Pharmacology of aminergic receptors mediating an elevation in cyclic AMP and release of hormone from locust neurosecretory cells.

Synaptic activation of the neurosecretory cells within the glandular lobe of the corpus cardiacum of locusts results in the release of bioassayable adipokinetic hormones and an elevation in cAMP. The effectiveness of several putative aminergic neurotransmitters in mimicking these actions of the natural transmitter, and the effects of aminergic antagonists, have been studied. The receptors mediating the release of adipokinetic hormones exhibited a specificity for the monophenolic amines octopamine and synephrine at 10(-7) M. These two amines were also the most effective, at 5 X 10(-6) M, in elevating cAMP levels. Octopamine induced a dose-dependent elevation in cAMP with half-maximal stimulation occurring at 5 X 10(-6) M. 5-Hydroxytryptamine (5-HT) was also capable of elevating cAMP levels, but, unlike the octopamine response, or the response to the natural transmitter, the response to 5-HT was not blocked by the antagonist phentolamine. Gramine was also an effective antagonist of the octopamine-induced response. The results are consistent with the hypothesis that octopamine is the natural transmitter within this neurosecretory system.