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Our aim was to study the role of angiotensin-converting enzyme (ACE) and angiotensin II (ANG II) on ovarian steroidogenesis and prostaglandin production of amphibian. Hormonal effects of ACE, ACE inhibitors, synthetic bullfrog angiotensin I (ANG I), and [Val5]ANG II were compared on frog ovaries of postreproductive and prereproductive periods. Very high ACE activity was found in ovary of water frog ( Rana esculenta) compared with other frog tissues, and this activity was inhibited by the typical ACE inhibitors, captopril and lisinopril. Frog ovary tissue in postreproductive and prereproductive periods was incubated in vitro in the presence of ACE (2.5 mU/ml), captopril (0.1 mM), lisinopril (0.1 mM), [Val5]ANG II (1 μM), and synthetic bullfrog ANG I (1 μM). Production of 17β-estradiol, progesterone, androgens, and prostaglandins E2 and F2α was determined. The data showed a modulation of 17β-estradiol, progesterone, and prostaglandin E2 production by ovary ACE; on the other hand, [Val5]ANG II modulated the production of progesterone and prostaglandin F2α, whereas androgen production was not influenced. The present in vitro studies suggest the existence of two pathways independently regulated by ACE and ANG II modulating ovarian steroidogenesis and prostaglandin production.

The Authors describe the purification of swine serum ACE to molecular homogeneity with high recovery of activity (40 %) in a few stepsl The purification procedure consists of affinity chromatography, using commercial activated resin (epoxy-activated sepharose 6B) and two steps of anion exchange chromatography (Resource Q) performed at different pH (pH 9.0 and pH 6.0). Furthermore, a specific and sensitive method for the accurate quantitation of ACE activity in biological fluids was developed, based on the hydrolysis of synthetic FAPGG (N-[3-(2-furyl) acryloyl] L-phenylalanyl glycyl glycine), as substrate and following the separation of products by reversed-phase HPLC. Some kinetic parameters were determined. The Km and Kcat values for FAPGG were 0.793 + 0.052 mM and 5830 s -1, respectively, and the I50 values for captopril and lisinopril, two specific ACE inhibitors, are 5.7 • 0.67 nM and 1.0 • 0.29 nM, respectively.

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