QUANTIFICATION OF MANDUCA ADIPOKINETIC HORMONE IN NERVOUS AND ENDOCRINE TISSUE BY A SPECIFIC RADIOIMMUNOASSAY

A specific radioimmunoassay (RIA) procedure was used to estimate the amount of the nonapeptide hormone Manduca adipokinetic hormone contained in endocrine and nervous tissues of the tobacco hornworm, Manduca sexta. In both adults and larvae almost all (>90%) of the Manduca adipokinetic hormone immunoreactivity was present in the corpora cardiaca. A small amount of immunoreactive material was present in adult brain, but adult nerve cord and larval brain and nerve cord contained only background levels of activity. The identity of immunoreactive material was investigated by combining RIA with reverse-phase high performance liquid chromatography (RP-HPLC). The material in the corpora cardiaca was found to coelute with synthetic Manduca adipokinetic hormone on RP-HPLC. The small amount of immunoreactive material in adult brain did not coelute with synthetic peptide and is not though to represent authentic Manduca adipokinetic hormone. The data from the quantification experiments were used to compare the bioactivity of larval and adult corpora cardiaca extracts with synthetic Manduca adipokinetic hormone. Such comparisons support the identification of this peptide as the larval glycogen phosphorylase activating hormone, but suggest that it may not be the only factor involved in the regulation of haemolymph lipid levels in adult moths. © 1990.