PEPTIDERGIC MODULATION OF CARDIAC-PERFORMANCE IN ISOLATED HEARTS FROMTHE SHORE CRAB CARCINUS-MAENAS

The present study examined the effects of two peptide hormones on rate , pressures, and flow generated by isolated in situ crustacean hearts. Saline, pumped by spontaneous contractions, was collected through a c annula attached to the sternal artery. Cardiac flow was measured direc tly with an electromagnetic flow probe, while arterial and ventricular pressures were recorded with pressure transducers. Crustacean cardioa ctive peptide (CCAP), known to be present in the pericardial organs of Carcinus, increased cardiac output mainly by increasing heart rate. O n average, CCAP caused a modest increase in stroke volume. Proctolin, another peptide found in the pericardial organs, also increased cardia c output, but generally elicited large changes in the stroke volume. P roctolin also increased heart rate, but to a lesser extent than did CC AP. Both peptides increased ventricular pressure, stroke work, and car diac power. Mean effective dose (ED50 values associated with the effec ts on heart rate were approximately 4 X 10(-9) for proctolin and 1 X 1 0(-7) mol . L-1 for CCAP. Responses to the peptides did not indicate r eceptor desensitization. The results support the hypothesis that hormo nes from the pericardial organs play a physiological role in modulatin g cardiac output in crustaceans.