A microdialysis study of allatostatin degradation in Blattella germanica (L.) (Dictyoptera, Blattellidae)

Allatostatins with a typical C-terminal sequence YXFGL-NH2 are insect neuropeptides with inhibitory properties upon Juvenile Hormone production in the corpora allata, vitellogenin release by the fat body, and gut and dorsal vessel motility. All these biological effects are rapidly reversible, suggesting the occurrence of effective mechanisms for inactivation of the peptides. We have studied the degradation of DRLYSFGL-NH2 (BLAST-2), one of the allatostatins of Blattella germanica, in the internal milieu of adult females of this cockroach, The experimental approach combined the use of the radioiodinated derivative [I-125-Tyr(4)]BLAST-2, microdialysis techniques and HPLC analysis with a radioisotope detector. Under these experimental conditions, the half-life of BLAST-2 in the internal milieu of the adult female of B. germanica was between 3 and 6 min. Such a short half-life explains the high doses of allatostatins required to obtain the expected biological effects when tested in vivo, and suggests that circulating allatostatins are subject to rapid rates of synthesis and degradation in order to be operative physiologically.