Abstract
Heartbeat reversal patterns have been monitored in the body of diapausing pupae of M. sexta 2 h before and 3 h after the injections of [Arg7]-corazonin, using noninvasive thermographic and optocardiographic methods. Large dosages (10-6 M final concentrations of corazonin in the body) caused almost immediate, adrenaline-like enhancement of the anterograde heartbeat. During the relatively short, acute phase of the tachycardia induced by corazonin, the systolic anterograde contractions of the heart increased in average from 10.5 to 24 pulses per min, culminating at 2.5 min after the injections. Duration of the acute period of tachycardia was only 7 to 20 min, which was followed by a period of slightly elevated, residual anterograde heartbeat which persisted occasionally for 1 to 3 h. Smaller dosages of corazonin (10-7M concentrations in the body) occasionally also produced a less intensive cardiotropic effect, while the more diluted samples were completely inactive. In pupae of the beetle T. molitor, injections of corazonin (10-6 M in the body) had no effect on the rate of in vivo heartbeat at all. Pharmacological analysis of the effects of corazonin in M. sexta indicated that the cardiostimulating effects of corazonin did not conform with the expected action of a peptidic neurohormone. A possibility that these effects might be artifacts produced by the low molecular breakdown products of corazonin has been discussed.
Highlights
In the literature, corazonin is commonly introduced by a statement: “[Arg(7)]-corazonin was first isolated from P. americana as a potent cardioaccelerator (Veenstra, 1989)” (Qi-Miao et al, 2003)
Cardiostimulating effects of very short duration, which we have obtained with corazonin in diapausing pupae of M. sexta, show apparent similarities with the results obtained from other neuropeptides in the puparia of Drosophila (Nichols et al, 1999; Zornik et al, 1999)
Similar effects have been previously reported in numerous in vitro cardiological investigations including: a) corazonin (Veenstra, 1990, 1991); b) Proctolin and a number of its derivatives (KonopiĔska et al, 1992; RosiĔski, 1995); c) neuropeptides of other families (Holman et al, 1990; Nässel et al, 2002), and; c) numerous low molecular neuroactive compounds (Jones, 1977; Miller, 1979, 1997)
Summary
Corazonin is commonly introduced by a statement: “[Arg(7)]-corazonin was first isolated from P. americana as a potent cardioaccelerator (Veenstra, 1989)” (Qi-Miao et al, 2003). The cardioaccelerating properties of corazonin have been widely advertised, experimental evidence for cardiostimulating action of corazonin is limited to just a few in vitro observations on the explanted dorsal vessels (Veenstra, 1989; Predel et al, 1994; Vilaplana et al, 1999). In addition to corazonin cardiostimulating properties were ascribed to several other groups of insect peptides (review by Holman et al, 1990; KonopiĔska et al, 1992; RosiĔski, 1995; Nässel et al, 2002). According to Schoofs et al (2001), structural information was available in 2001 for more than 60 peptides only in locusts. Biological activity of these peptides was usually estimated by in vitro assays, based on the increased contractions of the visceral muscles. The in vivo effects of corazonin were further extended to acceleration of egg development and inhibition of food intake in locusts (Schoofs et al, 2001), reduced rate of spinning in silkworm larvae (Tanaka et al, 2002), or influence on the phase transition in locusts (Hoste et al, 2002; Breuer et al, 2003; Rahman et al, 2003)
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