In vitro studies on the effects of octopamine on locust fat body

The effects of octopamine on the fat body of locusts in vitro have been examined. The isolated fat body responded to octopamine by releasing lipid in a dose-dependent manner. Maximal stimulation was obtained with 5 × 10 −6 M octopamine. The octopamine stimulated release of lipid was blocked by α-adrenergic receptor antagonists but unaffected by β-adrenergic receptor antagonists. Octopamine was more potent than synephrine, dopamine, or tyramine in eliciting the response. Octopamine (5 × 10 −6 M) in the presence of IBMX, resulted in a six- to sevenfold elevation of cyclic AMP in the fat body; this response was also blocked by α- but not β-adrenergic receptor antagonists. Cyclic GMP levels were unaffected by octopamine. Adipokinetic hormone (AKH) in the presence of IBMX, also stimulated an elevation in cyclic AMP in the fat body, and stimulated the release of lipid. Unlike the octopamine stimulation, however, the AKH effect was not inhibited by the α-adrenergic receptor antagonists. Furthermore, AKH inhibited protein synthetic activity of fat body, while octopamine was without effect. It is concluded that a release of lipid from fat body of locusts is probably mediated by a rapid activation of an octopamine-sensitive adenylate cyclase. Furthermore, the mechanism of action and the receptors for octopamine and AKH are different.