COMPARISON OF TEMPERATURE EFFECTS ON HEART PERFORMANCE OF THE DUNGENESS CRAB, CANCER-MAGISTER, IN-VITRO AND IN-VIVO

A large percentage of physiological studies are based on isolated comp onents of complex systems, but the question can always be posed, are t he responses the same in isolation as when these components are under the homeostatic controls that exist in vivo? For cardiac performance i n Cancer magister, the responses to temperature variation over the ran ge 4 degrees to 20 degrees C are different in semi-isolated hearts tha n in intact animals. Cardiac performance in semi-isolated hearts was m easured with a pressure transducer, a flow transducer, and electromyog ram (EMG) electrodes, and in intact animals with pulsed Doppler flow p robes. Heart rate increase in semi-isolated hearts was about one-third of that in intact animals. The cardiac output of semi-isolated hearts decreased with increasing temperature, whereas that of intact animals increased. Stroke volume decreased linearly in semi-isolated hearts. In intact animals, stroke volume decreased from 4 degrees to 12 degree s C, but remained relatively stable from 12 degrees to 20 degrees C Th e ventricular pressure and the EMG amplitude of semi-isolated hearts b oth decreased with increasing temperature. Double systolic contraction s appeared both in semi-isolated hearts and in intact animals in the t emperature range 13 degrees to 20 degrees C; this may represent a comp ensatory mechanism at extreme temperatures. The difference in cardiac performance between intact crabs and semi-isolated hearts reflects, al most certainly, extrinsic control in intact animals, including modulat ion by cardioregulatory nerves or neurohormonal modulation of the card iac ganglion, myocardial contractility or changes in outflow resistanc e.