Materials and Methods: A strip of rabbit corpus cavernosum was mounted in an organ chamber to measure the isometric tension. The specific binding for I-125-ANG II was characterized by in vitro autoradiography.

Results: ANG II and ANG I, precursor of ANG II, contracted corpus cavernosum smooth muscle dose-dependently, but the response of smooth muscle to ANG I was 10-fold less than that to ANG II, Contractile responses of smooth muscle to ANG II and ANG I were blocked by Dup 753, a specific inhibitor of ANG II type 1 receptor, but not by PD 123,319, a specific inhibitor of ANG II type 2 receptor. The effect of ANG I was attenuated by captopril, an inhibitor of ACE. Specific binding sites for I-125-ANG II were found in the corpus cavernosum. The dissociation constant (K-d) was 5.32 +/- 1.65 nM, and maximum binding capacity (B-max) was 305.72 +/- 85.24 amol/mm.(2) Specific binding of I-125-ANG II was displaced by Dup 753 (10(-6) M) but not by PD 123,319 (10(-5) M). The inhibitory constant (K-i) for Dup 753 was 8.09 +/- 2.51 nM.

Conclusion: The present results suggest that the renin-angiotensin system is involved in the regulation of corpus cavernosum smooth muscle tone bf rabbit and the ANG II receptor subtype AT1 is important in the regulation of penile erection.