Insect cardioactive peptides: neurohormonal regulation of cardiac activity by two cardioacceleratory peptides during flight in the tobacco hawkmoth, Manduca sexta.

The relationship between two cardioactive neuropeptides, the cardioacceleratory peptides (CAPs), and changes in heart rate during flight was investigated in the tobacco hawkmoth, Manduca sexta. In vivo heart recordings from intact, tethered adults revealed a marked increase in heart rate associated with flying. Both anterior-to-posterior and posterior-to-anterior contraction waves showed a measurable elevation in contraction frequency. These changes in heart activity were noted in animals engaged in short (20 min) or long (60 min) bouts of continuous flight. Bioassay of blood taken from flying animals revealed the presence of an activity-dependent, blood-borne cardioacceleratory factor(s). Biochemical analyses of the blood of flying insects on HPLC identified two cardioacceleratory factors which co-eluted with the two CAPs. A depletion in the ventral nerve cord levels of both CAPs was observed during flight. In vivo injections of an anti-CAP monoclonal antibody blocked the increase in cardiac activity associated with flight. These results confirm the hypothesis that both CAPs act as cardioregulatory neurohormones during flight in Manduca sexta.