Investigation of the Factors Regulating Ecdysteroid Release By Ovaries From Adult Female Rhodnius Prolixus During Egg Development

Ecdysteroids are released in rhythmic fashion from ovaries during egg development in Rhodnius prolixus. Transfer of ovaries from arrhythmic (LL ) animals to continuous darkness in vitro did not stimulate ecdysteroid release. PERIOD (PER) protein was observed in follicle cells of the ovary only at specific stages of oocyte development in both entrained (LD) and arrhythmic (LL) animals arguing against the presence of an endogenous ovarian clock. I showed that whole and fractionated brain extracts stimulated ecdysteroid release by ovaries from both LD and LL animals. The low molecular weight fraction (containing insulin-like peptides, ILPs) was tenfold more potent than the high molecular weight fraction (containing prothoracicotropic hormone, PTTH). None of recombinant PTTH, vertebrate insulins or corazonin had any significant stimulatory effect on ovarian ecdysteroid release. The circadian rhythm of ecdysteroid release by ovaries appears to be driven exogenously, probably by rhythmic release of unidentified hormones.