EFFECTS OF PRELOAD AND AFTERLOAD ON THE PERFORMANCE OF THE IN-SITU PERFUSED PORTAL HEART OF THE NEW-ZEALAND HAGFISH EPTATRETUS-CIRRHATUS

The portal heart of the New Zealand hagfish (Eptatretus cirrhatus) was perfused in situ. Stroke volume, cardiac output and power output incr eased in response to increased preload, in accordance with Starling's law of the heart, A positive chronotropic effect was found when the in put pressure increased from 0.05 to 0.1 kPa. Increased afterload decre ased stroke volume and cardiac output, Power output peaked at an outpu t pressure of 0.22 kPa, after which it decreased, There was no change in heart rate in response to increased afterload, In unanaesthetized r esting animals, the pressure in the supraintestinal vein, which suppli es the portal heart, ranged from 0.025 to 0.07 kPa (mean 0.040+/-0.005 kPa). The beta-adrenoceptor antagonist sotalol did not affect the res ponse to different input and output pressures, Sotalol produced a sign ificant decrease in heart rate and abolished the pressure-sensitive in crease in heart rate, Bolus injections of adrenaline produced a transi ent increase in portal heart rate, The negative chronotropic response to sotalol and the response to adrenaline indicate the presence of an endogenous beta-adrenergic tonus on the portal heart.