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Summary
The brain-retrocerebral complex (br-complex) of Rhodnius prolixus was found both to contain and release neuropeptides related to Bombyx mori PTTH and bombyxin. A > 10 kDa peptide fraction obtained from extracts and incubation media of br-complex exhibited high steroidogenic activity on Rhodnius prothoracic glands and reacted with a Bombyx PTTH antibody on dot blots. The release from the Br-complex of this immunoreactive peptide fraction showed a daily rhythm: high release during the night and little on no release during the day. On Western blots, a single 68 kDa peptide in the > 10 kDa peptide fraction was recognized by the Bombyx PTTH antibody and was also released rhythmically during a day. This peptide was reduced to a doublet of about 17 kDa that retained immunoreactivity. Double immunoprecipitation of the > 10 kDa peptide fraction from brain media using the Bombyx PTTH antibody and agarose-bound secondary antibody removed the steroidogenic activity in this fraction; it also removed the 68 kDa peptide on Western blots. A bombyxin antiserum recognized a 3–5 kDa peptide in a <10 kDa peptide fraction; this peptide fraction was also released with a daily rhythm but possessed weak steroidogenic activity. The natural PTTH of Rhodnius, therefore, appears to be a 68 kDa peptide, possibly composed of several 17 kDa subunits, that is related to Bombyx PTTH.