Tachykinin stimulation effects on α-amylase, protease and lipase activities in midgut of American cockroach, Periplaneta americana (Blattodea: Blattidae)

The effect of a neuropeptide, the tachykinin on α-amylase, protease and lipase activities in the midgut of American cockroach, Periplaneta americana (Linnaeus) is evaluated . Immunohistochemical reactivities against tachykinin (tachykininir) were detected in the midgut. Tachykinin-ir cells in three regions (anterior, median and posterior) of the midgut were counted in normally fed, starved for four weeks and refed cockroaches. The number of tachykinin-ir cells decreased during 4 weeks of starvation and increased 3 h after refeeding. The results of the competitive ELISA were consistent with the profile of immunohistochemical reactivity. Incubation of the dissected midgut with tachykinin led to an increase in α-amylase, protease and lipase activities while the buffer remained ineffective. Tachykinin injection into the hemocoel increased α-amylase, protease and lipase activities, but PBS injection showed no sign of effectiveness. The results seggest that nutrients upregulate midgut cells secreting tachykinin causing further activities of digestive enzymes.