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Angiotensin converting enzyme (ACE) is the dipeptidyl-carboxypeptidase of the renin-angiotensin system involved in the control of blood pressure and hydromineral metabolism. It converts angiotensin I to angiotensin II, the biologically active octapeptide. Angiotensin converting enzyme-like activity has been demonstrated in a wide range of vertebrates. The presence of ACE was investigated in tissues of two amphibian species, the frog Rana esculenta and the toad Xenopus laevis. ACE activities were determined by specific substrate hydrolysis in gut, gonads, lung, kidney, heart, liver, skin, erythrocytes, and muscle homogenates and plasma by means of high performance liquid chromatography. Significant ACE activity was found in gut, gonads, lung and kidney, while that in heart, liver, skin, erythrocytes, muscle, and plasma was very low. Testis of toad contained the highest ACE activity, while that in erythrocytes of male and female frogs was notable.

Gonad, lung, kidney and serum angiotensin converting enzyme (ACE) activities were determined by specific substrate hydrolysis in male and female Rana esculenta over 1 year. Ovary ACE activity showed the highest values among the different tissues, with a significant peak (223+/-52 nmol min(-1) mg protein(-1)) in late winter-early spring. Testis ACE activity followed a significant seasonal cycle, increasing from September to peak in April (2.5+/-0.8 nmol min(-1) mg protein(-1)) and then decreased in the post-reproductive period. Lung and kidney ACE activities were not correlated with the annual reproductive cycle phases. In serum a peak of activity was present in the post-reproductive period both in male and female frogs. The present data show a correlation between ACE and the annual reproductive cycle of R. esculenta.