ACE and ANG II independently modulate steroidogenesis and prostaglandin production in amphibian gonads “in vitro”.

The aim of the present research was to study the role of angiotensin converting enzyme (ACE) and angiotensin II (ANG II) in amphibian (Rana esculenta) steroidogenesis and prostaglandin production. Hormonal effects of ACE, ACE inhibitors, synthetic bullfrog ANG I and [Val5]ANG II were determined in ovary and testis in the prereproductive period. Production of 17β-estradiol, progesterone, androgens, and prostaglandin F2α (PGF2α) and prostaglandin E2 (PGE2)was determined incubating frog ovary and testis with ACE (2.5 mU/ml), captopril (1 mM), lisinopril (0.1 mM), [Val5]ANG II (1 µM), and synthetic bullfrog ANG I (1 µM). The data analysis showed an independent modulation of steroids and prostaglandin production by ACE and ANG II. In the ovary, ACE modulated 17β-estradiol, progesterone and PGE2 production; on the other hand, [Val5]ANG II modulated the production of progesterone and PGF2α, whereas androgens production was not affected. In the testis, ACE caused a decrease of 17β-estradiol production and an increase of androgens production, while [Val5]ANG II showed an opposite effect, decreasing androgen production and increasing 17β-estradiol. The determination of testicular aromatase activity showed a positive regulation by [Val5]ANG II and negative one by ACE. The data obtained suggest the presence of two pathway, independently regulated by ACE and [Val5]ANG II, modulating ovarian and testicular steroidogenesis and prostaglandin production. In an attempt to identify the peptide involved in the pathway modulated by ACE, the bradykinin, another physiological substrate of ACE, was chosen. To prove that ACE of frog hydrolyzes bradykinin, purified ovary membranes were incubated at 37°C in presence of peptide, and the hydrolytic products were analyzed by reverse-phase HPLC. The results show that bradykinin was metabolized by neutral endopeptidase (NEP) and ACE. Frog ovary was incubated “in vitro” in presence of bradykinin (10 µM), ACE (2.5 mU/ml), captopril (0.1 mM), lisinopril (0.1 mM), NPC567 (1 µg/ml), and 1-7 bradykinin (10 µM). The results showed no modulating activity by bradykinin on ovarian 17β-estradiol and PGE2 production, while the data obtained, demonstrate that bradykinin was not involved in the ACE-modulated pathway.