation of lipid in the fat body after allatectomy. Inhibition of release of lipid from the fat body is unlikely to play a part in the accumulation as allatectomy had no effect on haemolymph lipid concentrations.     

Chloromethyl ketones are insulin-like stimulators of lipid synthesis in locust fat body

Nα-p-tosyl-L-lysine chloromethyl ketone (TLCK) stimulates lipid synthesis in locust fat body in vitro, and is able to reverse the inhibitory effects of AKH-I on lipid synthesis. Effective stimulatory concentrations of TLCK were in the range of 0.2–1.0 mM. Similar stimulatory effects were also achieved with phenylalanine chloromethyl ketone (PheCK) and leucine chloromethyl ketone (LeuCK), but not with tosyl-phenylalanine chloromethyl ketone (TPCK), dansyl-glu-gly-arg-CK, chloroacetone, chloroacetic acid, chloroacetamide, chloroacetaldehyde, chloroacetyl-L-leucine or acetylated or fluorescamine-labelled TLCK, PheCK, and LeuCK. The level of stimulation caused by TLCK was dependent on incubation time, so that after a 5-h preincubation of fat body tissue with TLCK the stimulated rate was severalfold higher than the control. TLCK also increased the rate of uptake of trehalose and uridine, but not glucose, deoxyglucose or glycine. Increasing concentrations of bovine serum albumin (BSA) in the incubation medium caused a reduction in the rate of TLCK-stimulated acetate uptake, such that levels of uptake were no higher with 1% BSA than in the controls. A range of more specific protease and kinase inhibitors was tested, but none caused stimulation; thus the mode of action of TLCK on the stimulation of acetate uptake has yet to be identified. Elucidation of the mode of action of TLCK may facilitate the development of novel compounds for insect pest control. Arch. Insect Biochem. Physiol. 39:9–17, 1998. © 1998 Wiley-Liss, Inc.     

Hormonal control of diacyl glycerol mobilization from fat body of the desert locust,Schistocerca gregaria

The action of adipokinetic hormone in stimulating mobilization of diacyl glycerol from locust fat body was studied in vitro. For optimum lipid mobilization haemolymph protein and calcium ions were required, and the amount and time course of release were dependent on the hormone concentration. Dibutyryl cyclic AMP or theophylline mimicked the action of the hormone and a synergistic effect of theophylline with hormone was found. Purified adipokinetic hormone with theophylline increased the concentration of cyclic AMP in fat body and stimulated the incorporation of [³H]-adenine into cyclic AMP.A lipase was present in fat body extracts which hydrolysed triacyl glycerol mainly to diacyl glycerol plus fatty acid. The activity of this enzyme was low, and attempts to activate it with hormone were unsuccessful.     

Juvenile hormone action on locust fat body

Production of vitellogenin (Vg) in fat body of adult female Locusta migratoria is abolished by removal or inactivation of the corpora allata and restored by administration of (RS)-methoprene. Juvenile hormone III injection alone has little effect, but when it is injected together with the JH esterase inhibitor OTFP, active Vg synthesis is induced. This supports the assumption that methoprene acts in place of the natural hormone in this system. When fat body from vitellogenic females is maintained in synthetic medium for 48 hr, the proportion of Vg in the secreted protein drops greatly, but when methoprene is present in the medium the proportion of Vg is sustained. When fat body from JH-withdrawn locusts, in which Vg synthesis has declined to zero, is cultured with methoprene, Vg synthesis is re-induced. These results show that the JH analog can act directly on locust fat body to bring about expression of the Vg genes. Experiments to optimize JH action on fat body in vitro are continuing.     

The body temperature of the desert locust Schistocerca gregaria

Summary The internal equilibrium body temperatures of hoppers (nymphs) of Schistocerca gregaria were studied in the field. The data obtained are here compared with theoretical estimates of the thermal balance resulting from the factors assumed to be concerned in heat loss and heat gain.In the field, the equilibrium body temperature of quiescent hoppers shaded from direct sunshine was up to 3.2° higher than the air temperature when the latter was about 25° or less, but was lower than the air temperature when this was above about 31°. In sunlight, body-temperature excesses increased linearly with total radiation intensity between 0.15 and 1.25 cal/cm²/min. Differences in orientation to the sun gave rise to differences in equilibrium body temperature of as much as 6°. At relatively low radiation intensities (about 0.5 cal/cm²/min) the equilibrium body temperatures were found to vary with a power of the wind speed of about 0.35. There were no demonstrable significant differences in equilibrium body temperature or rate of change of body temperature between hoppers having opposite extremes of possible coloration.Except in hoppers shaded from sunlight and those exposed to low radiation intensities there was good agreement between the observed equilibrium temperatures and those expected on theoretical grounds. This provides evidence of the relative importance of the factors concerned in thermal balance.The relation between body temperature and behaviour is discussed.

