The effect of adipokinetic hormones on the levels of inositol phosphates and cyclic amp in the fat body of the desert locust Schistocerca gregaria

The characteristics of the increase in levels of the two second messengers, cyclic AMP (cAMP) and inositol (1, 4, 5) trisphosphate (InsP 3), which occur in the fat body of the desert locust Schistocerca gregaria in response to adipokinetic hormones have been studied. The in vitro dose-response relationships for the effects of the two hormones, AKH-1 and AKH-2, on InsP 3 and cAMP were examined. The increase in InsP 3 is relatively insensitive to hormones with EC 50 values in the 0.1 μM range for both hormones. This is in contrast to the cAMP response which has EC 50 values in the 1 nM range. It was also found that hormone concentrations above 1 μM inhibited the cAMP response but not the InsP 3 response. The time course of the increase in InsP 3 appears to be biphasic, and it is possible that this is due to two separate responses, perhaps occurring in different cell types. No evidence was found for a biphasic time course for the increase in cAMP. In addition to increases in labelling of Ins (1, 4, 5) P 3 a number of metabolites of Ins (1, 4, 5) P 3 also changed in response to adipokinetic hormones.