THE RENIN-ANGIOTENSIN SYSTEM IN BLOOD PRESSURE CONTROL DURING EXERCISE IN THE COD GADUS MORHUA

The effects of angiotensin I, angiotensin II and exercise on ventral and dorsal aortic blood pressure and heart rate were investigated in the Atlantic cod, Gadus morhua. Both angiotensins produced a marked increase in blood pressure. After injection of the angiotensin-converting enzyme (ACE) inhibitor enalapril, both ventral and dorsal blood pressures decreased significantly and the effect of angiotensin I was abolished. This demonstrates that ACE activity is necessay for conversion of angiotensin I to angiotensin II in the cod, as in other teleosts investigated, and provides a tool for further study of angiotensin function. During swimming exercise at 2/3 body lengths per second, ventral and dorsal aortic blood pressures increased, but this exercise hypertension was absent in fish pretreated with the alpha-adrenoceptor antagonist prazosin. Instead, an increase in both ventral and dorsal aortic blood pressures occurred immediately after the exercise period. This post-exercise hypertension could be abolished by injection of enalapril, suggesting that the angiotensin system is the responsible ‘anti-drop’ factor activated in the absence of a functional adrenergic vasomotor control. We conclude that the angiotensin system provides a major contribution to the resting blood pressure regulation in the cod, and that this system can be activated to offset a decrease in arterial blood pressure.