Factors affecting arterial pressures and blood flow from the heart in intact, unrestrained lingcod, Ophiodon elongatus

1. 1. Increases in temperature resulted in large increases in heart rate but caused little change in stroke volume. Injections of atropine into the pericardial cavity caused an increase in heart rate, a decrease in stroke volume but little change in cardiac output. 2. 2. Injections of adrenaline into the dorsal aorta resulted in a rise in dorsal aortic blood pressure and a fall in heart rate and cardiac output. In the atropinized fish, adrenaline injections into the dorsal aorta caused a rise in dorsal aortic blood pressure, a fall in cardiac output but no change in heart rate. Blockade of α-adrenergic receptors with phenoxybenzamine abolished the circulatory changes associated with adrenaline injections. Addition of adrenaline to the water in which the fish was situated resulted in an increase in cardiac output and stroke volume, with little change in heart rate. 3. 3. Cardiovascular changes associated with swimming were similar to those that occurred when the animal was disturbed. There was a bradycardia, with little change in stroke volume. In the atropinized fish, exercise was associated with an increase in cardiac output and stroke volume with little change in heart rate.