In order to explain the effects of these two hormones on cAMP levels in this cells I’m going to describe each of the three cases on the graph.
In the first column of the first case, in which only acts Nerve Growth Factor(NGF) the cAMP levels are of 20 micromoles. When the A peptide is added to the NGF, the amount of cAMP gets reduced more than a half of its initial value.
In the first column of the second case, in which only acts Bradykinin, the cAMP levels are a little bit more than 20 micromoles. When the peptide A is added, the amount of cAMP does not decrease significantly.
The last case shows that when NGF and Bradykinin are combined together the Adenyl Cyclase produces a lot of cAMP (almost 80 micromoles), and when the A peptide is added the production of cAMP decreases abruptly.
The solution I propose is that NGF has more related with the G protein that activates Adenyl Cyclase, for that reason it gets more affected when the A peptide prevents the exchange of GDP for GTP.
The Bradykinin is not related with the G protein.
NGF is related with the G protein (couple receptor) and for that reason it gets much affected by the A peptide.