The effect of corazonin on heartbeat reversal in pupae of the tobacco hornworm, Manduca sexta (Lepidoptera: Sphingidae)

Abstract

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 [Arg 7 ]-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 -7 M 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.

Effect of corazonin and crustacean cardioactive peptide on heartbeat in the adult American cockroach (Periplaneta americana)

“…We have recently investigated the possible effects of corazonin on the heartbeat in pupae of the tobacco hornworm (Manduca sexta: Lepidoptera) and yellow mealworm (Tenebrio molitor: Coleoptera) (Sláma, 2004). There was no effect on the rate of the heartbeat, except for a brief tachycardia immediately after the injections in Manduca.…”

“…Since all previous reports on cardiostimulating activity of corazonin were reached by the assays in vitro (Veenstra, , 1990, we can conclude that solid evidence for the in vivo effects of corazonin on the dorsal vessel of insects actually does not exist. Recent studies in Manduca (Sláma and Miller, 2001;Sláma, 2004;Sláma and Rosi½ski, 2004) and Drosophila (Sláma and Farkaš, 2005) suggest an immediate, feedback regulation of cardiac functions by the low molecular metabolites, without direct dependence on the synthesis of neuropeptides.…”

“…After extensive discussions on this point (see Sláma, 2004, for references), it was determined that the process of enzymatic hydrolysis in vivo does not play a significant role in the biological activity of the peptides. Proctolin, for example, injected in concentrations several orders of magnitude below the K m constants of the degrading enzymes (10 -9 M in the body), caused prolonged pharmacological effects on abdominal intersegmental muscles regulating hemocoelic pressure in pupae of Tenebrio (Sláma et al, 1993).…”

“…We have described the effects of corazonin and crustacean cardioactive peptide (CCAP) on heartbeat in pupae of the tobacco hornworm, Manduca sexta (Sláma, 2004) In this model system, corazonin had no effect on the heartbeat, except for a brief tachycardia induced by the relatively large dosages (equivalent to 10 -6 M concentrations of corazonin in the body). In the present work, we have extended these studies with the application of touch-free, noninvasive optoelectronic methods (Sláma, 2003(Sláma, , 2004 for recording the effects of corazonin and CCAP on the heartbeat of the American cockroach.…”

“…In the present work, we have extended these studies with the application of touch-free, noninvasive optoelectronic methods (Sláma, 2003(Sláma, , 2004 for recording the effects of corazonin and CCAP on the heartbeat of the American cockroach. The acute problem of immobilization was solved by using the motionless decapitated adults (Anderson et al, 1990), which survived well for several days or weeks due to the regulatory functions of the autonomic nervous system (coelopulse; Sláma, 1999Sláma, , 2000.…”