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.

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