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Investigations on the mode of action of the crustacean hyperglycemic hormone (CHH) revealed an increase of CAMP and cGMP concentrations in the abdominal muscle after the application of this hormone, indicating a second messenger mechanism comparable to the mechanism already known for vertebrate peptide hormones. A maximal stimulation of CAMP was shown 10 min after the injection of the hormone, whereas in cGMP, a constant increase up to 20 min was demonstrated. It should be expected that this elevation is due to an activation of adenylate and guanylate cyclase, but we cannot rule out the possibility of an inhibition of the phosphodiesterases caused by the hormone, which would also result in an increase of the cyclic nucleotides. The time course of the adenylate cyclase activity after hormone injection shows a pattern similar to the one we know for the CAMP concentrations. As one should expect, there is a little time delay between the action of the adenylate cyclase and the increase of CAMP. CAMP phosphodiesterase shows changes in activity comparable to CAMP increase. This increase obviously is due to the elevated CAMP concentrations and not to an immediate action of the hormone on phosphodiesterase. cGMP phosphodiesterase follows more or less the same pattern, an observation which coincides with the cGMP elevation curve. Guanylate cyclase was not measured. From these results, it seems clear that the increase in cyclic nucleotides after hormone injection is due to the action of cyclases and not to an inhibition of phosphodiesterases. |
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