Changes in cyclic AMP and cyclic GMP concentrations during the action of 5-hydroxytryptamine on an insect salivary gland

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Abstract
Salivary glands from adult blowflies (C. erythrocephala Meigen) were studied in vitro. The time course of changes in cAMP content of the glands was followed at different concentrations of 5-hydroxytryptamine. There was an immediate biphasic rise and fall in cAMP content, followed by a slower rise and subsequent gradual decline. The initial rise preceded the onset of fluid secretion by the glands. Rises in cAMP content were inhibited by compound RMI 12330A (an adenylate cyclase inhibitor) and were halted after about 15-20 s if the glands were deprived of Ca2+. Theophylline (a phosphodiesterase inhibitor) abolished the decline phase of the fast response. Losses of cAMP from the glands either to the bathing medium or to the saliva were small and could not account for the rapid fall found. cGMP is not involved in the process of initiating secretion in the blowfly salivary gland.