Cyclic AMP in the Malpighian tubule fluid and in the urine of Rhodnius prolixus.

We demonstrate the presence of cyclic adenosine monophosphate (cAMP) in the fluid secreted by isolated Malpighian tubules of Rhodnius prolixus. In addition, we show that fifth-instar R. prolixus excrete cAMP in the urine after a meal of human blood. Nonstimulated isolated Malpighian tubules secrete small amounts of cAMP that increase about 10-fold after the addition of 5-hydroxytryptamine (5-HT). 5-HT is known to mimic R. prolixus diuretic hormone. The present findings demonstrate that 5-HT also acts via cAMP. The presence of cAMP in the rectal sac of the insect could be of importance in the differentiation of Trypanosoma cruzi and in the cycle of Chagas disease.