The mechanism of insecticide-induced release of hyperlipaemic hormone from the glandular lobe of the isolated corpora cardiaca (CC) of locusts has been studied using pharmacological agents. 2. Treatment of isolated CC with various insecticides induces the release of hyperlipaemic hormone as judged by bioassay. 3. Reserpinisation of CC (25 micrograms/locust) or treatment of isolated CC with the alpha-adrenergic-receptor blocker phentolamine had no effect on the action of DDT or bioresmethrin, but partially blocked the action of dieldrin and chlorfenvinphos. 4. Treatment of isolated CC with the postsynaptic cholinergic blocker hexamethonium bromide abolished the effect of dieldrin and chlorfenvinphos, but did not block the action of DDT or bioresmethrin. 5. The effects of all the insecticides tested in this study were completely blocked by treatment of the CC with 10(-6) M tetrodotoxin. 6. The results indicate that DDT and bioresmethrin may act directly on the glandular cells via a sodium-dependent mechanism. The results with dieldrin and chlorfenvinphos suggest the presence of two distinct cholinergic pathways, one of which acts via the pre-synaptic aminergic terminals which control the glandular cells, whereas the other acts elsewhere in the CC. Sodium channels are also involved in the ultimate expression of these two insecticides.
