In vitro hormonally induced variations of glucose catabolism in mealworm fat body tissue were examined by a microradiorespirometric method. An insulin-like peptide (ILP) extracted from the midgut of last larval instar mealworm larvae significantly modified glucose catabolism and was dependent on energy metabolism and on the Ca2+ concentration in the culture medium. Using two different labelled substrate molecules, the stimulatory effects of ILP (compared with those of mammalian insulin) on the relative use of the pentose cycle as opposed to the glycolytic-citric acid cycle by the mealworm fat body were measured in vitro. Metabolic variations were evaluated using either [1-14C]glucose or [6-14C]glucose as substrates. Time course and dose-response curves of ILP and the hormonally induced variations in total CO2 and 14CO2 kinetics were determined. Modification in the specific radioactivity kinetics of 14CO2 derived from [1-14C] glucose and [6-14C]glucose molecules under hormonal effects were observed. As demonstrated in in vivo studies, ILP stimulated the relative utilization of the pentose cycle. However, this effect was observed much more rapidly, but for a shorter time, with fat body in vitro. Mammalian insulin produced similar, but not identical effects. Variations in transmembranous Ca2+ cellular exchanges, induced by either EGTA, nifedipine, or calcium ionophore ionomycin included in the culture medium, indicated that the stimulatory effects of ILP depends on this cation.
Glucose metabolism by Tenebrio molitor larval fat body tissue was studied in vitro by means of a microradiorespirometric method and the effects of either natural or synthetic catabolic hormones were evaluated. The use of this microradiorespirometric method allowed us to measure glucose catabolism in small pieces of tissue with good sensitivity.The metabolic modifications (relative and absolute) induced in the activities of the pentose cycle and glycolysis-Krebs cycle, by larval mealworm Corpora cardiaca (CC) purified extracts, were compared with those produced by synthetic locust AKH I and mammalian glucagon. These metabolic variations were evaluated by measuring total C02 and by using either [l-14Clglucose or [6-'4Clglucose molecules as substrates. The kinetics of 14C02 production and the dose-response curves of hormones were determined. The total expired COz increases significantly (17-26%) during treatment with all of the hormones studied.Modifications to the kinetics of the specific radioactivity and the cumulative yields of 14C02 derived from [l-14C]glucose and [6-'4Clglucose under the influence of each of the hormones were recorded. CC extracts and AKH I rapidly (15 min) diverted glucose from pentose cycle ( -45%); glucose oxidation was increased ( + 26%), this effect appearing later (75 m i d . Mammalian glucagon rapidly and durably increased glucose catabolism both via the pentose cycle ( + 35%) and by the glycolytic pathway ( + 200%). o
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