Exploring the Role of Rhodtestolin, A Cardio-Inhibitor from the Testes of Rhodnius prolixus, in Relation to the Structure and Function of Reproductive Organs in Insect Vectors of Chagas Disease

Abstract

Rhodtestolin is a cardio-inhibitor that was first discovered in testes extracts of the blood-feeding insect, Rhodnius prolixus. Its role in reproduction remains unconfirmed, but if delivered to the female during spermatophore formation, it may serve to calm the female and/or relax the vaginal muscles to facilitate delivery and storage of the spermatophore. We describe here the anatomy of reproductive organs in R. prolixus and show that rhodtestolin is present in a low-molecular weight fraction of testes extracts separated by gel filtration, as well as in spermatophores delivered to the female during spermatophore formation. We also report that a rhodtestolin-like factor is present in the testes of R. brethesi, Triatoma dimidiata, T. klugi and Nesotriatoma bruneri, other Reduviidae, which are vectors of Chagas disease. Male secretions in insects are known to modify female behavior after copulation, and the presence of rhodtestolin in several genera of Reduviidae suggests that it plays an important role in reproductive success. Determining this role could lead to developing additional population control strategies for these bugs.

Functional Anatomy of the External and Internal Reproductive Structures in Insect Vectors of Chagas Disease with Particular Reference to Rhodnius prolixus

“…Two of the seven have a larger girth and a longer length than the other five, even in the L5 stage. As the testes increase in size during the adult stage, the growth is mainly attributed to the two larger follicles which increase considerably in length and girth [10], which has also been observed in other species of Reduviidae bugs [38].…”

“…They are a bilaterally symmetrical pair of slender blind-ended tubes arising from the sides of the common oviduct [10]. In R. prolixus, they take on a curved to twisted orientation, and when stretched, they can extend from 1/4 to 1/3 down the length of the vagina.…”

“…When a test saline containing rhodtestolin is applied to the isolated heart, the heart becomes flaccid and all beating immediately ceases. Rhodtestolin is a small, heat stable protein, and its dramatic cardio-inhibitory effect is dose dependent and reversible [10]. It has yet to be determined how rhodtestolin concentrated in the testes makes its way to the female, but it is delivered during copulation since extracts of spermatophores removed from the female shortly after the completion of copulation show this cardio-inhibitory effect [10].…”

“…[10]), and has at least two physiological means to help maintain copulation for this length of time. One is sensory; the other is chemical.…”

“…Other researchers have examined physiological processes associated with reproduction [9,10], feeding [11][12][13][14], digestion [15,16] and behaviour [17]. A wealth of knowledge has been gained in close to 100 years of research on this species and with the recent completion of the Rhodnius genome project [18], research on this bug should continue long into the future.…”