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Zusammenfassung Das innere Gleichgewicht der Körpertemperatur von vorzugsweise fünften Larvenstadien der Wüstenheuschrecke wurde unter Freilandbedingungen in Beziehung zu Lufttemperatur, relativer Luftfeuchtigkeit, Strahlungsintensität, Windgeschwindigkeit und Aktivität gemessen.Die verschiedenen Faktoren, die das Temperaturgleichgewicht der Heuschrecken beeinflussen, werden theoretisch behandelt. Die unter bestimmten Kombinationen der Umweltbedingungen zu erwartenden Gleichgewichts-Körpertemperaturen werden aus den theoretischen Werten für die verschiedenen beteiligten Faktoren errechnet und mit den unter entsprechenden Freilandbedingungen beobachteten Werten verglichen.Ohne Sonneneinstrahlung und unter relativ windstillen Bedingungen wurde bei ruhenden Larven des fünften Stadiums eine Gleichgewichts-Temperatur des Körpers gefunden, die bis zu 3,2° höher lag als die Lufttemperatur, wenn diese ca. 25° oder weniger betrug. Dieser Überschuß hatte eine abnehmende Tendenz bei Lufttemperaturen bis zu etwa 31° und über dieser Schwelle waren die Gleichgewichts-Temperaturen des Körpers im allgemeinen niedriger als die entsprechenden Lufttemperaturen. Theoretisch würde zu erwarten sein, daß unter diesen Umweltbedingungen das Temperaturgleichgewicht des Körpers in allen Niveaus annähernd der Lufttemperatur entspräche. Folglich scheint hier ein physiologischer Mechanismus zu bestehen, mit dessen Hilfe die Insekten in Abwesenheit von Sonnenschein und unter den Bedingungen schwacher Konvektion ihre Körperausgleichstemperaturen bei niedrigen Lufttemperaturen erhöhen, bei hohen senken können.Es war nicht möglich, im Freiland nachzuweisen, daß Unterschiede in der relativen Luftfeuchtigkeit irgendeinen signifikanten Einfluß auf die ausgeglichenen Körpertemperaturen in dem untersuchten Bereich (Sättigungsdefizit von 2 bis 27 mm) ausübten. Die erwarteten maximalen Differenzen der Gleichgewichts-Körpertemperaturen lagen in diesem Bereich des Sättigungsdefizits in einer Größenordnung von nur 0,5°.Unter relativ ruhigen Freilandbedingungen zeigten die Heuschrecken im Sonnenschein Körpertemperaturüberschüsse, die bei einer totalen Strahlungsintensität zwischen 0,15 und 1,25 cal/cm²/min annähernd linear anstiegen (von einem Mittel von 2–10° bei fünften Larvenstadien). Die in diesem Strahlungsintensitätsbereich gemessenen Übertemperaturen des Körpers stimmten einigermaßen gut mit Werten überein, die von anderen Untersuchern unter Laboratoriumsverhältnissen festgestellt wurden. Unter 0,40 cal/cm²/min waren die beobachteten Körpertemperaturüberschüsse im allgemeinen höher als theoretisch zu erwarten gewesen wäre. Die Körpertemperatur von Larven des ersten Stadiums nahm rascher zu als die von Larven des fünften, jedoch nur bis zu einem niedrigeren Niveau; auch das stimmte gut mit den theoretischen Vorstellungen und mit der Laborerfahrung überein. Die Einstellreaktion der Heuschrecken zur Sonne ergab beobachtete Unterschiede in der Gleichgewichts-Körpertemperatur bis zu 6° zwischen Larven des fünften Stadiums, die sich in Richtung der Sonnenstrahlen eingestellt hatten, und solchen, die im rechten Winkel zur Sonnenrichtung auf dem Boden standen; die erwarteten Unterschiede waren von der gleichen Größenordnung.Im Sonnenschein variierten die erwarteten Intensitätsproportionen zwischen der Ausgleichstemperatur und der Windgeschwindigkeit zwischen 0,5 und 0,6 mit dem Sättigungsdefizit. Bei Strahlungsintensitäten von etwa 1,10 cal/cm²/min stimmten die beobachteten Körpergleichgewichtstemperaturen engstens mit den erwarteten überein, aber bei geringeren Strahlungsintensitäten von etwa 0,50 cal/cm²/min variierten die Meßwerte mit einer Intensitätsproportion zur Windgeschwindigkeit von etwa 0,35. Darin zeigt sich möglicherweise, daß bei niederen Strahlungswerten die Körperausgleichstemperaturen zu höheren Werten tendieren als zu erwarten war.Das beobachtete Ansteigen der Körperausgleichstemperatur von ungefähr 1° bei dritten Larvenstadien und von 2–3° bei fünften Larvenstadien befindet sich in Übereinstimmung mit dem für entsprechende Umweltbedingungen errechneten.Zwischen Larven extrem entgegengesetzter Färbungstypen konnten keine Unterschiede in den Körperausgleichstemperaturen oder dem Ausmaß der Körpertemperaturänderung nachgewiesen werden.Mit Ausnahme der vor direkter Sonnenbestrahlung geschützten Heuschrecken unter relativ ruhigen Bedingungen und der Heuschrecken, die niederen Strahlungsintensitäten ausgesetzt waren, bestand eine gute allgemeine Übereinstimmung zwischen den beobachteten und den erwarteten Gleichgewichts-Körpertemperaturen. Es wurde deshalb geschlossen, daß die durchgeführten Bestimmungen Beweise für die relative Bedeutung der für den Temperaturhaushalt verantwortlichen Faktoren darstellen. Zur Erzeugung beträchtlicher Überschüsse der Körpertemperatur über die Lufttemperatur hat die Strahlung die größte Bedeutung. Für den Wärmeabfluß nach außen werden die durch Konvektion entstehenden Wärmeverluste, die insgesamt 94% oder mehr betragen, als bei weitem am wichtigsten angesehen.Einige mögliche Beziehungen zwischen Körpertemperatur und Verhalten werden besprochen.

