Modulation of cardiac rhythm by allatostatins in the cockroach Blattella germanica (L.) (Dictyoptera, Blattellidae)

Cardiac rhythm was measured in Blattella germanica females during the repro ductive cycle. The rate increased from day 0 to 1, remained constant during the vitellogenic period and fell by about 20% during the period of ootheca l transport. The effects of allatostatins, allatostatin analogues and coraz onin were tested on semi-isolated heart preparations. Allatostatins showed a rapid, reversible and dose-dependent cardioinhibitory activity. Blattella allatostatin 1 (BLAST-1: LYDFGL-NH2), was the most active, eliciting 76% i nhibition at 10(-7) M and even 19% inhibition at 10(-9) M. BLAST-2 (DRLYSFG L-NH2), BLAST-3 (AGSDGRLYSFGL-NH2) and BLAST-4 (APSSAQRLYGFGL-NH2) were les s active. An analogue of BLAST-2 with C-terminus in acid form and a pseudop eptide analogue of BLAST-2 with a methyleneamino Psi[CH2NH] peptide bond su rrogate between residues L-3 and Y-4 were inactive. Corazonin elicited rapi d, reversible and dose-dependent cardioacceleratory activity. When tested t ogether with BLAST-1, corazonin overrode the cardioinhibitory effect of all atostatin. Our previous results had shown that high levels of allatostatin were maintained during die period of oothecal transport. This and the fact that physiological concentrations of allatostatins produce physiological le vels of inhibition, suggest that allatostatins are involved in the modulati on of cardiac rhythm in this cockroach. (C) 1999 Elsevier Science Ltd. All rights reserved.