Pharmacological properties of octopamine-2 receptors in locust neuroendocrine tissue

In Locusta, the glandular lobe of the corpus cardiacum is the site of synthesis, storage, and release of adipokinetic hormones. The release of these hormones is synaptically controlled by octopaminergic axons and a role for cAMP in this process has been proposed. We have further examined the time-course and pharmacological characteristics of the octopamine-mediated increase in cAMP accumulation within the glandular lobe. Octopamine, in the presence and absence of 3-isobutyl-1-methylxanthine mediates a dose-dependent increase in cAMP content, reaching a maximum within a 10 min exposure period. Within 15 min these levels subsequently decline to basal levels or to levels seen after exposure to 3-isobutyl-1-methylxanthine alone. The diterpene forskolin stimulates a dose-dependent increase in cAMP accumulation. Minor elevations in cGMP content occur following exposure to 3-isobutyl-1-methylxanthine or octopamine although these increases are markedly lower than the increases in cAMP content. A pharmacological profile of the octopamine receptors established by treating glandular lobes with various aminergic agonists and antagonists suggests that they belong to the octopamine-2 class.