     

Effect of ambient temperature on lipid metabolism in brown fat during the perinatal period

• 1.1. Norepinephrine-induced lipolysis, cyclic AMP production and glycerokinase activity were measured, in vitro, in the brown fat of rats born and reared at either 28° or 16°C during the first 3 weeks of life.
• 2.2. During the first two postnatal days, lipolytic activity in the tissue was lower than in the foetuses at both ambient temperatures At day 10, increased values of the parameters under consideration were similarly observed in both groups.
• 3.3. However, the hormonal regulation of lipolysis seemed to be quite different from that found in adult cold-acclimated rats.
• 4.4. At day 21, the cold-induced characteristics of lipid metabolism in brown fat were observed in the 16°C exposed rats, whereas a loss of tissue stimulation occurred in the 28°C exposed ones.

     

Effect of caffeine on the body fat and lipid metabolism of rats fed on a high-fat diet

The intake of caffeine (CF) at 0.025, 0.05 or 0.1% for 21 days progressively reduced the body fat mass and body fat percentage in Sprague-Dawley (SD) rats fed on a high-fat diet with increasing administration level. Moreover, CF increased the serum concentrations of catecholamines and free fatty acids in SD rats orally administered with CF (5 mg/kg). These results suggest that the intake of CF reduced body fat by lipolysis via catecholamines. CF has potential as a functional food ingredient with an anti-obesity action.     

Effects of tea catechins on lipid metabolism and body fat accumulation

Long-term feeding of tea catechins suppressed body fat accumulation in high-fat diet-induced obesity in mice, and that their effects might be attributed, at least in part, to the activation of hepatic lipid metabolism. Consecutive intake of tea catechins (588 mg/day) reduced body fat, especially abdominal fat in humans. These results demonstrate that intake of tea catechins is beneficial for body fat accumulation.