The treatment of locust abdominal fat body in vitro with octopamine caused an elevation in cyclic 3', 5'-adenosine monophosphate (cAMP). However the values varied from one tissue sample to another. Incubation of air sacs separated from fat body cells with octopamine reduced this variability and revealed that octopamine caused a massive increase in air sac cAMP levels but did not alter fat body cAMP concentrations. The air sac cells responded to octopamine in a dose-dependent fashion with a maximum response (10-5M) 40 fold above control levels. The increase in air sac cAMP was sufficient to account for all the increase observed when air sacs and fat body together were incubated with octopamine. Treatment of air sacs with forskolin at 10-5M caused an increase in cAMP but no response was observed with fat body. Octopamine and forskolin acted synergistically to raise air sac cAMP concentrations. The data suggest that air sacs have the potential to make an active response to physiological demands placed upon the insect. The nature of that response is not known. In addition, the absence of changes in cAMP concentration in isolated fat body indicates that cAMP is not the second messenger for octopamine stimulated lipid release from fat body cells. This argues that the octopamine receptor on fat body cells has not yet been characterized.
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