The effects of six pericardial hormones and hypoxia on the semi-isolated heart and sternal arterial valve of the lobster Homarus americanus

Abstract

Each of three amine and three peptide hormones of the pericardial organs exerts a unique effect on heart rate and ventricular pressure, and on outflow through the sternal arterial valve in Homarus americanus. At the concentrations of 0.1-0.25 μM, all of the six hormones except crustacean cardioactive peptide (CCAP) increased heart rate while only two (proctolin and F2) significantly increased ventricular pressure. Octopamine by itself had almost no effect, but augmented ventricular pressure when combined with proctolin. Whenever a hormone caused an increase in ventricular pressure, there was also an increase in dorsal abdominal artery pressure or flow. All hormones except dopamine caused a reduction in sternal artery flow. Dopamine by relaxing the sternal arterial valve increased the sternal flow, but it had no effect on ventricular pressure or dorsal abdominal artery flow. CCAP and serotonin did not significantly change the magnitudes of ventricular pressure or dorsal abdominal flow, but both reduced flow in the sternal artery. Hypoxia depressed heart rate and to a lesser extent contractility, but did not alter the responsiveness of the heart or sternal arterial valve to hormones.