Octopamine and tyramine regulate the activity of reproductive visceral muscles in the adult female blood-feeding bug, Rhodnius prolixus

The role of octopamine and tyramine in regulating spontaneous contractions of reproductive tissues was examined in the female Rhodnius prolixus. Octopamine decreased the amplitude of spontaneous contractions of the oviducts and reduced RhoprFIRFa-induced contractions in a dose-dependent manner, whereas tyramine only reduced the RhoprFIRFainduced contractions. Both octopamine and tyramine decreased the frequency of spontaneous bursal contractions and completely abolished the contractions at 5×10-7 M and above. Phentolamine, an octopamine receptor antagonist, attenuated the inhibition induced by octopamine on the oviducts and the bursa. Octopamine also increased the levels of cAMP in the oviducts, and this effect was blocked by phentolamine. Dibutyryl cyclic AMP mimicked the effects of octopamine by reducing the frequency of bursal contractions suggesting that the octopamine receptor may act by an Octβ-receptor. The tyramine receptor antagonist yohimbine failed to block the inhibition of contractions induced by tyramine on the bursa suggesting that tyramine may be acting on the Octβ-R in the bursa.