Relationships between adenylyl cyclase activity, glucose metabolism, and both intestinal insulin‐like peptide and adipokinetic hormone in mealworm larval fat body

Adenylyl cyclase activity in mealworm larval fat body and its dependence on external Ca2+ concentrations and glucose catabolism pathways in vitro were analyzed for their response to intestinal insulin-like peptide (ILP) and synthetic locust adipokinetic hormone I (AKH-I). Dose-response curve for cAMP accumulation was obtained with increasing doses of ILP. The effects of ILP were ten-fold lower than those of AKH-I. Forskolin and IBMX provoked very high levels of cAMP accumulation but IBMX did not potentiate the effects of ILP on cAMP accumulation. Accumulation of cAMP after a treatment with ILP involves a Ca2+ influx via the opening of L-type voltage gated channels. The cyclic AMP analogue chlorophenyl thio-cAMP as well as AKH-I induced a decrease in the utilization of the pentose cycle while the effects of ILP were totally opposite. Finally, the antagonism between ILP and AKH-I on glucose metabolism results from a participation of different transduction pathways (Ca2+-dependent and Ca2+-independent, respectively), probably located in the same target cells, thus suggesting the involvement of mechanisms similar to those existing in mammals. © 1996 Wiley-Liss, Inc.