Recently it has been shown that 5-hydroxytryptamine (5-HT) even at concentrations of the order of io" M/1 will stimulate fluid secretion by the Malpighian tubules of two insect species, Rhodnius prolixus Stal and Carausius morosus (Maddrell, Pilcher & Gardiner, 1969). In order to find out more about this interaction the activity of a range of substances chemically related to 5-HT has been studi...
